http://www.mdpi.com/journal/crystals Latest open access articles published in Crystals at http://www.mdpi.com/journal/crystals http://www.mdpi.com/2073-4352/3/2/363 Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature of domain structure, microscopic smectic phase structure, relaxation mechanism, and sample history. These aspects of liquid crystal elastomers are briefly reviewed followed by a summary of the results of recent elastic and high-resolution X-ray diffraction studies of the shape memory effect and the dynamics of the formation of the smectic-C chevron-like layer structure. A possible route to realizing auxetic effect at molecular level is also discussed. Crystals 2013-06-07 3 2 Review 10.3390/cryst3020363 363 390 2073-4352 2013-06-07 doi: 10.3390/cryst3020363 Sonal Dey Dena Agra-Kooijman Wanting Ren Philip McMullan Anselm Griffin Satyendra Kumar http://www.mdpi.com/2073-4352/3/2/350 The new phosphine oxide compound, (dimethylphosphoryl)methanaminium perchlorate, dpmaHClO4 (1), was synthesized by the reaction of (dimethylphosphoryl) methanamine (dpma) with concentrated perchloric acid. (Dimethylphosphoryl)methanaminium perchlorate (dimethylphosphoryl)methanamine solvate, dpmaHClO4•dpma (2) was obtained by the slow evaporation of an equimolar methanolic solution of 1 and dpma at room temperature. For both compounds, single-crystal X-ray structures, IR and Raman spectra are reported. The assignment of the spectroscopic data were supported by quantum chemical calculations at the B3LYP/6-311G(2d,p) level of theory. In 1, the dpmaH cations form polymeric, polar double-strands along [010] by head to tail connections via N–H∙∙∙O hydrogen bonds. The perchlorate anions are located between these strands attached by one medium strong and two weaker un-bifurcated hydrogen bonds (monoclinic, centrosymmetric space group C2/c, a = 17.8796(5) Å, b = 5.66867(14) Å, c = 17.0106(5) Å, β = 104.788(3)°, V = 1666.9(1) Å3, Z = 8, T = 293 K, R(F) [I > 2σ(I)] = 0.0391, wR(F2) [all] = 0.1113). In 2, besides the N–H∙∙∙O hydrogen bonds, medium strong N–H∙∙∙N hydrogen bonds are present. One dpmaH cation and the neutral dpma molecule are connected head to tail by two N–H∙∙∙O hydrogen bonds forming a monocationic cyclic unit. These cyclic units are further connected by N–H∙∙∙O and N–H∙∙∙N hydrogen bonds forming polymeric, polar double-strands along [001]. The perchlorate anions fill the gaps between these strands, and each [ClO4]− anion is weakly connected to the NH2 group by one N–H∙∙∙O hydrogen bond (orthorhombic, non-centrosymmetric space group Pca21 (No. 29), a = 18.5821(5) Å, b = 11.4320(3) Å, c = 6.89400(17) Å, V = 1464.50(6) Å3, Z = 4, T = 100 K, R(F) [I > 2σ(I)] = 0.0234, wR(F2) [all] = 0.0575). Both structures are structurally related, and their commonalities are discussed in terms of a graph-set analysis. Crystals 2013-06-05 3 2 Article 10.3390/cryst3020350 350 362 2073-4352 2013-06-05 doi: 10.3390/cryst3020350 Daniel Buhl Hülya Gün Alexander Jablonka Guido Reiss http://www.mdpi.com/2073-4352/3/2/339 Fluoro substitution in thermotropic liquid crystals provides a general way of modifying the properties of a parent system. Transition temperatures, mesophase types and other physical properties can be affected by fluoro substitution, so that frequently the behaviors of the parent compound can be manipulated and improved in a predictable manner. This paper discusses the effects of a fluoro substitution in each side-arm of 1,2,4,5-tetrakis((4-(alkoxy)phenyl)ethynyl)benzenes on the resulting mesomorphic properties characterized by optical polarizing microscopy and differential scanning calorimetry. Without any fluoro-substituted side-arms, longer chain-length leads to a wider nematic temperature range on cooling. Incorporation of a fluoro substitution in each side-arm induces the formation of a lamellar suprastructure, lowers transition temperatures and results in a wider mesophase temperature range on cooling. Crystals 2013-05-30 3 2 Article 10.3390/cryst3020339 339 349 2073-4352 2013-05-30 doi: 10.3390/cryst3020339 Yi-Hui Lin Yamuna Ezhumalai Yu-Ling Yang Ching-Ting Liao Hsiu-Fu Hsu Chunhung Wu http://www.mdpi.com/2073-4352/3/2/333 A 3-hydro-4-pyridinone compound derived from maltol and dopamine has been prepared using a microwave reactor. The molecular structure of the protonated product was confirmed by single crystal X-ray diffraction. Crystals were obtained from a saturated solution of methanol and belong to the triclinic space group P-1 with unit cell parameters a = 8.3801(11) Å; b = 9.2583(12) Å; c = 11.5671(15) Å; α = 73.566(2)°; β = 84.514(2)°; γ = 66.578(2)°. The asymmetric unit contains two molecules. Crystals 2013-05-17 3 2 Short Note 10.3390/cryst3020333 333 338 2073-4352 2013-05-17 doi: 10.3390/cryst3020333 Steven Hall Raymond Roy Dylan McLaughlin Kate Sullivan L. Barclay Christopher Vogels Andreas Decken Stephen Westcott http://www.mdpi.com/2073-4352/3/2/315 Hopping dynamics in glass has been known for quite a long time. In contrast, hopping dynamics in smectic-A (SmA) and hexatic smectic-B (HexB) liquid crystals (LC) has been observed only recently. The hopping in SmA phase occurs among the smectic layers (one-dimensionally), while hopping in HexB phase occurs inside the layers (two-dimensionally). The hopping dynamics in SmA and HexB liquid crystal phases is investigated by parallel soft-core spherocylinders, while three-dimensional hopping dynamics in inherent glassy states is investigated by systems of Weeks–Chandler–Andersen (WCA) spheres. The temperature dependence of diffusion coefficients of hopping in SmA phase can be described by the Arrhenius equation characteristic of activation process. In HexB LC phase, the diffusion coefficients saturate at higher temperatures. In a system of WCA spheres, the values and temperature dependence of diffusion coefficients depend on the observed states. Crystals 2013-04-29 3 2 Review 10.3390/cryst3020315 315 332 2073-4352 2013-04-29 doi: 10.3390/cryst3020315 Keiko Aoki Susumu Fujiwara Kiyoshi Sogo Shuhei Ohnishi Takenori Yamamoto http://www.mdpi.com/2073-4352/3/2/306 The glycine betaine (betaine), interacts with several types of proteins with diverse structures in vivo, and in the contact regions, the aromatic rings of protein residues are frequently found beside the trimethylammonium group of betaine, implying the importance of the cation−π interactions in recognition of this molecule. The crystal structures determined by X-ray crystallography of the complexes of betaine and C-ethyl-pyrogallol[4]arene (pyrogallol cyclic tetramer: PCT) and betaine and C-ethyl-resorcin[4]arene (resorcinol cyclic tetramer: RCT) mimic the conformations of betaine and protein complexes and show that the clathrate conformations are retained by the cation−π interactions. The difference of the conformation feature of betaine in the Protein Data Bank and in the Cambridge Structural Database was found by chance during the research and analyzed with the torsion angles. Crystals 2013-04-16 3 2 Article 10.3390/cryst3020306 306 314 2073-4352 2013-04-16 doi: 10.3390/cryst3020306 Ikuhide Fujisawa Katsuyuki Aoki http://www.mdpi.com/2073-4352/3/2/289 We present a survey of the effect of vacancies on quantum transport in graphene, exploring conduction regimes ranging from tunnelling to intrinsic transport phenomena. Vacancies, with density up to 2%, are distributed at random either in a balanced manner between the two sublattices or in a totally unbalanced configuration where only atoms sitting on a given sublattice are randomly removed. Quantum transmission shows a variety of different behaviours, which depend on the specific system geometry and disorder distribution. The investigation of the scaling laws of the most significant quantities allows a deep physical insight and the accurate prediction of their trend over a large energy region around the Dirac point. Crystals 2013-04-08 3 2 Article 10.3390/cryst3020289 289 305 2073-4352 2013-04-08 doi: 10.3390/cryst3020289 Alessandro Cresti Thibaud Louvet Frank Ortmann Dinh Van Tuan Paweł Lenarczyk Georg Huhs Stephan Roche http://www.mdpi.com/2073-4352/3/2/275 Reactions of a mononuclear molybdenum(V) starting material, (PyH)5[MoOCl4(H2O)]3Cl2, with 2,2-dimethylsuccinic acid in the presence of base afforded two products, (PyH)3[Mo2O4Cl4(μ2-dmsH)]·1/2CH3CN (1) and (PyH)4[Mo2O4Cl4(μ2-dmsH)]Cl (2). As revealed by the X-ray structure analysis, the half-neutralized form of the dicarboxylic acid, the dmsH− ion, coordinated to the well-known {Mo2O4}2+ core in the syn-syn bidentate bridging manner. In both compounds, the non-ionized terminus of the ligand, the COOH function, participated in hydrogen-bonding interactions. The incorporation of the chloride counteranion in 2, prevented the formation of the common “carboxylic acid dimer” which was observed for 1. Instead, a hydrogen-bonded linkage of the COOH function with the chloride occurred. Crystals 2013-04-03 3 2 Article 10.3390/cryst3020275 275 288 2073-4352 2013-04-03 doi: 10.3390/cryst3020275 Barbara Modec http://www.mdpi.com/2073-4352/3/1/257 The contact resistance between graphene and metal electrodes is crucial for the achievement of high-performance graphene devices. In this study, we review our recent study on the graphene–metal contact characteristics from the following viewpoints: (1) metal preparation method; (2) asymmetric conductance; (3) annealing effect; (4) interfaces impact. Crystals 2013-03-18 3 1 Review 10.3390/cryst3010257 257 274 2073-4352 2013-03-18 doi: 10.3390/cryst3010257 Wenjun Liu Jun Wei Xiaowei Sun Hongyu Yu http://www.mdpi.com/2073-4352/3/1/248 4-(Dimethylamino)benzaldehyde is alkylated at the N atom by dialkyl sulfates, MeI, or Me3O BF4. In contrast, ethylation by Et3O BF4 occurs selectively at the O atom yielding a quinoid iminium ion. 4-(Diethylamino)benzaldehyde is alkylated only at O by either Et or Me oxonium reagent. The iminium salts are prone to hydrolysis giving the corresponding hydrotetrafluoroborates. Five crystal structures were determined. Crystals 2013-03-18 3 1 Article 10.3390/cryst3010248 248 256 2073-4352 2013-03-18 doi: 10.3390/cryst3010248 Carmen Froschauer Hedda Weber Volker Kahlenberg Gerhard Laus Herwig Schottenberger http://www.mdpi.com/2073-4352/3/1/234 Circularly polarized light was previously employed to stimulate the reversible and reconfigurable writing of scattering states in cholesteric liquid crystal (CLC) cells constructed with a photosensitive layer. Such dynamic photodriven responses have utility in remotely triggering changes in optical constructs responsive to optical stimulus and applications where complex spatial patterning is required. Writing of scattering regions required the handedness of incoming radiation to match the handedness of the CLC and the reflection bandwidth of the CLC to envelop the wavelength of the incoming radiation. In this paper, the mechanism of transforming the CLC into a light scattering state via the influence of light on the photosensitive alignment layer is detailed. Specifically, the effects of: (i) the polarization state of light on the photosensitive alignment layer; (ii) the exposure time; and (iii) the incidence angle of radiation on domain formation are reported. The photogenerated light-scattering domains are shown to be similar in appearance between crossed polarizers to a defect structure that occurs at a CLC/air interface (i.e., a free CLC surface). This observation provides strong indication that exposure of the photosensitive alignment layer to the circularly polarized light of appropriate wavelength and handedness generates an out-of-plane orientation leading to a periodic distortion of the original planar structure. Crystals 2013-03-18 3 1 Article 10.3390/cryst3010234 234 247 2073-4352 2013-03-18 doi: 10.3390/cryst3010234 Jonathan Vernon Svetlana Serak Rafael Hakobyan Vincent Tondiglia Timothy White Nelson Tabiryan Timothy Bunning http://www.mdpi.com/2073-4352/3/1/191 We present local electrical characterization of epitaxial graphene grown on both Si- and C-faces of 4H-SiC using Electrostatic Force Microscopy and Kelvin Probe Force Microscopy in ambient conditions and at elevated temperatures. These techniques provide a straightforward identification of graphene domains with various thicknesses on the substrate where topographical determination is hindered by adsorbates and SiC terraces. We also use Electrostatic Force Spectroscopy which allows quantitative surface potential measurements with high spatial resolution. Using these techniques, we study evolution of a layer of atmospheric water as a function of temperature, which is accompanied by a significant change of the absolute surface potential difference. We show that the nanoscale wettability of the material is strongly dependent on the number of graphene layers, where hydrophobicity increases with graphene thickness. We also use micron-sized graphene Hall bars with gold electrodes to calibrate work function of the electrically conductive probe and precisely and quantitatively define the work functions for