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Crystals, Volume 8, Issue 4 (April 2018)

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Cover Story (view full-size image) One of the main concepts of structural design for low-dimensional magnetic systems is the [...] Read more.
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Open AccessArticle β”-(CNB-EDT-TTF)4BF4; Anion Disorder Effects in Bilayer Molecular Metals
Crystals 2018, 8(4), 142; doi:10.3390/cryst8040142
Received: 3 March 2018 / Revised: 17 March 2018 / Accepted: 18 March 2018 / Published: 21 March 2018
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Abstract
The preparation and characterization of new salts based on the dissymmetrical TTF derivative CNB-EDT-TTF (cyanobenzene-ethylenedithio-tetrathiafulvalene) and BF4 anions, are reported. Depending on the electrocrystallization conditions salts with different stoichiometries, (CNB-EDT-TTF)BF4 and β”-(CNB-EDT-TTF)4BF4, can be obtained.
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The preparation and characterization of new salts based on the dissymmetrical TTF derivative CNB-EDT-TTF (cyanobenzene-ethylenedithio-tetrathiafulvalene) and BF4 anions, are reported. Depending on the electrocrystallization conditions salts with different stoichiometries, (CNB-EDT-TTF)BF4 and β”-(CNB-EDT-TTF)4BF4, can be obtained. The 1:1 salt is an electrical insulator isostructural to the ClO4 analogue previously described. The 4:1 salt is a new member of the family of 2D metals of this donor with different small anions X, (CNB-EDT-TTF)4X, characterized by a bilayer arrangement of the donors and it was obtained in a monoclinic polymorph with a β”-type donor packing pattern. The small anions in this compound are severely disordered between the donor bilayers, which present slightly larger lattice parameters than the isostructural ClO4 analogue. Both electrical conductivity and thermoelectric power measurements in single crystals denote metallic properties as predicted by electronic band structure calculations. As a consequence of the anion disorder the metallic regime of the electrical conductivity denotes electronic localization effects with a progressive increase of resistivity below ~25 K. Because of the larger lattice parameters the intermolecular interactions and electronic bandwidth are decreased compared to other (CNB-EDT-TTF)4X salts. The large and positive thermoelectric power S of this compound (~110 μV/K in the range 100–330 K) and its electrical conductivity σ = 20 S/cm at room temperature lead to a power factor S2σ = 24 μW/K2m, quite large among molecular conductors, placing these compounds as potential candidates for thermoelectric materials. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessCommunication Unprecedented Hexanuclear Cobalt(II) Nonsymmetrical Salamo-Based Coordination Compound: Synthesis, Crystal Structure, and Photophysical Properties
Crystals 2018, 8(4), 144; doi:10.3390/cryst8040144
Received: 26 February 2018 / Revised: 16 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
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Abstract
A novel hexanuclear Co(II) coordination compound with a nonsymmetrical Salamo-type bisoxime ligandH4L, namely [{Co3(HL)(MeO)(MeOH)2(OAc)2}2]·2MeOH, was prepared and characterized by elemental analyses, UV–vis, IR and fluorescence spectra, and X-ray single-crystal diffraction analysis. Each Co(II)
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A novel hexanuclear Co(II) coordination compound with a nonsymmetrical Salamo-type bisoxime ligandH4L, namely [{Co3(HL)(MeO)(MeOH)2(OAc)2}2]·2MeOH, was prepared and characterized by elemental analyses, UV–vis, IR and fluorescence spectra, and X-ray single-crystal diffraction analysis. Each Co(II) is hexacoordinated, and possesses a distorted CoO6 or CoO4N2 octahedrons. The Co(II) coordination compound possesses a self-assembled infinite 2D supramolecular structure with the help of the intermolecular C–H···O interactions. Meanwhile, the photophysical properties of the Co(II) coordination compound were studied. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Ageing and Langmuir Behavior of the Cage Occupancy in the Nitrogen Gas Hydrate
Crystals 2018, 8(4), 145; doi:10.3390/cryst8040145
Received: 22 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 23 March 2018
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Abstract
Clathrate hydrates are ice-like systems in which nanometric water cages encapsulate guest molecules. Functionalizing clathrate hydrates is an important issue, accomplished by playing with their chemical composition and their cage structure. In this issue, the cage occupancy and its kinetics constitute key information