single- and double-layer graphene. Crystals 2013-03-13 3 1 Review 10.3390/cryst3010191 191 233 2073-4352 2013-03-13 doi: 10.3390/cryst3010191 Olga Kazakova Vishal Panchal Tim Burnett http://www.mdpi.com/2073-4352/3/1/163 Graphene is a promising electrode material for supercapacitors mainly because of its large specific surface area and high conductivity. In practice, however, several fabrication issues need refinement. The restacking of graphene flakes upon being packed into supercapacitor electrodes has become a critical challenge in the full utilization of graphene’s large specific surface area to further improve the device performance. In this review, a variety of recent techniques and strategies are overviewed for the prevention of graphene restacking. They have been classified into several categories to improve and facilitate the discussion on the underlying ideas. Based on the overview of the existing techniques, we discuss the trends of future research in the fields. Crystals 2013-03-06 3 1 Review 10.3390/cryst3010163 163 190 2073-4352 2013-03-06 doi: 10.3390/cryst3010163 Jiantong Li Mikael Östling http://www.mdpi.com/2073-4352/3/1/149 Photoalignment possesses obvious advantages in comparison with the usually “rubbing” treatment of the substrates of liquid crystal display (LCD) cells. The application of the photoalignment and photopatterning nanotechnology for the new generation of photonic and display devices will be reviewed. Crystals 2013-03-01 3 1 Review 10.3390/cryst3010149 149 162 2073-4352 2013-03-01 doi: 10.3390/cryst3010149 Vladimir Chigrinov http://www.mdpi.com/2073-4352/3/1/141 Ferrocenoindenes display planar chirality and thus represent valuable ligands for asymmetric catalysis. Here, we report on the synthesis of novel 3-(1,1-dibromomethylene)ferroceno[1,2-a]indene, (Z)-3-(1-bromomethylene)-6-iodoferroceno[1,2-a]indene, and benzo[5,6-f]ferroceno[2,3,a]inden-1-one. Any application-oriented design of chiral catalysts requires fundamental knowledge about the ligands involved, not only in terms of atom-connectivity, but also in terms of their three-dimensional structure and steric demand. Therefore, the crystal structures of 2-ferrocenylbenzoic acid, ferroceno[1,2-a]indene, and (Z)-3-(1-bromomethylene)-6-iodoferroceno[1,2-a]indene have been determined. The bond-lengths that can be retrieved therefrom also allow for an estimation of the reactivity of the aryl-iodo, bromo-methylidene and dibromomethylidene moieties. Crystals 2013-02-27 3 1 Article 10.3390/cryst3010141 141 148 2073-4352 2013-02-27 doi: 10.3390/cryst3010141 Klaus Wurst Gerhard Laus Michael Buchmeiser Herwig Schottenberger http://www.mdpi.com/2073-4352/3/1/120 In Raman spectroscopy of graphite and graphene, the D band at ∼ 1355 cm−1 is used as the indication of the dirtiness of a sample. However, our analysis suggests that the physics behind the D band is closely related to a very clear idea for describing a molecule, namely bonding and antibonding orbitals in graphene. In this paper, we review our recent work on the mechanism for activating the D band at a graphene edge. Crystals 2013-02-22 3 1 Article 10.3390/cryst3010120 120 140 2073-4352 2013-02-22 doi: 10.3390/cryst3010120 Ken-ichi Sasaki Yasuhiro Tokura Tetsuomi Sogawa http://www.mdpi.com/2073-4352/3/1/112 The synthesis, crystal structure, and conductivity of a solvent-included ternary charge-transfer salt (BEDT-TTF)2GaCl4(C6H5Cl)0.5 (1) is described and interpreted. Electrochemical oxidation of neutral bis(ethyelenedithio)-tetrathiafulvalene (BEDT-TTF) in the presence of (Me4N)Ga(C2O4)Cl2 in a mixture of C6H5Cl and C2H5OH yields crystals of 1. Compound 1 crystallized as a monoclinic C 2/c space group with cell parameters: a = 47.0615(4) Å, b = 6.7895(1) Å, c = 31.6297(4) Å, β = 132.064(1)°, V = 7503.0(2) Å3, Z = 8 at 293 K and a = 46.4767(5) Å, b = 6.7398(1) Å, c = 31.0778(4) Å, β = 131.630(1)°, V = 7267.4(2) Å3, Z = 8 at 120 K. The formal charge of the donor molecule was assigned as +0.5 from bond lengths in the TTF core. The donor molecules stack with C―···S contacts along the c direction and side-to-side S…S contacts along the b direction to form a two-dimensional donor layer on the bc plane. In the anion sheet, C6H5Cl chain is sandwiched by two GaCl4− chains with Cl…Cl contacts. Compound 1 shows semiconductive behavior with Ea = 124 meV between room-temperature and 150 K and σ300K = 1 S·cm−1. Crystals 2013-02-18 3 1 Communication 10.3390/cryst3010112 112 119 2073-4352 2013-02-18 doi: 10.3390/cryst3010112 Bin Zhang Yan Zhang http://www.mdpi.com/2073-4352/3/1/79 Graphene, a single atomic layer of graphite, has been a material of recent intensive studies due to its novel electronic and structural properties and its potential applications in the emerging area of carbon-based electronic devices. Metal on graphene growth is one of the current research interests, aiming at improving and manipulating the electronic and magnetic properties of graphene through metal atom adsorption or doping to meet various requirements in device applications. In this paper, we will give an overview of recent experimental and computational investigation of interaction, growth morphology, and thermal stability of various metals on graphene grown on 6H-SiC(0001) substrate. Crystals 2013-01-31 3 1 Review 10.3390/cryst3010079 79 111 2073-4352 2013-01-31 doi: 10.3390/cryst3010079 Xiaojie Liu Cai-Zhuang Wang Myron Hupalo Hai-Qing Lin Kai-Ming Ho Michael Tringides http://www.mdpi.com/2073-4352/3/1/49 Magnetically-doped graphene systems are potential candidates for application in future spintronic devices. A key step is to understand the pairwise interactions between magnetic impurities embedded in graphene that are mediated by the graphene conduction electrons. A large number of studies have been undertaken to investigate the indirect exchange, or RKKY (Ruderman-Kittel-Kasuya-Yosida), interactions in graphene. Many of these studies report a decay rate faster than expected for a two-dimensional material and the absence of the usual distance dependent oscillations. In this review we summarize the techniques used to calculate the interaction and present the key results obtained to date. The effects of more detailed parameterisations of the magnetic impurities and graphene host are considered, as are results obtained from ab initio calculations. Since the fast decay of the interaction presents an obstacle to spintronic applications, we focus in particular on the possibility of augmenting the interaction range by a number of methods including doping, spin precession and the application of strain. Crystals 2013-01-30 3 1 Review 10.3390/cryst3010049 49 78 2073-4352 2013-01-30 doi: 10.3390/cryst3010049 Stephen Power Mauro Ferreira http://www.mdpi.com/2073-4352/3/1/38 The combined effects of an asymmetric (square or V-shaped) notch and uniaxial strain are studied in a zigzag graphene nanoribbon (ZGNR) device using a generalized tight-binding model. The spin-polarization and conductance-gap properties, calculated within the Landauer–B¨uttiker formalism, were found to be tunable for uniaxial strain along the ribbon-length and ribbon-width for an ideal ZGNR and square (V-shaped) notched ZGNR systems. Uniaxial strain along the ribbon-width for strains 10% initiated significant notch-dependent reductions to the conduction-gap. For the V-shaped notch, such strains also induced spin-dependent changes that result, at 20% strain, in a semi-conductive state and metallic state for each respective spin-type, thus demonstrating possible quantum mechanisms for spin-filtration. Crystals 2013-01-23 3 1 Article 10.3390/cryst3010038 38 48 2073-4352 2013-01-23 doi: 10.3390/cryst3010038 Jack Baldwin Y. Hancock http://www.mdpi.com/2073-4352/3/1/28 Reduced graphene oxide–carbon nanotube (RGO–CNT) hybrid materials were prepared by a simple catalyst-free route. The thermostability, photoluminescence (PL) and electrical properties of RGO–CNTs were investigated systematically. The results revealed that compared to RGO, RGO–CNTs showed multicolor PL, and higher thermostability and conductivity. The RGO–CNTs therefore have important potential applications in the fields of photonic and electrical devices. Crystals 2013-01-21 3 1 Article 10.3390/cryst3010028 28 37 2073-4352 2013-01-21 doi: 10.3390/cryst3010028 Fuchi Liu Yong Cao Mingdong Yi Linghai Xie Wei Huang Nujiang Tang Wei Zhong Youwei Du http://www.mdpi.com/2073-4352/3/1/14 We study the bound state spectrum and the conditions for entering a supercritical regime in graphene with strong intrinsic and Rashba spin-orbit interactions within the topological insulator phase. Explicit results are provided for a disk-shaped potential well and for the Coulomb center problem. Crystals 2013-01-21 3 1 Article 10.3390/cryst3010014 14 27 2073-4352 2013-01-21 doi: 10.3390/cryst3010014 Denis Klöpfer Alessandro De Martino Reinhold Egger http://www.mdpi.com/2073-4352/3/1/1 Graphene grown on C-face SiC substrates using two procedures, high and low growth temperature and different ambients, was investigated using Low Energy Electron Microscopy (LEEM), X-ray Photo Electron Electron Microscopy (XPEEM), selected area Low Energy Electron Diffraction (μ-LEED) and selected area Photo Electron Spectroscopy (μ-PES). Both types of samples showed formation of μm-sized grains of graphene. The sharp (1 × 1) μ-LEED pattern and six Dirac cones observed in constant energy photoelectron angular distribution patterns from a grain showed that adjacent layers are not rotated relative to each other, but that adjacent grains in general have different azimuthal orientations. Diffraction spots from the SiC substrate appeared in μ-LEED patterns collected at higher energies, showing that the rotation angle between graphene and SiC varied. C 1s spectra collected did not show any hint of a carbon interface layer. A hydrogen treatment applied was found to have a detrimental effect on the graphene quality for both types of samples, since the graphene domain/grain size was drastically reduced. From hydrogen treated samples, μ-LEED showed at first a clear (1 × 1) pattern, but within minutes, a pattern containing strong superstructure spots, indicating the presence of twisted graphene layers. The LEED electron beam was found to induce local desorption of hydrogen. Heating a hydrogenated C-face graphene sample did not restore the quality of the original as-grown sample. Crystals 2013-01-15 3 1 Article 10.3390/cryst3010001 1 13 2073-4352 2013-01-15 doi: 10.3390/cryst3010001 Leif Johansson Chao Xia Jawad Hassan Tihomir Iakimov Alexei Zakharov Somsakul Watcharinyanon Rositza Yakimova Erik Janzén Chariya Virojanadara http://www.mdpi.com/2073-4352/2/4/1502 The metallic state of the molecular conductor β-(meso-DMBEDT-TTF)2X (DMBEDT-TTF = 2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-ylidene)-5,6-dihydro-5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin, X = PF6, AsF6) is transformed into the checkerboard-type charge-ordered state at around 75–80 K with accompanying metal-insulator (MI) transition on the anisotropic triangular lattice. With lowering temperatures, the magnetic susceptibility decreases gradually and reveals a sudden drop at the MI transition. By applying pressure, the charge-ordered state is suppressed and superconductivity appears in β-(meso-DMBEDT-TTF)2AsF6 as well as in the reported β-(meso-DMBEDT-TTF)2PF6. The charge-ordered spin-gapped state and the pressure-induced superconducting state are discussed through the paired-electron crystal (PEC) model, where the spin-bonded electron pairs stay and become mobile in the crystal, namely the valence-bond solid (VBS) and the resonant valence bonded (RVB) state in the quarter-filled band structure. Crystals 2012-11-29 2 4 Article 10.3390/cryst2041502 1502 1513 2073-4352 2012-11-29 doi: 10.3390/cryst2041502 Takahisa Shikama Tatsuya Shimokawa Sanguchul Lee Takayuki Isono Akira Ueda Kazuyuki Takahashi Akiko Nakao Reiji Kumai Hironori Nakao Kensuke Kobayashi Youichi Murakami Motoi Kimata Hiroyuki Tajima Kazuyuki Matsubayashi Yoshiya Uwatoko Yutaka Nishio Koji Kajita Hatsumi Mori http://www.mdpi.com/2073-4352/2/4/1492 The crystal structures of 1-hydroxyimidazole and four protic salts (chloride, bromide, sulfate, nitrate) thereof were determined. The molecular geometries (bond lengths and angles) of the free base and the salts were compared. Hydrogen bonding patterns were studied, and OH…N, OH…Cl, OH…Br, OH…O, NH…Cl, NH…Br, and NH…O interactions were identified. Hirshfeld surface analysis gave quantitative insight into these interactions. Crystals 2012-10-31 2 4 Article 10.3390/cryst2041492 1492 1501 2073-4352 2012-10-31 doi: 10.3390/cryst2041492 Gerhard Laus Volker Kahlenberg http://www.mdpi.com/2073-4352/2/4/1483 The photonic bands of various TiO2 2D photonic crystals, i.e., cylindrical, square and hexagonal columns connected with/without walls and filled with acetonitrile, were investigated from the perspective of dye-sensitized solar cells. The finite-difference time-domain methods revealed that two-dimensional (2D) photonic crystals