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Clathrate hydrates are ice-like systems in which nanometric water cages encapsulate guest molecules. Functionalizing clathrate hydrates is an important issue, accomplished by playing with their chemical composition and their cage structure. In this issue, the cage occupancy and its kinetics constitute key information for future developments. In many aspects, nitrogen gas hydrate represents an interesting system not only for its applied relevance (e.g., gas separation and methane/carbon dioxide exchange), but also for its fundamental interest (e.g., structural metastability and kinetics). Thanks to the complementarity of neutron diffraction and Raman scattering, the vibrational signatures of the so-called SI and SII clathrate structures of the nitrogen hydrates are reviewed. Moreover, the investigation of the ageing of the SII structure is reported together with its interpretation in the frame of the Langmuir behavior of the cage filling at low temperature. The cage filling is monitored with the help of a time-dependent analysis of the Raman scattering signals (over several months). The SII large cage filling decreases with a kinetic rate of 5.9 ± 3.3 × 10 3 h−1 at 77 K and atmospheric pressure, so that equilibrium is reached after ca. eight weeks. Isotherm measurements of the guest Raman signatures lead to revealing a Langmuir constant higher in the small cage than in the large cage at 150 K. Such a behavior might thus be correlated with the nitrogen depletion with time, observed in the large cage of the SII nitrogen hydrate. Full article
(This article belongs to the Special Issue Functional Multi-Scale Crystals)
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Open AccessArticle Design and Crystal Structures of Two New Compounds Fused with 3,4,5-Trimethoxybenzyl Group and 6,10-Dioxaspiro Group
Crystals 2018, 8(4), 146; doi:10.3390/cryst8040146
Received: 7 March 2018 / Revised: 14 March 2018 / Accepted: 15 March 2018 / Published: 23 March 2018
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Abstract
Two new compounds, 8-(3,4,5-trimethoxybenzylidene)-6,10-dioxaspiro[4,5]decane-7,9-dione (J1) and 8-(3,4,5-trimethoxybenzyl)-6,10-dioxaspiro[4,5]decane-7,9-dione (J2) have been designed and generated by the reaction of 3,4,5-trimethoxybenzaldehyde with 6,10-dioxaspiro[4,5]decane-7,9-dione in different solvents. The 3,4,5-trimethoxybenzyl group of the two compounds connects with the dioxaspiro group via double bond (
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Two new compounds, 8-(3,4,5-trimethoxybenzylidene)-6,10-dioxaspiro[4,5]decane-7,9-dione (J1) and 8-(3,4,5-trimethoxybenzyl)-6,10-dioxaspiro[4,5]decane-7,9-dione (J2) have been designed and generated by the reaction of 3,4,5-trimethoxybenzaldehyde with 6,10-dioxaspiro[4,5]decane-7,9-dione in different solvents. The 3,4,5-trimethoxybenzyl group of the two compounds connects with the dioxaspiro group via double bond (J1) and single bond (J2), respectively. The crystal structure determinations show that Compound J1 belongs to the triclinic system, space group P-1 with a = 5.4056(11) Å, b = 11.465(2) Å, c = 13.502(3) Å, α = 92.06(3)° Å, β = 91.35(3)°, γ = 93.50(3)°, C18H20O7, Mr = 348.34, V = 834.4(3) Å3, Z = 2, Dc = 1.386 g/cm3, F(000) = 368. Compound J2 is also of the triclinic system, space group P-1 with a = 8.8778(18) Å, b = 9.5285(19) Å, c = 11.082(4) Å, α = 89.69(3)°, β = 67.38(3)°, γ = 81.68(3)°, C18H22O7, Mr = 250.36, V = 854.9(3) Å3, Z = 2, Dc = 1.361 g/cm3, F(000) = 372. Both compounds form three-dimensional network structures via C–H···O intra- and intermolecular hydrogen bonds. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Synthesis and Characterization of Photo-Responsive Thermotropic Liquid Crystals Based on Azobenzene
Crystals 2018, 8(4), 147; doi:10.3390/cryst8040147
Received: 24 February 2018 / Revised: 21 March 2018 / Accepted: 22 March 2018 / Published: 26 March 2018
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Abstract
A series of new thermotropic liquid crystals (LCs) containing azobenzene units was synthesized. The structures of the compounds were characterized by means of NMR and FTIR spectroscopy. Their mesomorphic behaviors were investigated via differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Based
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A series of new thermotropic liquid crystals (LCs) containing azobenzene units was synthesized. The structures of the compounds were characterized by means of NMR and FTIR spectroscopy. Their mesomorphic behaviors were investigated via differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Based on the POM and DSC measurements, the optical properties of the Razo-ester were tested using UV-vis spectroscopy. The azobenzene side chain displayed a strong ability to influence the formation of thermotropic LCs. Full article
(This article belongs to the Section Liquid Crystals)
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Open AccessArticle Exciton Spectroscopy of Spatially Separated Electrons and Holes in the Dielectric Quantum Dots
Crystals 2018, 8(4), 148; doi:10.3390/cryst8040148
Received: 26 February 2018 / Revised: 23 March 2018 / Accepted: 25 March 2018 / Published: 27 March 2018
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Abstract
It is shown that in the potential energy of an exciton of spatially separated electrons and holes (hole moves in the amount of quantum dots (QDs), and the electron is localized on a spherical surface section (QD—dielectric matrix)) taking into account centrifugal energy
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It is shown that in the potential energy of an exciton of spatially separated electrons and holes (hole moves in the amount of quantum dots (QDs), and the electron is localized on a spherical surface section (QD—dielectric matrix)) taking into account centrifugal energy gives rise band of the quasi-stationary surface exciton states that with the increase of the radius of QD becomes stationary state. The mechanisms of formation of the spectra of interband and intraband absorption (emission) of light in nanosystems containing aluminum oxide QDs, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the area of the surface exciton states cause significant absorption in the visible and near infrared wavelengths, and cause the experimentally observed significant blurring of the absorption edge. Full article
(This article belongs to the Special Issue Quantum Crystals)
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Open AccessArticle Sliding Dynamics of Parallel Graphene Sheets: Effect of Geometry and Van Der Waals Interactions on Nano-Spring Behavior
Crystals 2018, 8(4), 149; doi:10.3390/cryst8040149
Received: 15 February 2018 / Revised: 20 March 2018 / Accepted: 22 March 2018 / Published: 28 March 2018
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Abstract
Graphene and carbon nanotubes are promising materials for nanoelectromechanical systems. Among other aspects, a proper understanding of the sliding dynamics of parallel graphene sheets or concentric nanotubes is of crucial importance for the design of nano-springs. Here, we analytically investigate the sliding dynamics
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Graphene and carbon nanotubes are promising materials for nanoelectromechanical systems. Among other aspects, a proper understanding of the sliding dynamics of parallel graphene sheets or concentric nanotubes is of crucial importance for the design of nano-springs. Here, we analytically investigate the sliding dynamics between two parallel, rigid graphene sheets. In particular, the analysis focuses on configurations in which the distance between the sheets is kept constant and lower than the equilibrium interlayer spacing of graphite (unstable configurations). The aim is to understand how the interlayer force due to van der Waals interactions along the sliding direction changes with the geometrical characteristics of the configuration, namely size and interlayer spacing. Results show metastable equilibrium positions with completely faced sheets, namely a null force along the sliding direction, whereas net negative/positive forces arise when the sheets are approaching/leaving each other. This behavior resembles a molecular spring, being able to convert kinetic into potential energy (van der Waals potential), and viceversa. The amplitude of both storable energy and entrance/exit forces is found to be proportional to the sheet size, and inversely proportional to their interlayer spacing. This model could also be generalized to describe the behavior of configurations made of concentric carbon nanotubes, therefore allowing a rational design of some elements of carbon-based nanoelectromechanical systems. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessCommunication A Ca(II) Coordination Polymer of 2-Carboxybenzaldehyde: Synthesis, Crystal Structure, and Catalytic Activity in Oxidation of Benzyl Alcohol
Crystals 2018, 8(4), 150; doi:10.3390/cryst8040150
Received: 6 March 2018 / Revised: 22 March 2018 / Accepted: 28 March 2018 / Published: 29 March 2018
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Abstract
The coordination polymers constructed by carboxylate ligand have shown novel structures and excellent properties. Therefore, a new Ca(II) coordination polymer with 2-carboxybenzaldehyde ligand, [Ca(L)2(H2O)2]n (L = 2-carboxybenzaldehyde), has been synthesized. Its structure has been identified by