with rods connected with walls composed of TiO2 and electrolytes had complete photonic band gaps under specific conditions. This optimally designed bandgap reaches a large Δω/ωmid value, 1.9%, in a triangular array of square rods connected with walls, which is the largest complete 2D bandgap thus far reported for a photochemical system. These discoveries would promote the photochemical applications of photonic crystals. Crystals 2012-10-26 2 4 Communication 10.3390/cryst2041483 1483 1491 2073-4352 2012-10-26 doi: 10.3390/cryst2041483 Sachiko Matsushita Mikiro Hayashi Toshihiro Isobe Akira Nakajima http://www.mdpi.com/2073-4352/2/4/1460 Pressure is a powerful tool to unveil the profound nature of electronic properties in a variety of organic conductors. Starting from technology of high pressure, we plan to review what kind of physics or phenomena have previously been discussed. Crystals 2012-10-23 2 4 Review 10.3390/cryst2041460 1460 1482 2073-4352 2012-10-23 doi: 10.3390/cryst2041460 Keizo Murata Keiichi Yokogawa Sonachalam Arumugam Harukazu Yoshino http://www.mdpi.com/2073-4352/2/4/1455 An improved synthesis of the Cholesteryl Ester Transfer Protein inhibitor dalcetrapib is reported. The precursor disulfide was reduced (a) by Mg/MeOH or (b) by EtSH/DBU/THF. The resulting thiol was acylated (a) by a known procedure or (b) in a one-pot process. Impurities were removed (a) by dithiothreitol (DTT) or (b) by oxidation using H2O2. Dalcetrapib crystallized in space group P21/c. Crystals 2012-10-19 2 4 Article 10.3390/cryst2041455 1455 1459 2073-4352 2012-10-19 doi: 10.3390/cryst2041455 Gerhard Laus Volker Kahlenberg Frank Richter Sven Nerdinger Herwig Schottenberger http://www.mdpi.com/2073-4352/2/4/1441 The absolute configuration and structure of aegelinol, a pyranocoumarin isolated from Ferulago asparagifolia Boiss (Apiaceae), has been determined by crystallography. Crystal structure of the inclusion complex of aegelinol in β-cyclodextrin was determined (a = 15.404(1) Å, b = 15.281(1) Å, c = 17.890(1) Å, α = 99.662(1), β = 113.4230(1), γ = 102.481(1)°, P1; R1 = 6.71%) and allowed unambiguous determination of the absolute configuration of the stereogenic center of aegelinol. The pyranocoumarin guest is included within the cylindrical cavity formed by dimeric β-cyclodextrin molecules with a head-to-head arrangement. Crystal structure of aegelinol alone was also determined (a = 6.8921(3) Å, b = 11.4302(9) Å, c = 44.964(3) Å, P212121; R1 = 4.44%) and allowed precise determination of its geometry. Aegelinol crystallizes with three molecules in the asymmetric unit held together by H-bonds and π-stacking interactions. Crystals 2012-10-17 2 4 Article 10.3390/cryst2041441 1441 1454 2073-4352 2012-10-17 doi: 10.3390/cryst2041441 Kossay Elasaad Racha Alkhatib Thierry Hennebelle Bernadette Norberg Johan Wouters http://www.mdpi.com/2073-4352/2/4/1434 Piperidinium copper(I) bromide, (C5H12N)Cu2Br3, was obtained from a solution of CuBr2, piperidine, and HBr in ethanol. At 60 °C ethanol slowly reduces copper(II) to copper(I). Colorless plates of (C5H12N)Cu2Br3 crystallize in the triclinic space group P-1 with lattice parameters of a = 6.2948(10) Å, b = 8.2624(14) Å, c = 10.7612(17) Å, α = 75.964(19)°, β = 89.232(19)°, γ = 84.072(19)°, and Z = 2 at 173 K. [CuBr4] tetrahedra share edges and form [Cu2Br3]− ladders parallel to the a-axis. (C5H12N)+ ions adopt a chair conformation and connect the [Cu2Br3]− ladders via H-bonding. The (C5H12N)Cu2Br3 structure is related to the mineral rasvumite, KFe2S3, space group Cmcm, which is isostructural to several alkali copper(I) halides. Crystals 2012-10-16 2 4 Article 10.3390/cryst2041434 1434 1440 2073-4352 2012-10-16 doi: 10.3390/cryst2041434 Theresa Komm Daniel Biner Antonia Neels Karl W. Krämer http://www.mdpi.com/2073-4352/2/4/1410 As potential hydrogen storage media, magnesium based hydrides have been systematically studied in order to improve reversibility, storage capacity, kinetics and thermodynamics. The present article deals with the electrochemical and optical properties of Mg alloy hydrides. Electrochemical hydrogenation, compared to conventional gas phase hydrogen loading, provides precise control with only moderate reaction conditions. Interestingly, the alloy composition determines the crystallographic nature of the metal-hydride: a structural change is induced from rutile to fluorite at 80 at.% of Mg in Mg-TM alloy, with ensuing improved hydrogen mobility and storage capacity. So far, 6 wt.% (equivalent to 1600 mAh/g) of reversibly stored hydrogen in MgyTM(1-y)Hx (TM: Sc, Ti) has been reported. Thin film forms of these metal-hydrides reveal interesting electrochromic properties as a function of hydrogen content. Optical switching occurs during (de)hydrogenation between the reflective metal and the transparent metal hydride states. The chronological sequence of the optical improvements in optically active metal hydrides starts with the rare earth systems (YHx), followed by Mg rare earth alloy hydrides (MgyGd(1-y)Hx) and concludes with Mg transition metal hydrides (MgyTM(1-y)Hx). In-situ optical characterization of gradient thin films during (de)hydrogenation, denoted as hydrogenography, enables the monitoring of alloy composition gradients simultaneously. Crystals 2012-10-15 2 4 Review 10.3390/cryst2041410 1410 1433 2073-4352 2012-10-15 doi: 10.3390/cryst2041410 Thirugnasambandam G. Manivasagam Kamil Kiraz Peter H. L. Notten http://www.mdpi.com/2073-4352/2/4/1393 Properties of strontium tetraborate (SBO) and features of as-grown anti-parallel domains are summarized. From the point of view of nonlinear optics, these domains form nonlinear photonic crystals (NPC). Applications of NPC to the deep ultraviolet generation and fs pulse diagnostics are described. NPC and SBO are prospective media for the creation of a widely tunable source of fs pulses in the vacuum ultraviolet and for autocorrelation diagnostics of broadly tunable sources. Crystals 2012-10-01 2 4 Review 10.3390/cryst2041393 1393 1409 2073-4352 2012-10-01 doi: 10.3390/cryst2041393 Aleksandr S. Aleksandrovsky Andrey M. Vyunishev Alexandre I. Zaitsev http://www.mdpi.com/2073-4352/2/4/1382 We examined optical fibers suitable for avoiding such problems as the fiber fuse phenomenon and failures at bends with a high power input. We found that the threshold power for fiber fuse propagation in photonic crystal fiber (PCF) and hole-assisted fiber (HAF) can exceed 18 W, which is more than 10 times that in conventional single-mode fiber (SMF). We considered this high threshold power in PCF and HAF to be caused by a jet of high temperature fluid penetrating the air holes. We showed examples of two kinds of failures at bends in conventional SMF when the input power was 9 W. We also observed the generation of a fiber fuse under a condition that caused a bend-loss induced failure. We showed that one solution for the failures at bends is to use optical fibers with a low bending loss such as PCF and HAF. Therefore, we consider PCF and HAF to be attractive solutions to the problems of the fiber fuse phenomenon and failures at bends with a high power input. Crystals 2012-09-28 2 4 Article 10.3390/cryst2041382 1382 1392 2073-4352 2012-09-28 doi: 10.3390/cryst2041382 Kenji Kurokawa http://www.mdpi.com/2073-4352/2/4/1374 The three dimensional bismuth ethanedisulfonate framework Bi(O3SC2H4SO3)1.5(H2O)2 was synthesized under hydrothermal conditions using the bidentate ligand 1,2-ethanedisulfonate and then characterized through X-ray diffraction and elemental analyses. The bismuth cation coordinates at three different ethanedisulfonate ligands and has a coordination number of eight, which is accompanied by a distorted square antiprismatic configuration. Here, we report on the crystal structure of this bismuth metal–organic framework and its coordination behavior, which has thus far not been reported in heavier main group elements. Crystals 2012-09-28 2 4 Communication 10.3390/cryst2041374 1374 1381 2073-4352 2012-09-28 doi: 10.3390/cryst2041374 Fabienne Gschwind Martin Jansen http://www.mdpi.com/2073-4352/2/4/1366 The synthesis and crystal structure of the one-dimensional coordination polymer, [Cd(spar)2]n·n(H2O), are described, where spar− is the sparfloxacinate anion, C19H21N4O3F2−. The Cd2+ ion is bonded to four spar− ligands: Two O,O-chelate with their β-keto carboxylate groupings and two are monodentate-bound through a carboxylate O atom, to result in a distorted CdO6 octahedral coordination geometry. The bridging ligands lead to [100] polymeric chains in the crystal and N–H···O hydrogen bonds and possible weak aromatic p–p stacking interactions help to consolidate the structure. Crystal data: C38H44CdF4N8O7, Mr = 913.21, triclinic, (No. 2), Z = 2, a = 9.2256(4) Å, b = 12.8767(5) Å, c = 17.4297(7) Å, α = 89.505(2)°, β = 85.062(2)°, g = 70.757(2)°, V = 1947.20(14) Å3, R(F) = 0.036, wR(F2) = 0.082. Crystals 2012-09-28 2 4 Short Note 10.3390/cryst2041366 1366 1373 2073-4352 2012-09-28 doi: 10.3390/cryst2041366 Zhe An Jing Gao William T. A. Harrison http://www.mdpi.com/2073-4352/2/3/1357 Two dinuclear CuII complexes based on a diazecine ligand were characterized by X-ray diffraction, one of which includes the rare CuII–F bond, resulting from dissociation of a BF4− ion. The F− ligands actively participate in the crystal structure, behaving as acceptors for hydrogen bonding. Crystals 2012-09-18 2 3 Article 10.3390/cryst2031357 1357 1365 2073-4352 2012-09-18 doi: 10.3390/cryst2031357 Juan Olguín Sylvain Bernès Laura Gasque http://www.mdpi.com/2073-4352/2/3/1347 5-(2-Chlorophenyl)-7-ethyl-1H-thieno[2,3-e][1,4]diazepin-2(3H)-one, a close analogue of clotiazepam (full agonist at GABA receptor), crystallizes in monoclinic P21/c space group with a = 15.6941(6) Å, b = 10.7909(4) Å, c = 8.6586(3) Å, and β = 102.184(4)° (at 125 K). Seven-Membered diazepine ring has approximate mirror plane of symmetry, planar thieno and phenyl rings are almost perpendicular to one another, dihedral angle between their mean planes is 84.11(5)°. N–H···O hydrogen bonds connect molecules into centrosymmetric dimers which are further expanded into 3D crystal structure with the help of weaker C–H···O and C–H···π interactions. The methyl group is disordered at room temperature, but it gets gradually ordered at lower temperatures and becomes fully ordered at approximately 200 K. The changes in structure with temperature were studied between 125 and 380 K. The unit cell volume—as expected—increases almost monotonically when the temperature rises, but one of the parameters shortens significantly. Crystals 2012-09-18 2 3 Article 10.3390/cryst2031347 1347 1356 2073-4352 2012-09-18 doi: 10.3390/cryst2031347 Grzegorz Dutkiewicz Maciej Kubicki Alaloor S. Dayananda Hemmige S. Yathirajan Andagar R. Ramesha http://www.mdpi.com/2073-4352/2/3/1291 This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF)2X, and α-(BEDT-TTF)2X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a charge-ordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN)4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I3 salt. In α-(BEDT-TTF)2I3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρmax~0.6) at low temperature. The long-range charge-ordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDT-TTF)2MHg(SCN)4 (X = NH4, K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH4 salt. α′-(BEDT-TTF)2IBr2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρmax~0.8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. Crystals 2012-09-18 2 3 Review 10.3390/cryst2031291 1291 1346 2073-4352 2012-09-18 doi: 10.3390/cryst2031291 Kyuya Yakushi http://www.mdpi.com/2073-4352/2/3/1283 The compound τ-(P-S,S-DMEDT-TTF)2(AuCl2) (AuCl2)y (where P-S,S-DMEDT-TTF is the compound pyrazino-(S,S)-dimethyl-ethylenedithio-tetrathiofulvale) crystallizes in the non-centrosymmetric space group I-42d, with a = 7.3260(1) Å and c = 67.5487(12) Å (RT data) and remains tetragonal in the temperature range from RT to 100 K. This compound is a quasi-two-dimensional material and the relation of the lattice of the order part of the structure created by the donor molecules with that of the disordered anion lattice revealed by intense diffusion streaks give a value of y ≈ 0.9. In contrast to the Br and I analogs or the related compounds which contain the compound ethylenedioxy-S,S-dimethylenedithiotetrathiafulvalene (abbreviated as EDO-S,S-DMEDT-TTF) as donor and which exhibit anisotropic metallic behavior down to low temperature, this compound is anisotropic semiconductor in the same temperature range. The appearance of satellites on the diffraction images recorded below 110 K indicates a structural change. Resistivity measurements show that this material is a semiconductor with anisotropy σa/σc of ca. 400–1400 at room temperature. Crystals 2012-09-03 2 3 Article 10.3390/cryst2031283 1283 1290 2073-4352 2012-09-03 doi: 10.3390/cryst2031283 Vassilis Psycharis George A. Mousdis Keizo Murata George C. Papavassiliou http://www.mdpi.com/2073-4352/2/3/1261 An approach to various metal hydrides based on