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The coordination polymers constructed by carboxylate ligand have shown novel structures and excellent properties. Therefore, a new Ca(II) coordination polymer with 2-carboxybenzaldehyde ligand, [Ca(L)2(H2O)2]n (L = 2-carboxybenzaldehyde), has been synthesized. Its structure has been identified by elemental analysis, FT-IR, and single-crystal X-ray diffraction technique. The Ca(II) coordination polymer exhibits a 1D chained structure by the bridging effect of carboxylate groups. The Ca(II) coordination polymer exhibited relatively good catalytic activity in the benzyl alcohol oxidation reaction with benzyl alcohol conversion (53.8%) and moderate benzaldehyde selectivity (83.3%). Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Role of Bis(triphenylphosphine)iminium Cation [PNP]+ on the Crystal Packing of [PNP]+[HSeO3] Solvate Salt
Crystals 2018, 8(4), 151; doi:10.3390/cryst8040151
Received: 14 March 2018 / Revised: 23 March 2018 / Accepted: 28 March 2018 / Published: 29 March 2018
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Abstract
Selenate(IV) and hydrogen selenate(IV) salts of bulky cations are very interesting compounds for synthetic and kinetic studies. In this work, bis(triphenylphosphine)iminium ([PNP]+) chloride has been used, which aims to synthesize the corresponding selenate(IV) salt by an exchange reaction in the aqueous
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Selenate(IV) and hydrogen selenate(IV) salts of bulky cations are very interesting compounds for synthetic and kinetic studies. In this work, bis(triphenylphosphine)iminium ([PNP]+) chloride has been used, which aims to synthesize the corresponding selenate(IV) salt by an exchange reaction in the aqueous solution and subsequent crystallization by solvent evaporation. Unexpectedly, the procedure afforded a solvate form of the [PNP]+[HSeO3] salt (1). In this solid phase, which has a structure that is determined by Single Crystal XRD, the anion tends to maximize the interactions with itself, although it leaves the cationic moiety to have only weak interactions with the anions and the solvent molecules. In turn, the latter builds a network of effective hydrogen bonds. This behavior opposes the general tendency of selenite(IV) and hydrogen selenite(IV) compounds, since these anions are commonly found to have formed effective hydrogen bonds with surrounding chemical species. Moreover, as the exchange reaction is non-quantitative, the exceeding traces of the starting bis(triphenylphosphine)iminium chloride reagent reacted with bis(acetonitrile)dichloropalladium(II) to form the bis(triphenylphosphine)iminium hexachloropalladate (2). In the solid phase, [PNP]+ causes the absence of strong supramolecular interactions, which highlights the peculiar behavior of the cation in the crystal packing of its solid phases. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessArticle Morphology Transition of ZnO Nanorod Arrays Synthesized by a Two-Step Aqueous Solution Method
Crystals 2018, 8(4), 152; doi:10.3390/cryst8040152
Received: 21 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 30 March 2018
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Abstract
ZnO nanorod arrays (ZNAs) with vertically-aligned orientation were obtained by a two-step aqueous solution method. The morphology of the ZnO nanorods was regulated by changing the precursor concentration and the growth time of each step. ZnO nanorods with distinct structures, including flat top,
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ZnO nanorod arrays (ZNAs) with vertically-aligned orientation were obtained by a two-step aqueous solution method. The morphology of the ZnO nanorods was regulated by changing the precursor concentration and the growth time of each step. ZnO nanorods with distinct structures, including flat top, cone top, syringe shape, and nail shape, were obtained. Moreover, based on the X-ray diffraction (XRD) and the transmission electron microscope (TEM) analysis, the possible growth mechanisms of different ZnO nanostructrues were proposed. The room-temperature PL spectra show that the syringe-shaped ZNAs with ultra-sharp tips have high crystalline quality. Our study provides a simple and repeatable method to regulate the morphology of the ZNAs. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessArticle Zinc Oxide Nanostructures: From Chestnut Husk-Like Structures to Hollow Nanocages, Synthesis and Structure
Crystals 2018, 8(4), 153; doi:10.3390/cryst8040153
Received: 1 March 2018 / Revised: 14 March 2018 / Accepted: 28 March 2018 / Published: 30 March 2018
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Abstract
Tailor-made nanostructured ZnO cages have been catalytically grown on Au and Pt films covering silicon substrates, by a controlled evaporation process, which means an accurate choice of temperatures, times, gas flows (He in the heating, He/air during the synthesis), and Au/Pt film thickness.