electronic principles is presented. The effective medium theory (EMT) is used to illustrate fundamental aspects of metal-hydrogen interaction and clarify the most important processes taking place during the interaction. The elaboration is extended using the numerous existing results of experiment and calculations, as well as using some new material. In particular, the absorption/desorption of H in the Mg/MgH2 system is analyzed in detail, and all relevant initial structures and processes explained. Reasons for the high stability and slow sorption in this system are noted, and possible solutions proposed. The role of the transition-metal impurities in MgH2 is briefly discussed, and some interesting phenomena, observed in complex intermetallic compounds, are mentioned. The principle mechanism governing the Li-amide/imide transformation is also discussed. Latterly, some perspectives for the metal-hydrides investigation from the electronic point of view are elucidated. Crystals 2012-08-30 2 3 Review 10.3390/cryst2031261 1261 1282 2073-4352 2012-08-30 doi: 10.3390/cryst2031261 Nenad Ivanović Nikola Novaković Ivana Radisavljević Ljiljana Matović Jasmina Grbović Novaković http://www.mdpi.com/2073-4352/2/3/1253 The synthesis, structure and some properties of the one-dimensional coordination polymer, [Pr2(pdc)3(Hpdc)]n·n(H3hp)·8n(H2O), (H2pdc = pyridine 2,6-dicarboxylic acid, C7H5NO4; 3hp = 3-hydroxypyridine, C5H5NO) are described. One of the Pr3+ ions is coordinated by two O,N,O-tridentate pdc2− ligands and one tridentate Hpdc− anion to generate a fairly regular PrO6N3 tri-capped trigonal prism, with the N atoms acting as the caps. The second Pr3+ ion is coordinated by one tridentate pdc2− dianion, four water molecules and two monodentate bridging pdc2− ligands to result in a PrO8N coordination polyhedron that approximates to a mono-capped square-anti-prism. The ligands bridge the metal-atom nodes into a chain, which extends in the [100] direction. The H3hp+ cation and uncoordinated water molecules occupy the inter-chain regions and an N–HLO and numerous O–HLO hydrogen bonds consolidate the structure. The H3hp+ species appears to intercalate between pendant pdc rings to consolidate the polymeric structure. Crystal data: 1 (C33H43N5O29Pr2), Mr = 1255.54, triclinic, (No. 2), Z = 2, a = 13.2567(1) Å, b = 13.6304(2) Å, c = 13.6409(2) Å, α = 89.695(1)°, β = 63.049(1)°, γ = 86.105(1)°, V = 2191.16(5) Å3, R(F) = 0.033, wR(F2) = 0.084. Crystals 2012-08-27 2 3 Short Note 10.3390/cryst2031253 1253 1260 2073-4352 2012-08-27 doi: 10.3390/cryst2031253 Shahzad Sharif Onur Sahin Islam Ullah Khan Orhan Büyükgüngör William T. A. Harrison http://www.mdpi.com/2073-4352/2/3/1248 The title compound, Methyl 5-Hydroxy-1-Phenyl-1H-Pyrazole-3-Carboxylate (C11H10N2O3), was prepared by a one-pot, two-component reaction of an equimolar mixture of phenyl hydrazine and dimethyl acetylene dicarboxylate (DMAD) at reflux temperature for 2 h in a mixture of toluene and dichloromethane as solvent. C11H10N2O3 was crystallized from an ethanol solution in monoclinic space group P21/c with unit cell dimensions a = 9.5408(16), b = 9.5827(16), c = 11.580(2) Å, β = 105.838(3)°, V = 1018.5(3) Å3, Z = 4. Crystals 2012-08-27 2 3 Short Note 10.3390/cryst2031248 1248 1252 2073-4352 2012-08-27 doi: 10.3390/cryst2031248 Aamer Saeed Ifzan Arshad Ulrich Flörke http://www.mdpi.com/2073-4352/2/3/1239 The crystal and molecular structures of the title compounds, ethyl 4-(4-hydroxyphenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (I) and ethyl 4-(3-bromophenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (II), are reported and confirmed by single crystal X-ray diffraction data. Compound (I), C26H24O5, crystallizes from a methanol solution in the monoclinic C2/c space group with eight molecules in the unit cell. The unit cell parameters are: a = 25.4114(5) Å, b = 8.47440(10) Å, c = 20.6921(4) Å, β = 108.328(2)° and V = 4229.92(13) Å3. Disorder is observed throughout the entire molecule with an occupancy ratio 0.690(2):0.310(2). Compound (II), C26H23O4Br, crystallizes from an ethyl acetate solution in the monoclinic P21/c spacegroup with four molecules in the unit cell. The unit cell parameters are a = 17.8991(9) Å, b = 11.4369(6) Å, c = 10.8507(5) Å, β = 92.428(4)° and V = 2219.25(19) Å3. Disorder is observed in the cyclohexenone ring and the carboxylate group with an occupancy ratio 0.830(6):0.170(6). Weak O–H...O (I) or C–H...O (II) intermolecular interactions are observed which influence crystal packing stability. These chalcone derivative types of molecules are important in their ability to act as activated unsaturated systems in conjugated addition reactions of carbanions in the presence of basic catalysts which exhibit a multitude of biological activities. Crystals 2012-08-27 2 3 Article 10.3390/cryst2031239 1239 1247 2073-4352 2012-08-27 doi: 10.3390/cryst2031239 Manpreet Kaur Jerry P. Jasinski Ray J. Butcher Hemmige S. Yathirajan Anil N. Mayekar Badiadka Narayana http://www.mdpi.com/2073-4352/2/3/1222 Tetrathiafulvalene (TTF), pentacene, and quarterthiophene with tert-butyl substituents are synthesized, and the crystal structures and the transistor properties are investigated. The tetracyanoquinodimethane (TCNQ) complex of tert-butyl TTF constructs highly one-dimensional segregated columns with tetragonal crystal symmetry. Crystals 2012-08-22 2 3 Article 10.3390/cryst2031222 1222 1238 2073-4352 2012-08-22 doi: 10.3390/cryst2031222 Toshiki Higashino Yuto Akiyama Hirotaka Kojima Tadashi Kawamoto Takehiko Mori http://www.mdpi.com/2073-4352/2/3/1210 We have studied the electronic structure of Cu(tmdt)2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM) exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt)2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(−) band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt)2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt)2 and Cu(dmdt)2. Crystals 2012-08-21 2 3 Article 10.3390/cryst2031210 1210 1221 2073-4352 2012-08-21 doi: 10.3390/cryst2031210 Shoji Ishibashi Kiyoyuki Terakura http://www.mdpi.com/2073-4352/2/3/1201 The conversion of Z-phenylalanine hydrazide with cyanogen bromide resulted in the formation of the corresponding 2-amino-1,3,4-oxadiazole by spontaneous cyclization of the intermediary cyanohydrazide. The molecular structure of the product was confirmed by single crystal X-ray diffraction. Crystals of the title compound where obtained from a saturated solution in a mixture of petroleum ether and ethyl acetate and belong to the monoclinic space group P21 with unit cell parameters a = 9.8152(2) Å, b = 9.6305(2) Å, c = 9.8465(2) Å, β = 116.785(1)°. The asymmetric unit contains one molecule. Crystals 2012-08-20 2 3 Communication 10.3390/cryst2031201 1201 1209 2073-4352 2012-08-20 doi: 10.3390/cryst2031201 Reik Löser Martin Nieger Michael Gütschow http://www.mdpi.com/2073-4352/2/3/1155 Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration. Crystals 2012-08-20 2 3 Review 10.3390/cryst2031155 1155 1200 2073-4352 2012-08-20 doi: 10.3390/cryst2031155 Chisa Hotta http://www.mdpi.com/2073-4352/2/3/1146 The crystal structure of APA2[Zn3(HPO4)4(H2O)2] (APA = 2-amino-1-phenylene-ammonium, C6H9N2+) (1), as prepared by a predominantly non-aqueous synthesis, is described and compared to related compounds. 1 is built up from an alternating array of ZnO4 and HPO4 tetrahedra sharing vertices as Zn–O–P bonds to generate infinite anionic sheets. Within these sheets, polyhedral 4-, 6- and 8-rings are apparent. The negative charge of the inorganic layer is balanced by singly-protonated APA template cations and water molecules are also present. The components are linked by Nt–H⋯Of, Of–H⋯Ow, Ow–H⋯Of and Of–H⋯Nt (t = template, f = framework, w = water) hydrogen bonds: the last of these represents an unusual framework-to-template interaction. Weak Ct–H⋯Of links may also play a role in consolidating the structure. Crystal data: 1 (C12H26N4O18P4Zn3), Mr = 834.36, monoclinic, C2/c (No. 15), Z = 4, a = 20.194 (8) Å, b = 8.682 (3) Å, c = 15.123 (6) Å, β = 91.510 (11)°, V = 2650.5 (17) Å3, R(F) = 0.048, wR(F2) = 0.112. Crystals 2012-08-16 2 3 Short Note 10.3390/cryst2031146 1146 1154 2073-4352 2012-08-16 doi: 10.3390/cryst2031146 Joel C. Aughey William T. A. Harrison Alexandra M. Z. Slawin http://www.mdpi.com/2073-4352/2/3/1136 Single crystals and phase pure samples of oxygen-poor ternary lanthanide oxide selenides with the composition M10OSe14 (M = La–Nd; tetragonal, I41/acd; a = 1592.0–1559.8 pm, c = 2106.5–2062.9 pm) could be obtained by reacting the corresponding metals, selenium and selenium dioxide as oxygen source. Their crystal structures are isotypic with Pr10OS14 and thus contain isolated [OM4]10+ tetrahedra (d(O2––M3+) = 243–248 pm) embedded in a complex anionic {[M6Se14]10–} lanthanide selenide matrix (d(M3+–Se2–) = 288–358 pm). All three crystallographically independent M3+ cations exhibit eight contacts to chalcogenide anions (O2– and/or Se2–) resulting in the formation of bicapped trigonal prismatic coordination polyhedra. The optical band gaps of the oxide selenides M10OSe14 amount to values between 1.89 and 2.04 eV indicating wide band-gap semiconductors. Crystals 2012-08-16 2 3 Article 10.3390/cryst2031136 1136 1145 2073-4352 2012-08-16 doi: 10.3390/cryst2031136 Frank A. Weber Christian M. Schurz Susanne Frunder Charlotte F. Kuhn Thomas Schleid http://www.mdpi.com/2073-4352/2/3/1116 1H and 195Pt NMR are used to probe the spin ½ anion chain in the quasi-one-dimensional conductor Per2[Pt(mnt)2], which exhibits nearly simultaneous charge density wave (CDW) and spin-Peierls (SP) transitions at low temperatures (Tc ~ 8 K). Below Tc the [Pt(mnt)2] chain forms a spin-singlet state that is evident in 1H NMR spectra and spin relaxation (1/T1) rates; however minority unpaired Pt spins may remain in the SP ground state. With increasing magnetic field, the SP and CDW order parameters decrease in unison, indicating they are coupled up to a critical field Bc ~ 20 T. Above Bc, the spin singlet evolves into a spin-polarized configuration. The 195Pt NMR signals vanish as either Tc or Bc are approached from within the SP ground state, suggesting the hyperfine field of the Pt nucleus is significantly stronger than at the proton sites. Simulations yield a consistent picture of the angular, temperature, and magnetic field-dependent spectral features. Crystals 2012-08-16 2 3 Review 10.3390/cryst2031116 1116 1135 2073-4352 2012-08-16 doi: 10.3390/cryst2031116 Elizabeth L. Green Lloyd L. Lumata James S. Brooks Phil Kuhns Arneil Reyes Stuart E. Brown Manuel Almeida http://www.mdpi.com/2073-4352/2/3/1108 Two new pyrazoline derivatives, 3,5-bis(4-fluorophenyl)-4,5-dihydropyrazole-1-carboxamide (1) and 3,5-bis(4-fluorophenyl)-4,5-dihydropyrazole-1-carbothioamide (2), were synthesized by reacting 4,4'-difluoro chalcone with semicarbazide hydrochloride and thiosemicarbazide in ethanolic sodium hydroxide solution. Both the compounds were confirmed by single crystal X-ray diffraction data and supported by IR, NMR, and mass spectral data. In 1, crystal packing is stabilized by N–H…O hydrogen bonds and weak N–H...N, N–H…F and C–H…F intermolecular interactions. In 2, only weak N–H…F and N–H…S intermolecular interactions are observed. Crystal data: C16H13F2N3O, (1), Mr = 301.29, monoclinic, C2/c, a = 17.6219(6) Å, b = 10.8735(3) Å, c = 15.3216(5) Å, β = 102.864(3)°, V = 2862.11(16) Å3, Z = 8, T = 173 K, R(F) = 0.0511, wR(F2) = 0.1333; C16H13F2N3S, (2), Mr = 317.35, monoclinic, P21/c, a = 14.339(2) Å, b = 11.1478(17) Å, c = 9.541(2)(5) Å, β = 107.007(18)°, V = 1458.5(5) Å3, Z = 4, T = 173 K, R(F) = 0.0413, wR(F2) = 0.0959. Crystals 2012-08-15 2 3 Article 10.3390/cryst2031108 1108 1115 2073-4352 2012-08-15 doi: 10.3390/cryst2031108 Jerry P. Jasinski James A. Golen Seranthimata Samshuddin Badiadka Narayana Hemmige S. Yathirajan http://www.mdpi.com/2073-4352/2/3/1092 Bis-fused donors composed of (thio)pyran-4-ylidene-1,3-dithiole and tetraselenafulvalene (1a, 2a) and their bis(methylthio) derivatives (1b, 2b) were synthesized. Cyclic voltamograms of all the donors consisted of four pairs of one-electron redox waves, and it was suggested that a positive charge of 1+• and 2+• distributed mainly on the (thio)pyran-4-ylidene-1,3-dithiole moiety. X-ray structure analysis revealed that (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) formed one-dimensional conducting stacks in which the donors were dimerized or tetramerized. In those salts, intramolecular charge disproportionation of the donors was suggested by X-ray structure analysis and density functional theory (DFT) calculation with UB3LYP/6-31G(d) basis function. A tight-binding band calculation suggested that these materials were band insulators. All the donors gave highly conducting TCNQ (7,7,8,8-tetracyanoquinodimethane) complexes and I3− salts (σrt = 0.3–19 S cm−1 on a compressed pellet) with very low activation energies of 0.017–0.040 eV, while single crystals of (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) exhibited semiconductive