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Tailor-made nanostructured ZnO cages have been catalytically grown on Au and Pt films covering silicon substrates, by a controlled evaporation process, which means an accurate choice of temperatures, times, gas flows (He in the heating, He/air during the synthesis), and Au/Pt film thickness. The effect of the process parameters affecting the morphology and the structure of the obtained materials has been investigated by XRD analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM) microscopies, and FTIR spectroscopies. In particular, the role of the synthesis temperature in affecting the size and shape of the obtained ZnO cages has been highlighted. It will be shown that by adopting higher temperatures, the protruding nanowhiskers several microns in length, covering the cages and exhibiting both basal and prismatic faces, change into very thin and narrow structures, with extended prismatic faces, prevailing with respect to the basal ones. At an even higher process temperature, the building up of Au particles aggregates inside and/or anchored to the walls of the hollow cages, without any evidence of elongated ZnO nanostructures will be highlighted. From FTIR spectra information on lattice modes of the investigated ZnO, materials have been obtained. Full article
(This article belongs to the collection Nanocrystals)
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Open AccessCommunication Structural and Luminescent Properties of Heterobimetallic Zinc(II)-Europium(III) Dimer Constructed from N2O2-Type Bisoxime and Terephthalic Acid
Crystals 2018, 8(4), 154; doi:10.3390/cryst8040154
Received: 8 March 2018 / Revised: 29 March 2018 / Accepted: 30 March 2018 / Published: 2 April 2018
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Abstract
A new heterohexanuclear ZnII–EuIII dimer [{(ZnL)2Eu}2(bdc)2]·2Cl constructed from a N2O2-type chelating ligand H2L (6,6′-Dimethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), Zn(OAc)2·2H2O, EuCl3·6H2O and H2bdc
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A new heterohexanuclear ZnII–EuIII dimer [{(ZnL)2Eu}2(bdc)2]·2Cl constructed from a N2O2-type chelating ligand H2L (6,6′-Dimethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), Zn(OAc)2·2H2O, EuCl3·6H2O and H2bdc (terephthalic acid) was synthesized, and characterized using elemental analyses, IR (Infrared), UV-Vis (Ultraviolet–visible) spectra and X-ray single crystal diffraction method. There are two crystallographically equivalent [(ZnL)2Eu] moieties in the ZnII–EuIII complex, the two [(ZnL)2Eu] moieties are linked by two bdc2– ligand leading to a heterohexanuclear dimer, in which the carboxylato groups bridge the ZnII and EuIII atoms. Furthermore, the luminescence properties of H2L and its ZnII–EuIII complex have been studied. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Cobalt(II) Terpyridin-4′-yl Nitroxide Complex as an Exchange-Coupled Spin-Crossover Material
Crystals 2018, 8(4), 155; doi:10.3390/cryst8040155
Received: 2 March 2018 / Revised: 26 March 2018 / Accepted: 29 March 2018 / Published: 2 April 2018
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Abstract
Spin-crossover (SCO) was studied in [Co(L)2](CF3SO3)2, where L stands for diamagnetic 2,2′:6′,2′′-terpyridine (tpy) and its paramagnetic derivative, 4′-{4-tert-butyl(N-oxy)aminophenyl}-substituted tpy (tpyphNO). The X-ray crystallographic analysis clarified the Co-N bond length change (Δ
[...] Read more.
Spin-crossover (SCO) was studied in [Co(L)2](CF3SO3)2, where L stands for diamagnetic 2,2′:6′,2′′-terpyridine (tpy) and its paramagnetic derivative, 4′-{4-tert-butyl(N-oxy)aminophenyl}-substituted tpy (tpyphNO). The X-ray crystallographic analysis clarified the Co-N bond length change (Δd) in high- and low-temperature structures; Δdcentral = 0.12 and Δddistal = 0.05 Å between 90 and 400 K for L = tpy and Δdcentral = 0.11 and Δddistal = 0.06 Å between 90 and 300 K for L = tpyphNO. The low- and high-temperature structures can be assigned to approximate low- and high-spin states, respectively. The magnetic susceptibility measurements revealed that the χmT value of [Co(tpyphNO)2](CF3SO3)2 had a bias from that of [Co(tpy)2](CF3SO3)2 by the contribution of the two radical spins. The tpy compound showed a gradual SCO around 260 K and on cooling the χmT value displayed a plateau down to 2 K. On the other hand, the tpyphNO compound showed a relatively abrupt SCO at ca. 140 K together with a second decrease of the χmT value on further cooling below ca. 20 K. From the second decrease, Co-nitroxide exchange coupling was characterized as antiferromagnetic with 2JCo-rad/kB = −3.00(6) K in the spin-Hamiltonian H = −2JCo-rad(SCo·Srad1 + SCo·Srad2). The magnetic moment apparently switches double-stepwise as 1 μB 3 μB 5 μB by temperature stimulus. Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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Open AccessArticle Resolution Dependence of an Ab Initio Phasing Method in Protein X-ray Crystallography
Crystals 2018, 8(4), 156; doi:10.3390/cryst8040156
Received: 17 February 2018 / Revised: 30 March 2018 / Accepted: 31 March 2018 / Published: 3 April 2018
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Abstract
For direct phasing of protein crystals, a method based on the hybrid-input-output (HIO) algorithm has been proposed and tested on a variety of structures. So far, however, the diffraction data have been limited to high-resolution ones, i.e., higher than 2 Å. In principle,
[...] Read more.