behavior with large activation energies (Ea = 0.16–0.22 eV). Crystals 2012-08-09 2 3 Article 10.3390/cryst2031092 1092 1107 2073-4352 2012-08-09 doi: 10.3390/cryst2031092 Ken-ichi Ishidzu Minoru Ashizawa Masaki Watanabe Takashi Shirahata Yohji Misaki http://www.mdpi.com/2073-4352/2/3/1084 The synthesis, structure and properties of the bimetallic layered coordination polymer, [KDy(C8H3NO6)3(C8H5NO6)]n·2n(C10H9N2)·5n(H2O) = [KDy(Hptc)3(H3ptc)]n·2n(Hbipy)·5n(H2O), are described. The Dy3+ ion is coordinated by three O,N,O-tridentate doubly-deprotonated pyridine tri-carboxylate (Hptc) ligands to generate a fairly regular DyO6N3 tri-capped trigonal prism, with the N atoms acting as the caps. The potassium ion is coordinated by an O,N,O-tridentate H3ptc molecule as well as monodentate and bidentate Hptc ligands to result in an irregular KNO9 coordination geometry. The ligands bridge the metal-atom nodes into a bimetallic, layered, coordination polymer, which extends as corrugated layers in the (010) plane, with the mono-protonated bipyridine cations and water molecules occupying the inter-layer regions: Unlike related structures, there are no dysprosium–water bonds. Many O–HLO and N–HLO hydrogen bonds consolidate the structure. Characterization and bioactivity data are described. Crystal data: C52H42DyKN8O29, Mr = 1444.54, triclinic, (No. 2), Z = 2, a = 9.188(2) Å, b = 15.7332(17) Å, c = 19.1664(19) Å, α = 92.797(6)°, β = 92.319(7)°, γ = 91.273(9)°, V = 2764.3(7) Å3, R(F) = 0.029, wR(F2) = 0.084. Crystals 2012-08-03 2 3 Short Note 10.3390/cryst2031084 1084 1091 2073-4352 2012-08-03 doi: 10.3390/cryst2031084 Shoaib Anwar Irfana Mariam Islam Ullah Khan Ejaz William T. A. Harrison Sohail Anwar http://www.mdpi.com/2073-4352/2/3/1067 Strongly electron-lattice- and electron-electron-correlated molecular crystals, such as charge transfer (CT) complexes, are often sensitive to external stimuli, e.g., photoexcitation, due to the cooperative or competitive correlation of various interactions present in the crystals. These crystals are thus productive targets for studying photoinduced phase transitions (PIPTs). Recent advancements in research on the PIPT of CT complexes, especially Et2Me2Sb[Pd(dmit)2]2 and (EDO-TTF)2PF6, are reviewed in this report. The former exhibits a photoinduced insulator-to-insulator phase transition with clearly assigned spectral change. We demonstrate how to find the dynamics of PIPT using this system. The latter exhibits a photoinduced hidden state as an initial PIPT process. Wide energy ranged time-resolved spectroscopy can probe many kinds of photo-absorption processes, i.e., intra-molecular and inter-molecular electron excitations and intramolecular and electron-molecular vibrations. The photoinduced spectral changes in these photo-absorption processes reveal various aspects of the dynamics of PIPT, including electronic structural changes, lattice structural changes, and molecular deformations. The complexities of the dynamics of the latter system were revealed by our measurements. Crystals 2012-07-27 2 3 Review 10.3390/cryst2031067 1067 1083 2073-4352 2012-07-27 doi: 10.3390/cryst2031067 Tadahiko Ishikawa Ken Onda Shin-ya Koshihara http://www.mdpi.com/2073-4352/2/3/1058 The crystal and molecular structures of two 2-aminothiophene derivatives, potential allosteric enhancers at the human A1 adenosine receptor, are reported. (2-Amino-4,5,6,7-tetrahydro-1-benzothiophen-3-yl)(phenyl)methanone (1) crystallizes in the orthorhombic space group Pna21 (a = 9.2080(4) Å, b = 14.0485(7) Å, c = 10.3826(6) Å), and (2-amino-5-ethylthiophen-3-yl)(2-chlorophenyl)methanone (2) crystalizes in the monoclinic P21/c space group with unit cell parameters a = 10.6092(8) Å, b = 10.8355(8) Å, c = 11.1346(9) Å, β = 98.643(6)Å. In both molecules the intramolecular N–H···O=C hydrogen bonds close six-membered planar rings and significantly influence the molecular conformation. Intermolecular N–H···O bonds connect the molecules in infinite chains along a in case of 1, and along b in 2; in each case the appropriate unit cell axis is approximately 10 Å long. Crystals 2012-07-27 2 3 Article 10.3390/cryst2031058 1058 1066 2073-4352 2012-07-27 doi: 10.3390/cryst2031058 Maciej Kubicki Grzegorz Dutkiewicz Hemmige S. Yathirajan Pankaj Dawar Andagar R. Ramesha Alaloor S. Dayananda http://www.mdpi.com/2073-4352/2/3/1034 Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetra-selena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of 13C-NMR studies have been performed of the double-site central 13C=13C bond substituted molecules. However, problems with the coupled spin system of 13C=13C complicated the interpretation for observations on NMR. Therefore, single-site 13C-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site 13C-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of 13C-NMR of the single-site 13C-susbstituted molecule utilizing the hyperfine coupling tensor. Crystals 2012-07-27 2 3 Review 10.3390/cryst2031034 1034 1057 2073-4352 2012-07-27 doi: 10.3390/cryst2031034 Shinji Hirose Masaki Misawa Atsushi Kawamoto http://www.mdpi.com/2073-4352/2/3/1017 The crystal structures of 2,4,5-tribromo-1-(prop-2-ynyl)imidazole and seven new 1,3-dialkyl-2,4,5-tribromoimidazolium salts (R1 = propenyl, propynyl, dibromopropenyl; R2 = Me, Et) with halogen-containing anions (tetrafluoroborate, hexafluorophosphate, triflimide) were determined. The structures revealed halogen...halogen and anion...π interactions. Contacts of the type Br...Br, Br...F, Br...O, Br...N, F...F, H...Br, H...F, F...π and O...π were identified. Specific interactions were quantified by Hirshfeld surface analysis. Crystals 2012-07-27 2 3 Article 10.3390/cryst2031017 1017 1033 2073-4352 2012-07-27 doi: 10.3390/cryst2031017 Carmen Froschauer Volker Kahlenberg Gerhard Laus Herwig Schottenberger http://www.mdpi.com/2073-4352/2/3/996 A review is given for recent theoretical studies on phase transitions in quasi-one-dimensional molecular conductors with a quarter-filled band. By lowering temperature, charge transfer salts exhibit a variety of transitions accompanying symmetry breaking, such as charge ordering, lattice dimerization, antiferromagnetic transition, spin-Peierls distortion, and so on. Analyses on microscopic quasi-one-dimensional models provide their systematic understandings, by the complementary use of different analytical and numerical techniques; they can reproduce finite-temperature phase transitions, whose results can be directly compared with experiments and give feedbacks to material design. Crystals 2012-07-19 2 3 Review 10.3390/cryst2030996 996 1016 2073-4352 2012-07-19 doi: 10.3390/cryst2030996 Hideo Yoshioka Yuichi Otsuka Hitoshi Seo http://www.mdpi.com/2073-4352/2/3/984 Quasi-two-dimensional organic conductor λ-BETS2FeCl4 (BETS = bis(ethylenedithio)tetraselenafulvalene) transforms from a paramagnetic metal (PM) to an antiferromagnetic insulator (AFI) at a transition temperature, TMI, of 8.3 K under zero magnetic field. To understand the mechanism of this PM-AFI phase transition, we studied the thermodynamic properties of λ-BETS2FeCl4. We observed, below TMI, a six-level Schottky hump in its specific heat and a broad shoulder in its magnetic susceptibility. Just below the transition temperature TMI, about 80% of 3d spin degree of freedom is sustained. These temperature dependences clarify that π and 3d spins do not cooperatively form the AF order at TMI. In λ-BETS2FexGa1−xCl4 system, the increasing Fe 3d spin density enhances the internal magnetic field caused by π spin antiferromagnetic (AF) ordering, although the 3d spin itself maintains large entropy against the AF ordering. It was confirmed that the Fe 3d spin provided favorable conditions for this mysterious PM-AFI phase transition in the π electron system. We propose that this phase transition originates from the magnetic anisotropy introduced by the π-d interaction, which suppressed the low dimensional fluctuation in the π spin system. Crystals 2012-07-17 2 3 Review 10.3390/cryst2030984 984 995 2073-4352 2012-07-17 doi: 10.3390/cryst2030984 Hiroshi Akiba Kazuo Shimada Naoya Tajima Koji Kajita Yutaka Nishio http://www.mdpi.com/2073-4352/2/3/974 The crystal structures of two zincophosphate networks prepared in the presence of 1,5-diaminopentane (dap) are described. In Zn3(PO4)2(C5H14N2)2·3H2O (1) the dap forms Zn–N coordinate bonds to generate an unusual three-dimensional “hybrid” framework constructed from ZnO3N, ZnO2N2 and PO4 tetrahedra with three different types of elongated channels occupied by water molecules. In C5H16N2·Zn3(PO4)2(HPO4)·H2O; (2) the doubly-protonated H2dap acts in a more typical way to template double layers of vertex-sharing ZnO4, PO4 and HPO4 tetrahedra incorporating 10-rings and interacts with the inorganic component via N–H O hydrogen bonds. Crystal data: 1 (C10H34N4O11P2Zn3), Mr = 644.46, monoclinic, C2 (No. 4), Z = 4, a = 25.302 (7) Å, b = 4.9327 (13) Å, c = 19.808 (6) Å, b = 107.377 (8)°, V = 2359.4 (12) Å3, R(F) = 0.054, wR(F2) = 0.139. 2 (C5H19N2O13P3Zn3), Mr = 604.24, monoclinic, P21/c (No. 14), Z = 4, a = 11.3275 (15) Å, b = 8.3235 (11) Å, c = 18.588 (2) Å, b = 96.979 (3)°, V = 1739.6 (4) Å3, R(F) = 0.056, wR(F2) = 0.119. Crystals 2012-07-16 2 3 Article 10.3390/cryst2030974 974 983 2073-4352 2012-07-16 doi: 10.3390/cryst2030974 William T.A. Harrison William R. Currie http://www.mdpi.com/2073-4352/2/3/967 A facile one-pot synthesis of methyl 5-(4-chlorobenzoyloxy)-1-phenyl-1H-pyrazole-3-carboxylate (4) is described. The title compound was efficiently synthesized by the reaction of phenyl hydrazine, dimethyl acetylenedicarboxylate and 4-chlorobenzoyl chloride in dichloromethane under reflux in good yield. The structure of the target compound was deduced by modern spectroscopic and analytical techniques and unequivocally confirmed by a single crystal X-ray diffraction analysis. The crystal of the title compound belongs to orthorhombic system, space group P 21 21 21 with cell parameters a = 6.6491(3) Å, b = 7.9627(6) Å, c = 30.621(5) Å, α = β = γ = 90° and Z = 4. The crystal packing of the compound (4) is stabilized by an offset π-stacking between the planar benzoyl-substituted diazole moieties. Crystals 2012-07-16 2 3 Communication 10.3390/cryst2030967 967 973 2073-4352 2012-07-16 doi: 10.3390/cryst2030967 Imtiaz Khan Jonathan M. White http://www.mdpi.com/2073-4352/2/3/958 The crystal structure of the coordination polymer diaqua(μ-5,5'-bistetrazolato-κ4N1,N2,N5,N6)copper(II) was determined by X-ray diffraction. The copper atoms are connected to chains over the bridging 5,5'-bistetrazolato ligand. The energetic properties of the compound were investigated, such as thermal behavior and sensitivities (shock, friction, electrical spark). Crystals 2012-07-10 2 3 Article 10.3390/cryst2030958 958 966 2073-4352 2012-07-10 doi: 10.3390/cryst2030958 Manuel Joas Thomas M. Klapötke Jörg Stierstorfer http://www.mdpi.com/2073-4352/2/3/946 Electrolysis of Na and K salts of the anion dicyano(phthalocyaninato)cobalt(III) (Co(Pc)(CN)2) in ethanol yields one-dimensional partially oxidized salts of A[Co(Pc)(CN)2]2.4(EtOH) (A = Na and K). The cationic component is the supramolecular cation [A(EtOH)4]+, which forms hydrogen bonds with the CN ligands of the Co(Pc)(CN)2 units. The crystal shows metallic conductivity, in contrast to the thermally activated conductivity observed in the isomorphous tetraphenylphosphonium (TPP) salt of TPP[Co(Pc)(CN)2]2. Since the π-π interactions in these isomorphous crystals are nearly the same, the distinctive behavior of the Na and K salts may be attributed to the difference in the degree of charge disproportionation in these crystals. Crystals 2012-07-10 2 3 Article 10.3390/cryst2030946 946 957 2073-4352 2012-07-10 doi: 10.3390/cryst2030946 Yasuhiro Tanaka Manabu Ishikawa Naoko Watanabe Yukihiro Takahashi Toshio Naito Tamotsu Inabe http://www.mdpi.com/2073-4352/2/3/935 The one-pot synthesis of a Cu(II) complex with partially oxidized tetrathiafulvalene (TTF) moieties in its capping MT-Hsae-TTF ligands, [CuII(MT-sae-TTF)2] [CuICl2] was realized by the simultaneous occurrence of Cu(II) complexation and CuIICl2 mediated oxidation of TTF moieties. The crystal structure was composed of one-dimensional columns formed by partially oxidized TTF moieties and thus the cation radical salt showed relatively high electrical conductivity. Tight binding band structure calculations indicated the existence of a Peierls gap due to the tetramerization of the TTF moieties in the one-dimensional stacking column at room temperature, which is consistent with the semiconducting behavior of this salt. Crystals 2012-07-10 2 3 Article 10.3390/cryst2030935 935 945 2073-4352 2012-07-10 doi: 10.3390/cryst2030935 Hiroyuki Nishikawa Ryosuke Kitabatake Kiyotaka Mitsumoto Takuya Shiga Hiroki Oshio http://www.mdpi.com/2073-4352/2/3/893 The relationship between the conducting behavior and the degree of charge fluctuation in the β″-type BEDT-TTF salts is reviewed from the standpoints of vibrational spectroscopy and crystal structure. A group of β″-type ET salts demonstrates the best model compounds for achieving the above relationship because the two-dimensional structure is simple and great diversity in conducting behavior is realized under ambient pressure. After describing the requirement for the model compound, the methodology for analyzing the results of the vibrational spectra is presented. Vibrational spectroscopy provides the time-averaged molecular charge, the charge distribution in the two-dimensional layer, and the inter-molecular interactions, etc. The experimental results applied to 2/3-filled and 3/4-filled β″-type ET salts are reported. These experimental results suggest that the conducting property, the difference in the time-averaged molecular charges between the ionic and neutral-like sites, the alternation in the inter-molecular distances and the energy levels in the charge distributions are relevant to one another. The difference in the time-averaged molecular charges, ∆ρ, is a useful criterion for indicating conducting behavior. All superconductors presented in this review are characterized as small but finite ∆ρ. Crystals 2012-07-06 2 3 Review 10.3390/cryst2030893 893 934 2073-4352 2012-07-06 doi: 10.3390/cryst2030893 Takashi Yamamoto http://www.mdpi.com/2073-4352/2/3/875 Molecular solids are generally highly insulating. The creation of conducting molecular solids proved to be a major scientific challenge. As in the case of Si technology, the challenge started as impurity doping in band insulators and then developed into highly doped polymers, which are not crystalline. More conducting materials in crystalline forms have been realized in charge transfer (CT) complexes with two different kinds of molecules, where electrons are transferred between them in solids. In such CT complexes, not only conducting, but also even superconducting systems were achieved in 1980 and today more than 100 different superconductors are known. The most remarkable achievement in this direction was the realization of a truly metallic state in molecular solids based on a single kind of molecule. These are called single component molecular metals (SCMM) and consist of a rich variety of electronic properties. In these conducting molecular solids, CT and SCMM, many interesting electronic properties resulting from mutual Coulomb interactions and electron-phonon interactions have been explored so far, and these will be reviewed briefly in this article from a theoretical viewpoint. Challenges to come, based on these achievements, are also discussed at the end of this review. Crystals 2012-07-05 2 3 Review 10.3390/cryst2030875 875 892 2073-4352 2012-07-05 doi: 10.3390/cryst2030875 Hidetoshi Fukuyama http://www.mdpi.com/2073-4352/2/3/861 An isostructural series of anion radical salts, β'-(EtxMe4−xZ)[Pd(dmit)2]2 (x = 0–2, Z = P, As, Sb), with a quasi-triangular lattice comprising the dimer unit [Pd(dmit)2]2− belong to a strongly correlated electron system with geometrical frustration. Intra and interdimer transfer integrals between the frontier molecular orbitals, which characterize the strength of electron correlation and degree of frustration, can be tuned by selection of the counter cation. We have systematically analyzed the crystal structure with X-ray diffraction method and intermolecular transfer integrals using extended Hückel molecular orbital calculations based on structural data. The variation in the cation affects the unit cell in a manner equivalent to an anisotropic pressure. Increasing the covalent radius of the central atom Z and the number of ethyl groups (x) in the cation leads to slight arching of the Pd(dmit)2 molecule. This arch-shaped distortion of the Pd(dmit)2 molecule modifies the interdimer transfer integrals in formation of the regular triangular dimer lattice. On the other hand, the intradimer transfer integral, which is correlated with the effective on-site Coulomb interaction of the dimer, is weakly dependent on the type of cation. Crystals 2012-07-04 2 3 Article 10.3390/cryst2030861 861 874 2073-4352 2012-07-04 doi: 10.3390/cryst2030861 Reizo Kato Cui Hengbo http://www.mdpi.com/2073-4352/2/3/845 Hydrogen desorption from hydride matrix is still an open field of research. By means of accurate first-principle molecular dynamics (MD) simulations an Mg–MgH2 interface is selected, studied and characterized. Electronic structure calculations are used to determine the equilibrium properties and the behavior of the surfaces in terms of structural deformations and total energy considerations. Furthermore, extensive ab-initio molecular dynamics simulations are performed at several temperatures to characterize the desorption process at the interface. The numerical model successfully reproduces the experimental desorption temperature for the hydride. Crystals 2012-07-04 2 3 Article 10.3390/cryst2030845 845 860 2073-4352 2012-07-04 doi: 10.3390/cryst2030845 Simone Giusepponi Massimo Celino http://www.mdpi.com/2073-4352/2/3/812 Organic molecular conductors with a strongly correlated electron system, in which the itinerancy of electrons (or holes) and the electron correlation (U/W, U, the on-site Coulomb repulsion, W, the bandwidth) compete with each other, are promising candidates for achieving superconductivity and also for exploring remarkable physical properties induced by external stimuli such as pressure, light, voltage and current. Our synthetic approach to the construction of strongly correlated organic electron systems is based on chemical modifications to the donor molecule BDH-TTP [2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] capable of producing metallic CT (charge-transfer) salts stable down to low temperatures (4.2–1.5 K). This aims at enhancing the electron correlation in the itinerant electron system by decreasing the bandwidth. Chemical modifications of BDH-TTP such as ring expansion of two outer dithiolane rings, replacement of one sulfur atom in an outer dithiolane ring with an oxygen atom and introduction of two methyl substituents into an outer ditiolane ring led to BDA-TTP [2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene], DHOT-TTP [2-(1,3-dithiolan-2-ylidene)-5-(1,3-oxathiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] and DMDH-TTP [2-(4,5-dimethyl-1,3-dithiolan-2-ylidene)-5-(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene], respectively. In this review, the physical properties and the crystal and electronic structures of molecular conductors derived from these donor molecules will be described. Crystals 2012-07-04 2 3 Review 10.3390/cryst2030812 812 844 2073-4352 2012-07-04 doi: 10.3390/cryst2030812 Jun-ichi Yamada Hiroki Akutsu http://www.mdpi.com/2073-4352/2/3/762 This paper is an overview concerning the preparations and properties as well as possible applications of neutral (one component) metal 1,2-dithiolenes (and selenium analogues). The structural, chemical, electrochemical, optical and electrical behavior of these complexes depend strongly on the nature of ligand and/or the metal. The results of unsymmetrical in comparison to those of symmetrical complexes related to the properties of materials in the solid state are primarily discussed. The optical absorption spectra exhibit strong bands in the near IR spectral region ca. 700 to ca. 1950 nm. X-ray crystal structure solutions show that the complexes usually have square-planar geometry with S–S and/or M–S contacts. Some of them behave as semiconductors or conductors (metals) and are stable in air. The cyclic voltammograms at negative potentials are different from the corresponding potentials of tetrathiafulvalenes (TTFs). As a consequence, the LUMO bands occur at much lower levels than those of TTFs. Consequently, electrical measurements under conditions of field effect transistors exhibit n-type or ambipolar behavior. Illumination of materials with high power lasers exhibits non-linear optical behavior. These properties enable metal 1,2-dithiolene complexes to be classified as promising candidates for optical and electronic applications, (e.g., saturable absorbers, ambipolar inverters). Crystals 2012-06-29 2 3 Review 10.3390/cryst2030762 762 811 2073-4352 2012-06-29 doi: 10.3390/cryst2030762 George C. Papavassiliou George C. Anyfantis George A. Mousdis http://www.mdpi.com/2073-4352/2/3/741 Heat capacity measurements of κ-(BEDT-TTF)2X (BEDT-TTF: Bis(ethylendithio) tetrathiafulvalene, X: counteranions) which are classified as two-dimensional (2D) dimer-Mott system are reported. At first, we explain structural and electronic features originated from rigid dimerization in donor arrangement in 2D layers. The antiferromagnetic Mott insulating phase located at low-pressure region in the phase diagram shows vanishing γ electronic heat capacity coefficient in the heat capacity, which claims opening of a charge-gap in this insulating state. Then, a systematic change of the γ around the Mott boundary region is reported in relation to the glass freezing of ethylene dynamics. The thermodynamic parameters determined by ∆Cp/γTc of 10 K class superconductors, κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br demonstrate that a rather large gap with a strong coupling character appears around the Fermi-surface. On the other hand, the low temperature heat capacity clearly shows a picture of nodal-gap structure due to an anisotropic pairing. The comparison with lower Tc compounds in the κ-type structure is also performed so as to discuss overall features of the κ-type superconductors. The heat capacity measurements of hole-doped systems containing mercury in the counteranions show an anomalous enhancement of γ, which is consistent with the T1−1 of NMR experiments etc. The results of heat capacity measurements under high pressures are also reported. Crystals 2012-06-29 2 3 Review 10.3390/cryst2030741 741 761 2073-4352 2012-06-29 doi: 10.3390/cryst2030741 Yasuhiro Nakazawa Satoshi Yamashita http://www.mdpi.com/2073-4352/2/3/730 A gate-induced thermally stimulated current (TSC) on β′-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied VPG and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate. Crystals 2012-06-29 2 3 Article 10.3390/cryst2030730 730 740 2073-4352 2012-06-29 doi: 10.3390/cryst2030730 Masatoshi Sakai Mitsutoshi Hanada Shigekazu Kuniyoshi Hiroshi Yamauchi Masakazu Nakamura Kazuhiro Kudo http://www.mdpi.com/2073-4352/2/2/710 Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆Hdes = −78.3 kJ/molH2, ∆Sdes = −136.1 J/K molH2, estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, ∆Habs = −61.6 kJ/molH2, ∆Sabs = −110.9 J/K molH2, appear to be substantially affected by the clamping of the film to the substrate. The clamping is negligible at high temperatures, T > 523 K, while at lower temperatures, T < 393 K, it is considerable. The hysteresis at room temperature in Mg/Ta/Pd films increases by a factor of 16 as compared to MgH2 bulk. The hysteresis increases even further in Mg/Pd films, most likely due to the formation of a Mg-Pd alloy at the Mg/Pd interface. The stress–strain analysis of the Mg/Ta/Pd films at 300–333 K proves that the increase of the hysteresis occurs due to additional mechanical work during the (de-)hydrogenation cycle. With a proper temperature correction, our stress–strain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range. Crystals 2012-06-20 2 2 Article 10.3390/cryst2020710 710 729 2073-4352 2012-06-20 doi: 10.3390/cryst2020710 Yevheniy Pivak Herman Schreuders Bernard Dam http://www.mdpi.com/2073-4352/2/2/704 The new intermetallic compound Ru11Lu20 was obtained as black single crystals during an attempted comproportionation reaction of lutetium(III) chloride, LuCl3, with metallic lutetium in the presence of ruthenium metal at 950 °C. Ru11Lu20 crystallizes with the trigonal space group R-3, Z = 6, a = 1255.1(1), c = 2973.0(4) pm, R1 for all data: 0.0380. Ruthenium atoms center eight-, nine- and ten-vertex polyhedra of lutetium atoms which are connected in a complicated manner to a three-dimensional network. Crystals 2012-06-20 2 2 Article 10.3390/cryst2020704 704 709 2073-4352 2012-06-20 doi: 10.3390/cryst2020704 Sina Zimmermann Ingo Pantenburg Gerd Meyer http://www.mdpi.com/2073-4352/2/2/690 In spite of their favourable chemical characteristics, using AB5 alloys as fixed bed for hydrogen storage devices requires proper management of a number of technological aspects. Among these, the mechanical stability of metal particle grains under hydrogen cycling and the overall thermal conductivity of the material bed constitute crucial features. We developed by High Energy Ball Milling HEBM a mechanically stable silica-based AB5 composite with enhanced thermal conductivity. Here, focusing on the material’s physical-chemical properties, we report on the silica-AB5 composite development and characterization. Particularly, we studied the material consolidation process, the resulting composite morphology and the system behaviour under hydrogen loading/unloading cycling. Crystals 2012-06-18 2 2 Article 10.3390/cryst2020690 690 703 2073-4352 2012-06-18 doi: 10.3390/cryst2020690 