For direct phasing of protein crystals, a method based on the hybrid-input-output (HIO) algorithm has been proposed and tested on a variety of structures. So far, however, the diffraction data have been limited to high-resolution ones, i.e., higher than 2 Å. In principle, the methodology can be applied to data of lower resolutions, which might be particularly useful for phasing membrane protein crystals. For resolutions higher than 3.5 Å, it seems the atomic structure is solvable. For data of lower resolutions, information of the secondary structures and the protein boundary can still be obtained. Examples are given to support the conclusions. Real experimental data are used. Two aspects of the observed data have been discussed: removal of the measured low-resolution reflections and involvement of the unmeasured high-resolution reflections. The ab initio phasing employs histogram matching for density modification. A question arises whether the reference histogram used should match the resolution of the diffraction data or not. It seems that there is an optimal histogram which is good to use for data at various resolutions. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle (BEDT-TTF)2Cu2(CN)3 Spin Liquid: Beyond the Average Structure
Crystals 2018, 8(4), 158; doi:10.3390/cryst8040158
Received: 27 February 2018 / Revised: 29 March 2018 / Accepted: 30 March 2018 / Published: 4 April 2018
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Abstract
We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to
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We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to correctly and precisely determine it. The results of our work provide evidence that the structure presents a triclinic symmetry with two non-equivalent dimers in the unit cell, which implies a charge disproportionation between the dimers. However, structural refinement shows that the charge disproportionation is quite weak at room temperature. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle Interaction of Edge Dislocations with Graphene Nanosheets in Graphene/Fe Composites
Crystals 2018, 8(4), 160; doi:10.3390/cryst8040160
Received: 1 February 2018 / Revised: 30 March 2018 / Accepted: 1 April 2018 / Published: 4 April 2018
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Abstract
Graphene is an ideal reinforcement material for metal-matrix composites owing to its exceptional mechanical properties. However, as a 2D layered material, graphene shows highly anisotropic behavior, which greatly affects the mechanical properties of graphene-based composites. In this study, the interaction between an edge
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Graphene is an ideal reinforcement material for metal-matrix composites owing to its exceptional mechanical properties. However, as a 2D layered material, graphene shows highly anisotropic behavior, which greatly affects the mechanical properties of graphene-based composites. In this study, the interaction between an edge dislocation (b = 1/2 (111)) and a pair of graphene nanosheets (GNSs) in GNS reinforced iron matrix composite (GNS/Fe) was investigated using molecular dynamic simulations under simple shearing conditions. We studied the cases wherein the GNS pair was parallel to the (1 1 ¯ 0), (11 2 ¯ ), and (111) planes, respectively. The results showed that the GNS reinforcement can effectively hinder dislocation motion, which improves the yield strength. The interaction between the edge dislocation and the GNS pair parallel to the (11 2 ¯ ) plane showed the strongest effect of blocking dislocations among the three cases, resulting in increases in the shear modulus and yield stress of 107% and 1400%, respectively. This remarkable enhancement was attributed to the Orowan “by-passing” strengthening mechanism, whereas cross-slip of dislocation segments was observed during looping around GNSs. Our results might contribute to the development of high-strength iron matrix composites. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle High-Density Hydrogen Storage in a 2D-Matrix from Graphene Nanoblisters: A Prospective Nanomaterial for Environmentally Friendly Technologies
Crystals 2018, 8(4), 161; doi:10.3390/cryst8040161
Received: 31 January 2018 / Revised: 1 April 2018 / Accepted: 2 April 2018 / Published: 6 April 2018
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Abstract
In this paper, the atomic structure and mechanical stability of a new structural graphene modification—a 2D matrix of nanoscale cells in the form of a few-layer graphene substrate and nanoblister of a graphene monolayer—were studied for the first time. It is shown that