Marzia Pentimalli Enrico Imperi Mariangela Bellusci Carlo Alvani Andrea Santini Franco Padella http://www.mdpi.com/2073-4352/2/2/675 1-Amino-3-nitroguanidine (ANQ, 1) was synthesized by hydrazinolysis of nitroguanidine (NQ) with hydrazine hydrate. Four different amino-nitroguanidinium salts (chloride (2), bromide (3), iodide (4) and sulfate (5)) were synthesized and structurally characterized by low-temperature X-ray diffraction. The halides 2–4 could only be obtained crystalline as monohydrates. In addition, they were characterized by NMR and vibrational spectroscopy, elemental analysis and the sensitivities towards impact, friction and electrostatic discharge were determined. The compounds can be used in silver (AgX, X = Cl, Br, I) and barium (BaSO4) based metathesis reactions in order to form more complex salts of 1-amino-nitroguanidine. Crystals 2012-06-18 2 2 Article 10.3390/cryst2020675 675 689 2073-4352 2012-06-18 doi: 10.3390/cryst2020675 Niko Fischer Thomas M. Klapötke Karin Lux Franz A. Martin Jörg Stierstorfer http://www.mdpi.com/2073-4352/2/2/669 Methyl 4-hydroxy-3-nitrobenzoate, (I), C8H7NO5, crystallizes with two unique molecules, A and B, in the asymmetric unit of the triclinic unit cell. The space group was assigned as P-1, with lattice parameters a = 0.72831(15), b = 1.0522(2), c = 1.1410(2) nm, α = 83.38(3), β = 80.83(3), γ = 82.02(3)°, Z = 4, V = 0.8510(3) nm3, Mr = 197.15, Dc = 1.539 g/m3, µ= 0.131 mm−1, F(000) = 408, R = 0.1002 and wR = 0.2519. In the crystal structure, 12 hydrogen bonding and two p-stacking interactions link the molecules into infinite stacked sheets parallel to (101). Crystals 2012-06-12 2 2 Communication 10.3390/cryst2020669 669 674 2073-4352 2012-06-12 doi: 10.3390/cryst2020669 Xin-Ling Fu Jiang-Sheng Li Jim Simpson http://www.mdpi.com/2073-4352/2/2/662 Three TCNQ derivatives carrying nitroxide radicals (3a–3c) were prepared and were found to form single-component charge-transfer (CT) complexes by self-assembly, in which outer nitroxide groups of a couple of different molecules work as donors and the inner TCNQ unit of another molecule as an acceptor. While the CT interactions found for the TEMPO (2,2,6,6-tetramethylpiperidin-1-oxy) derivative 3a and the PROXYL (2,2,5,5-tetramethylpirrolidin-1-oxy) derivative 3b are point-to-face fashion between the oxygen atom of each nitroxide group and the six-membered ring of inner TCNQ unit, the CT interactions found for the PO (2,2,5,5-tetramethyl-3-pyrrolin-1-oxy) derivative 3c are point-to-point contacts between the oxygen atoms of outer nitroxide groups and the carbon atoms of a couple of cyano groups. Crystals 2012-06-12 2 2 Article 10.3390/cryst2020662 662 668 2073-4352 2012-06-12 doi: 10.3390/cryst2020662 Hideto Suzuki Hiroki Akutsu Jun-ichi Yamada Shin’ichi Nakatsuji http://www.mdpi.com/2073-4352/2/2/643 A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermion system with anisotropic Fermi velocity. This system exhibits remarkable transport phenomena characteristic to electrons on the Dirac cone type energy structure. Crystals 2012-06-11 2 2 Review 10.3390/cryst2020643 643 661 2073-4352 2012-06-11 doi: 10.3390/cryst2020643 Naoya Tajima Yutaka Nishio Koji Kajita http://www.mdpi.com/2073-4352/2/2/627 We report on the single-crystal-to-single-crystal transformation occurring over time in a layered organic molecular conductor based on BEDT-TTF. The process is connected with removal of solvent molecules from the complex anion layer resulting in concomitant partial irreversible conversion of the δ-(BEDT-TTF)4[OsNOCl5]1.33(C6H5NO2)0.67 structure to the β"-(BEDT-TTF)3[OsNOCl5] structure. Along with symmetry lowering from I2/a to Р, huge, drastic changes in the conducting BEDT-TTF layer as well as in the anion arrangement are observed, meanwhile crystallinity of the sample is retained. Coexistence of two phases, parent δ and daughter β" in the same crystal helps in the study of their mutual orientation as well as to formulate a mechanism for the structural transformation. Crystals 2012-06-07 2 2 Article 10.3390/cryst2020627 627 642 2073-4352 2012-06-07 doi: 10.3390/cryst2020627 Leokadiya Zorina Sergey Simonov Enric Canadell Rimma Shibaeva http://www.mdpi.com/2073-4352/2/2/618 CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared using water-in-heptane or water-in-nonane microemulsions. The results obtained from the investigation of nanocrystals prepared using heptane as the organic phase, confirmed that nanocrystal nucleation is fast while their growth is determined by droplet exchange content rate. Size distribution histograms obtained from the sample at early time points after mixing presented a bimodal population having average sizes of 3.0 ± 0.1 and 5.8 ± 0.1 nm, thus indicating that surface process controls the nanocrystal growth. With longer reaction times the occurrence of water droplet coalescence is likely responsible for the formation of nanocrystal agglomerates. Using a water-in-nonane microemulsion, the droplet exchange rate can be modified, thus leading to smaller CdS nanocrystals. However, the development of structural defects cannot be excluded, as evidenced by the luminescence spectra of the suspension. In general, aging of the nanocrystal in the pristine microemulsion resulted in the development of cubic semiconductor nanostructures. Crystals 2012-06-06 2 2 Article 10.3390/cryst2020618 618 626 2073-4352 2012-06-06 doi: 10.3390/cryst2020618 Loredana Latterini Alessandro Iagatti http://www.mdpi.com/2073-4352/2/2/590 Photoinduced phase transitions in organic compounds with strong electron correlation ET [bis(ethylenedithio)-tetrathiafulvalene)-based salts α-(ET)2I3, θ-(ET)2RbZn(SCN)4, κ-(d-ET)2Cu[N(CN)2Br] were discussed based, on time resolved optical pump-probe spectroscopy using ~150 fs mid-infrared pulse, 12 fs near infrared pulse, and sub-picosecond terahertz pulse. (i) In charge-ordered insulators α-(ET)2I3 and θ-(ET)2RbZn(SCN)4, we captured ultrafast snapshots of charge dynamics i.e., immediate (ca. 15 fs) generation of a microscopic metallic state (or equivalently the microscopic melting of the charge order) which is driven by the coherent oscillation (period; 18 fs) of correlated electrons. Subsequently, condensation of the microscopic metallic state to the macroscopic scale occurs in α-(ET)2I3. However, in θ-(ET)2RbZn(SCN)4, such condensation is prevented by the large potential barrier reflecting the structural difference between the insulator and metal; (ii) In a Dimer–Mott insulator κ-(d-ET)2Cu[N(CN)2Br], photogeneration of the metallic state rises during ca. 1 ps that is much slower than the melting of charge order, because the photoinduced insulator to metal transition is driven by the intradimer molecular displacement in the dimer Mott insulator. The ultrafast dynamics of photoinduced insulator–metal transitions depend strongly on the molecular arrangement, reflecting various competing phases in the ET sheets. Crystals 2012-05-30 2 2 Review 10.3390/cryst2020590 590 617 2073-4352 2012-05-30 doi: 10.3390/cryst2020590 Shinichiro Iwai http://www.mdpi.com/2073-4352/2/2/579 The interplane spin cross relaxation time Tx measured by high frequency ESR in X-ray irradiated κ-(BEDT-TTF)2Cu[N(CN)2]Cl is compared to the interplane resisitivity ρ⊥and the in-plane resistivity ρII between 50 K and 250 K. The irradiation transforms the semiconductor behavior of the non-irradiated crystal into metallic. Irradiation decreases Tx, ρ⊥ and ρII but the ratio Tx/ρ⊥ and ρ⊥/ρII remain unchanged between 50 and 250 K. Models describing the unusual defect concentration dependence in κ-(BEDT-TTF)2Cu[N(CN)2]Cl are discussed. Crystals 2012-05-24 2 2 Article 10.3390/cryst2020579 579 589 2073-4352 2012-05-24 doi: 10.3390/cryst2020579 Ágnes Antal Titusz Fehér Naoki Yoneyama László Forró Takahiko Sasaki András Jánossy http://www.mdpi.com/2073-4352/2/2/528 Charge ordering in the (TMTTF)2X salts with centrosymmetric anions (X = PF‾6 , AsF‾6 , SbF‾6 ) leads to a ferroelectric state around 100 K. For the first time and in great completeness, the intra- and intermolecular vibrational modes of (TMTTF)2X have been investigated by infrared and Raman spectroscopy as a function of temperature and pressure for different polarizations. In this original paper, we explore the development and amount of charge disproportionation and the coupling of the electronic degrees of freedom to the counterions and the underlying lattice. The methyl groups undergo changes with temperature that are crucial for the anion cage formed by them. We find that the coupling of the TMTTF molecules to the hexafluorine anions changes upon cooling and especially at the charge-order transition, indicating a distortion of the anion. Additional features are identified that are caused by the anharmonic potential. The spin-Peierls transition entails additional modifications in the charge distribution. To complete the discussion, we also add the vibrational frequencies and eigenvectors based on ab-initio quantum-chemical calculations. Crystals 2012-05-23 2 2 Article 10.3390/cryst2020528 528 578 2073-4352 2012-05-23 doi: 10.3390/cryst2020528 Martin Dressel Michael Dumm Tobias Knoblauch Matteo Masino http://www.mdpi.com/2073-4352/2/2/521 The acid catalyzed esterification of 2,6-dimethoxybenzoic acid (1) in the presence of absolute ethanol afforded ethyl 2, 6-dimethoxybenzoate (2). The structure of the resulting compound was supported by spectroscopic data and unambiguously confirmed by single crystal X-ray diffraction studies. The title compound crystallized in the triclinic space group P ī with unit cell parameters a = 8.5518(3) Å, b = 10.8826(8) Å, c = 11.9939(6) Å, α = 101.273(5)°, β = 98.287(3)°, γ = 94.092(4)°, V = 1077.54(10) Å3, Z = 4, Dc = 1.296 Mg/m3, F(000) = 448 and μ = 0.098 mm−1. Compound (2) crystallizes with two molecules in the asymmetric unit with similar conformations. Crystals 2012-05-22 2 2 Communication 10.3390/cryst2020521 521 527 2073-4352 2012-05-22 doi: 10.3390/cryst2020521 Imtiaz Khan Aliya Ibrar Jonathan M. White http://www.mdpi.com/2073-4352/2/2/466 We review structural aspects of the Bechgaard and Fabre salts in relationship with their electronic, magnetic and superconducting properties. We emphasize the role of bond and charge modulations of the quarter filled organic stack in the various instabilities and ground states exhibited by these salts. A special consideration is also devoted to the influence of anions and methyl groups in these processes. In particular we point out the importance of the anions in achieving the inter-stack coupling by either direct or indirect (via the polarization of the methyl group cavities) interactions with the donors. In this framework we discuss the role of anions and methyl group disorders in the inhibition of the divergence of the high temperature bond order wave instability of the Bechgaard salts. We analyze the modulation in the magnetic ground states by considering explicitly the coupling of the magnetization with structural degrees of freedom. We consider the role of the anions and methyl groups in stabilizing the charge ordering pattern in the Fabre salts. We also discuss the spin-Peierls transition of the Fabre salts in relation with the charge ordering transition and the adiabaticity of the phonon field. We review the anion ordering transitions by considering more particularly the influence of the ordering process on the electronic structure and on the ground states which results. In this framework we show that the texture of the anion ordered structure has direct consequences on the superconducting properties of (TMTSF)2ClO4. Finally we conclude on the essential implication of the structural degrees of freedom on the generic phase diagram of the Bechgaard and Fabre salts. Crystals 2012-05-21 2 2 Review 10.3390/cryst2020466 466 520 2073-4352 2012-05-21 doi: 10.3390/cryst2020466 Jean-Paul Pouget http://www.mdpi.com/2073-4352/2/2/446 We report the preparation, crystallization and solid state characterization of a cyclohexanemethylamine substituted spirobiphenalenyl radical; in the solid state the compound is iso-structural with its dehydro-analog (benzylamine-substitued compound), and the molecules packed in a one-dimensional fashion that we refer to as a π-step stack. Neighboring molecules in the stack interact via the overlap of one pair of active (spin bearing) carbon atoms per phenalenyl unit. The magnetic susceptibility measurement indicates that in the solid state the radical remains paramagnetic and the fraction of Curie spins is 0.75 per molecule. We use the analytical form of the Bonner-Fisher model for the S = 1/2 antiferromagnetic Heisenberg chain of isotropically interacting spins with intrachain spin coupling constant J = 6.3 cm−1, to fit the experimentally observed paramagnetism [χp (T)] in the temperature range 4–330 K. The measured room temperature conductivity (σRT = 2.4 × 10–3 S/cm) is comparable with that of the iso-structural benzyl radical, even though the calculated band dispersions are smaller than that of the unsaturated analog. Crystals 2012-05-14 2 2 Article 10.3390/cryst2020446 446 465 2073-4352 2012-05-14 doi: 10.3390/cryst2020446 Pradip Bag Mikhail E. Itkis Sushanta K. Pal Elena Bekyarova Bruno Donnadieu Robert C. Haddon http://www.mdpi.com/2073-4352/2/2/413 Hydrogen has many positive attributes that make it a viable choice to augment the current portfolio of combustion-based fuels, especially when considering reducing pollution and greenhouse gas (GHG) emissions. However, conventional methods of storing H2 via high-pressure or liquid H2 do not provide long-term economic solutions for many applications, especially emerging applications such as man-portable or stationary power. Hydrogen storage in materials has the potential to meet the performance and cost demands, however, further developments are needed to address the thermodynamics and kinetics of H2 uptake and release. Therefore, the US Department of Energy (DOE) initiated three Centers of Excellence focused on developing H2 storage materials that could meet the stringent performance requirements for on-board vehicular applications. In this review, we have summarized the developments that occurred as a result of the efforts of the Metal Hydride and Chemical Hydrogen Storage Centers of Excellence on materials that bind hydrogen through ionic and covalent linkages and thus could provide moderate temperature, dense phase H2 storage options for a wide range of emerging Proton Exchange Membrane Fuel Cell (PEM FC) applications. Crystals 2012-05-10 2 2 Review 10.3390/cryst2020413 413 445 2073-4352 2012-05-10 doi: 10.3390/cryst2020413 Scott McWhorter Kathleen O’Malley Jesse Adams Grace Ordaz Katie Randolph Ned T. Stetson http://www.mdpi.com/2073-4352/2/2/393 Tetrathiafulvalene derivatives condensed with 2-alkylidene-1,3-dithiole moiety, MeDTES (2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), EtDTES (2-(pentan-3-ylidene)-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), and CPDTES (2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene) have been synthesized. Crystal structure analysis of MeDTES salts with Au(CN)4−, ReO4−, and I3− and a CPDTES salt with I3− reveals that the donor−anion ratios of all salts are 1:1. Band calculation of (MeDTES)[Au(CN)4] suggests a quasi-one-dimensional Fermi surface that could be the result of the uniform stack of donor molecules. In spite of this stacking, the salt is a Mott insulator because of a large on-site Coulomb interaction U. (MeDTES)(ReO4)(H2O)0.5 possesses Fermi points and exhibits semiconducting behavior with small activation energy (Ea = 0.058 eV). I3− ions form disordered infinite chain in (MeDTES)(I3)(DCE)0.25, but those in (CPDTES)(I3) exist as discrete ions. They show low conductivity (10−4−10−2 S cm−1) at room temperature and the band calculation suggests that they are band insulator. Crystals 2012-05-09 2 2 Article 10.3390/cryst2020393 393 412 2073-4352 2012-05-09 doi: 10.3390/cryst2020393 Keisuke Furuta Shuhei Kohno Takashi Shirahata Koya Yamasaki Shojun Hino Yohji Misaki http://www.mdpi.com/2073-4352/2/2/374 The Mott-Anderson transition has been known as a metal-insulator (MI) transition due to both strong electron-electron interaction and randomness of the electrons. For example, the MI transition in doped semiconductors and transition metal oxides has been investigated up to now as a typical example of the Mott-Anderson transition for changing electron correlations by carrier number control in concurrence with inevitable randomness. On the other hand, molecular conductors have been known as typical strongly correlated electron systems with bandwidth controlled Mott transition. In this paper, we demonstrate our recent studies on the randomness effect of the strongly correlated electrons of the BEDT-TTF molecule based organic conductors. X-ray irradiation on the crystals introduces molecular defects in the insulating anion layer, which cause random potential modulation of the correlated electrons in the conductive BEDT-TTF layer. In combination with hydrostatic pressure, we are able to control the parameters for randomness and correlations for electrons approaching the Mott-Anderson transition. Crystals 2012-05-08 2 2 Review 10.3390/cryst2020374 374 392 2073-4352 2012-05-08 doi: 10.3390/cryst2020374 Takahiko Sasaki http://www.mdpi.com/2073-4352/2/2/362 A polyoxotungstate-surfactant hybrid layered compound was synthesized as a single phase by using decatungstate ([W10O32]4−, W10) and hexadecylpyridinium (C16py). The X-ray structure analysis combined with infrared spectroscopy and elemental analysis revealed the formula to be (C16py)4[W10O32] (C16py-W10). The layered structure consisted of alternative stacking of W10 inorganic monolayers and interdigitated C16py bilayers with layered periodicity of 23.3 Å. Each W10 anion in the W10 inorganic monolayers was isolated by the hydrophilic heads of C16py. The hybrid crystals of C16py-W10 decomposed at around 500 K. The conductivity of the hybrid layered crystal was estimated to be 4.8 × 10−6 S cm−1 at 423 K by alternating current (AC) impedance spectroscopy. Crystals 2012-05-03 2 2 Article 10.3390/cryst2020362 362 373 2073-4352 2012-05-03 doi: 10.3390/cryst2020362 Takeru Ito Nozomu Fujimoto Sayaka Uchida Jun Iijima Haruo Naruke Noritaka Mizuno http://www.mdpi.com/2073-4352/2/2/349 Three N-substituted 5-chlorosalicylamides (4-chlorophenyl, 2a; benzyl, 2b; phenethyl 2c) differing in the length of the 'linker' between the benzene ring and the amide moiety were prepared in order to compare their supramolecular architecture. The intramolecular NH···O(H) hydrogen bond and the intermolecular C=O···H–O hydrogen bond were found in the crystal structure of 2a and 2c thus forming an infinite linear chain. Compound 2b had a different arrangement with the intramolecular C=O···H–O hydrogen bond and another intermolecular NH···O(H) hydrogen forming a linear infinite chain. Crystals 2012-05-03 2 2 Article 10.3390/cryst2020349 349 361 2073-4352 2012-05-03 doi: 10.3390/cryst2020349 Aleš Imramovský Karel Pauk Zdeňka Padělková Jiří Hanusek http://www.mdpi.com/2073-4352/2/2/338 The condensation reaction of (4-(6,7-dimethyldithio-tetrathiafulvalene)-aniline) with 2,6-diformylpyridine afforded an electroactive Schiff base (N,N,N) pincer (3). This pincer was reacted with Zn(II) cation to yield the corresponding Zinc chloride complex (4). The crystal structure of the newly prepared electroactive zinc complex reveals that the tetrathiafulvalene (TTF) is neutral and the zinc cation is pentacoordinated. The two chlorines are involved in a set of hydrogen bonds giving rise to a 2D supramolecular grid arrangement. The electronic absorption properties and the electrochemical behavior have been elucidated. These two compounds are promising for the construction of crystalline radical cation salts. Crystals 2012-04-24 2 2 Article 10.3390/cryst2020338 338 348 2073-4352 2012-04-24 doi: 10.3390/cryst2020338 Gabriela Nita Diana Branzea Flavia Pop Abdelkrim El-Ghayoury Narcis Avarvari http://www.mdpi.com/2073-4352/2/2/327 Oxidation of 3,4-ethylenedithio-3'-iodo-tetrathiafulvalene (EDT-TTF-I) and 3,4-ethylenedithio-3',4'-diiodo-tetrathiafulvalene (EDT-TTF-I2) with DDQ afforded two different salts formulated as (EDT-TTF-I)(DDQ) and (EDT-TTF-I2)2(DDQ)·(CH3CN), both characterized with a full charge transfer to the DDQ acceptor moiety and by short and linear halogen bonding interactions between the iodine atom as halogen bond donor, and the carbonyl oxygen or the nitrile nitrogen atoms of reduced DDQ. Crystals 2012-04-24 2 2 Article 10.3390/cryst2020327 327 337 2073-4352 2012-04-24 doi: 10.3390/cryst2020327 Julien Lieffrig Olivier Jeannin Kyoung-Soon Shin Pascale Auban-Senzier Marc Fourmigué http://www.mdpi.com/2073-4352/2/2/306 Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN)2]32−), two closely related radical salts: α'-(ET)4tcpd·THF (1) (THF = tetrahydrofurane) and α'-(ET)4tcpd·H2O (2) have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH− (=[(NC)2CC(OCH2CH2OH)C(CN)2]−) two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET)2(tcnoetOH) (3) and β''-(ET)2(tcnoetOH) (4). Finally, with the mono-anion tcnoprOH− (=[(NC)2CC(OCH2CH2CH2OH)C(CN)2]−) we have prepared a metallic radical salt: β''-(ET)2(tcnoprOH)(CH2Cl2CH3Cl)0.5 (5). Salts 1‑4 are semiconductors with high room temperature conductivities and activation energies in the range 0.1–0.5 eV, whereas salt 5 is metallic down to 0.4 K although it does not show any superconducting transition above this temperature. Crystals 2012-04-23 2 2 Article 10.3390/cryst2020306 306 326 2073-4352 2012-04-23 doi: 10.3390/cryst2020306 Samia Benmansour Mathieu Marchivie Smail Triki Carlos J. Gómez-García http://www.mdpi.com/2073-4352/2/2/294 5-Azido-3-nitro-1H-1,2,4-triazole, its methyl derivative and potassium salt were synthesized and characterized by various spectroscopic methods. The crystal structures were determined by low temperature single crystal X-ray diffraction. The interactions between the molecules or ions were analyzed and discussed. Furthermore, all compounds were tested according to BAM (Bundesanstalt für Materialforschung und -prüfung) methods. Crystals 2012-04-23 2 2 Article 10.3390/cryst2020294 294 305 2073-4352 2012-04-23 doi: 10.3390/cryst2020294 Dániel Izsák Thomas M. Klapötke http://www.mdpi.com/2073-4352/2/2/284 A new mixed-anion crystal composed of BEDT-TTF radical cation salt [BEDT-TTF]2(CuBr2)0.4(CuCl2)0.6 with an α'-type donor arrangement with a formal charge of +0.5 per BEDT-TTF was prepared by using a chemical oxidation method and characterized by using X-ray diffraction, four-probe electrical resistivity measurements (semiconductor: ρrt = 2 × 102 Ω cm, Ea = 0.2 eV), and energy band calculations. The results showed that this system had a quasi-one dimensional Fermi surface. Crystals 2012-04-23 2 2 Article 10.3390/cryst2020284 284 293 2073-4352 2012-04-23 doi: 10.3390/cryst2020284 Kazuya Kubo Masahiro Yamashita http://www.mdpi.com/2073-4352/2/2/266 The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon for the intermediate magnitude of momentum owing to the combined effects of two tilted cones. Dirac electrons with the zero-gap state (ZGS) in organic conductor α-(BEDT-TTF)2I3 are examined by calculating the Berry curvature, which displays the peak structure for a pair of Dirac particles between the conduction band and the valence band. The ZGS is theoretically predicted for α-(BEDT-TTF)2NH4Hg(SCN)4 under uniaxial pressure. Examining the band structure of the stripe charge ordered state of α-(BEDT-TTF)2I3 under pressure, we have found a topological transition from a conventional insulator to a new phase of a pair of Dirac electrons with a finite mass. Further, investigating the zero-energy (N = 0) Landau level under a strong magnetic field, we propose ferromagnetism breaking the SU(2) valley-pseudo-spin symmetry, and the phase fluctuations of the order parameters leading to Kosterlitz-Thouless transition at lower temperatures. Crystals 2012-04-20 2 2 Review 10.3390/cryst2020266 266 283 2073-4352 2012-04-20 doi: 10.3390/cryst2020266 Yoshikazu Suzumura Akito Kobayashi http://www.mdpi.com/2073-4352/2/2/248 In this short review, I will give an overview on the current understanding of the superconductivity in quasi-two-dimensional organic metals. Thereby, I will focus on charge-transfer salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET for short). In these materials, strong electronic correlations are clearly evident, resulting in unique phase diagrams. The layered crystallographic structure leads to highly anisotropic electronic as well as superconducting properties. The corresponding very high orbital critical field for in-plane magnetic-field alignment allows for the occurrence of the Fulde–Ferrell– Larkin–Ovchinnikov state as evidenced by thermodynamic measurements. The experimental picture on the nature of the superconducting state is still controversial with evidence both for unconventional as well as for BCS-like superconductivity. Crystals 2012-04-19 2 2 Review 10.3390/cryst2020248 248 265 2073-4352 2012-04-19 doi: 10.3390/cryst2020248 Jochen Wosnitza http://www.mdpi.com/2073-4352/2/2/236 Calculating electron-vibration (vibronic) interaction constants is computationally expensive. For molecules containing N nuclei it involves solving the Schrödinger equation for Ο(3N) nuclear configurations in addition to the cost of determining the vibrational modes. We show that quantum vibronic interactions are proportional to the classical atomic forces induced when the total charge of the system is varied. This enables the calculation of vibronic interaction constants from O(1) solutions of the Schrödinger equation. We demonstrate that the O(1) approach produces numerically accurate results by calculating the vibronic interaction constants for several molecules. We investigate the role of molecular vibrations in the Mott transition in κ-(BEDT-TTF)2Cu[N(CN)2]Br. Crystals 2012-04-18 2 2 Article 10.3390/cryst2020236 236 247 2073-4352 2012-04-18 doi: 10.3390/cryst2020236 Benjamin J. Powell Tunna Baruah Mark R. Pederson