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In this paper, the atomic structure and mechanical stability of a new structural graphene modification—a 2D matrix of nanoscale cells in the form of a few-layer graphene substrate and nanoblister of a graphene monolayer—were studied for the first time. It is shown that such matrices are mechanically stable and are promising for environmentally friendly technologies. The calculated local atomic stress fields demonstrate that the atomic framework is not destroyed, even in the presence of defects in the atomic network of graphene nanoblister (Stone-Wales defect, double vacancies defect, ad-dimmer defect, and their combination). However, it was established that the presence of one or more SW defects leads to the appearance of critical stresses. These critical stresses can induce local bond breaking in the atomic network with an increase in temperature or external pressure. It was found that graphene nanoblister can store molecular hydrogen with a maximum density of 6.6 wt % for 1158 m2/g at 77 K under normal pressure. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Tuning of Luminescent and Magnetic Properties via Metal Doping of Zn-BTC Systems
Crystals 2018, 8(4), 162; doi:10.3390/cryst8040162
Received: 18 March 2018 / Revised: 2 April 2018 / Accepted: 5 April 2018 / Published: 8 April 2018
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Abstract
In order to assess how metal doping affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me2NH2+} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M
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In order to assess how metal doping affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me2NH2+} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M1-M2-BTC}{Me2NH2+} (M1 = Co, Cu; M2 = Ni, Co) were synthesized. Trace amounts of different metals were doped via addition of another metal salt during the synthetic process. All compounds retained the same crystal structure as that of the parent {Zn-BTC}{Me2NH2+} MOF, which was supported by single crystal and powder X-ray diffraction studies. Thermal Gravimetric Analysis (TGA) of these compounds also revealed that all MOFs had similar stability up to ~450 °C. Solid state photoluminescent studies indicated that {Zn-Mn-BTC}{Me2NH2+}, {Zn-Cd-BTC}{Me2NH2+}, and {Zn-Ca-BTC}{Me2NH2+} had a significant red shifting effect compared to the original {Zn-BTC}{Me2NH2+} MOF. Applications of this doping method to other MOF systems can provide an efficient way to tune the luminescence of such systems, and to obtain a desired wavelength for several applications such as sensors and white light LED materials. Because Zn, Co, Cu, Ni, Mg have magnetic properties, the effect of the doping metal atom on the magnetism of the {Zn-BTC}{Me2NH2+} networks was also studied. To characterize the magnetic behavior of the synthesized MOFs, we conducted low-temperature (10 K) saturation remanence experiments in a 3 Tesla applied field, with the principal goal of identifying the domain state of the synthesized materials (Zn, Zn-Co, Zn-Cu-Co, Zn-Cu-Ni, Zn-Mg, Zn-Mn, Zn-Ni-Co, Zn-Ni). During room/low temperature saturation magnetization experiments, Zn, Zn-Co, Zn-Cu-Co, and Zn-Cu-Ni systems yielded data indicative of superparamagnetic behavior, yet during zero field and field cooled experiments Zn-Co showed a slight paramagnetic effect, Zn showed no temperature dependence on warming and Zn-Cu-Co and Zn-Cu-Ni demonstrated only a slight temperature dependence on warming. These behaviors are consistent with ferromagnetic ordering. Zero field and field cooled experiments indicate that Zn-Mg and Zn-Ni have a ferromagnetic ordering and Zn-Mn and Zn-Ni-Co show paramagnetic ordering behavior. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Pseudo-Bifurcated Chalcogen Bond in Crystal Engineering
Crystals 2018, 8(4), 163; doi:10.3390/cryst8040163
Received: 2 March 2018 / Revised: 2 April 2018 / Accepted: 6 April 2018 / Published: 9 April 2018
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Abstract
The concept of pseudo-bifurcated chalcogen bond has been proposed for the first time in this paper. It was found that the anticooperative effects between two chalcogen bonds of the pseudo-bifurcated chalcogen bond are not very large as compared to those of the true
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The concept of pseudo-bifurcated chalcogen bond has been proposed for the first time in this paper. It was found that the anticooperative effects between two chalcogen bonds of the pseudo-bifurcated chalcogen bond are not very large as compared to those of the true bifurcated noncovalent bond. According to the nature of pseudo-bifurcated chalcogen bond, we designed some strong pseudo-bifurcated chalcogen bond synthons. The binding energy of the strongest pseudo-bifurcated chalcogen bond attains about 27 kcal/mol. These strong pseudo-bifurcated chalcogen bond synthons have great potential as building blocks in crystal engineering. Full article
(This article belongs to the Special Issue Chalcogen Bonding in Crystalline and Catalyst Materials)
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Open AccessArticle Solid Phases Precipitating in Artificial Urine in the Absence and Presence of Bacteria Proteus mirabilis—A Contribution to the Understanding of Infectious Urinary Stone Formation
Crystals 2018, 8(4), 164; doi:10.3390/cryst8040164
Received: 12 March 2018 / Revised: 31 March 2018 / Accepted: 6 April 2018 / Published: 9 April 2018
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Abstract
Magnesium ammonium phosphate hexahydrate, called struvite, is the dominant component of infectious urinary stones. In addition to struvite, infectious urinary stones include solid phases with poor crystallinity as well as amorphous matter. This article is devoted to the analysis of these solid phases,
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Magnesium ammonium phosphate hexahydrate, called struvite, is the dominant component of infectious urinary stones. In addition to struvite, infectious urinary stones include solid phases with poor crystallinity as well as amorphous matter. This article is devoted to the analysis of these solid phases, because they have not been characterized well until now. The solid phases tested were obtained from artificial urine in the absence and presence of Proteus mirabilis. The solid phases were characterized by different techniques (X-ray Diffraction, Energy Dispersive X-ray, Scanning Electron Microscopy, as well as Raman and Infrared Spectroscopies). According to the results these phases are carbonate apatite (CA), hydroxylapatite (HAP), amorphous calcium carbonate (ACC), amorphous calcium phosphate (ACP) and/or amorphous carbonated calcium phosphate (ACCP). Carbonate apatite and hydroxylapatite may occur in non-stoichiometric forms, i.e., various anions can be substituted for CO32−, OH, and PO43− groups in them. The non-stoichiometry of carbonate apatite and hydroxylapatite also implies a deficiency of calcium ions, i.e., calcium ions may be partially replaced by other cations. Experimental techniques and chemical speciation analysis demonstrate that the presence of magnesium influences the formation of CA and HAP. Full article
(This article belongs to the Section Biomolecular Crystals)
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Open AccessArticle Synthesis, Crystal Structures, Optical Properties and Theoretical Calculations of Two Metal Chalcogenides Ba2AlSbS5 and Ba2GaBiSe5
Crystals 2018, 8(4), 165; doi:10.3390/cryst8040165
Received: 19 March 2018 / Revised: 8 April 2018 / Accepted: 9 April 2018 / Published: 13 April 2018
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Abstract
Two quaternary metal chalcogenides, Ba2AlSbS5 and Ba2GaBiSe5, were successfully synthesized by solid-state reaction in sealed silica tubes. Both of them crystallize in the same orthorhombic space group Pnma, but they appear with obviously different construction
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Two quaternary metal chalcogenides, Ba2AlSbS5 and Ba2GaBiSe5, were successfully synthesized by solid-state reaction in sealed silica tubes. Both of them crystallize in the same orthorhombic space group Pnma, but they appear with obviously different construction features. For example, Ba2AlSbS5 exhibits [SbS3]3− units and zero-dimensional (0D) [AlSbS5]4− clusters, which is different from those ([BiSe6]3− units and 1D [GaBiSe5]4− chains) of Ba2GaBiSe5. We also systematically investigated the entire series of Ba2MIIIMIII’Q5 (MIII = Al, Ga, In; MIII’ = As, Sb, Bi; Q = S, Se, Te) compounds, and the results showed that the interconnection of MIIIQ4 and MIII’Qn (n = 3, 5, 6) units can form three different structural types, including 0D [MIIIMIII’Q5] clusters, single [MIII’Q3] chains and isolated [MIIIQ4] units, or [MIIIQ3]n and [MIII’Q3]n double chains, which may be induced by the flexible coordination and on-link modes of MIII’ atoms. Spectral investigation shows that their bandgaps are about 2.57 eV for Ba2AlSbS5 and 2.14 eV for Ba2GaBiSe5. Theoretical calculation was also used to analyze their structure-property relationships, and the results indicate that the title compounds exhibit larger birefringences (Δn > 0.10), thus having potential as the IR birefringent materials. Full article
(This article belongs to the Special Issue Properties and Applications of Complex Chalcogenides)
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Open AccessArticle The Influence of Hydroxyl Groups on Friction of Graphene at Atomic Scale
Crystals 2018, 8(4), 167; doi:10.3390/cryst8040167
Received: 21 March 2018 / Revised: 10 April 2018 / Accepted: 13 April 2018 / Published: 16 April 2018
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Abstract
Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising
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Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising of hydroxyl groups ratio, and reaches the maximum when the hydroxyl groups ratio between interfaces is about 10%. The reason is that hydrogen bonds tend to form in interlayers when the hydroxyl groups ratio is high. The formed hydrogen bonds between interfaces are closely related to the friction. However, the analysis of the component of van der Waals, Coulomb’s forces and hydrogen bonds interaction between interfaces indicates that van der Waals forces are dominant in friction, which can be attributed to the influence of interface distance on friction. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Epitaxial Crystallization of Precisely Methyl-Substituted Polyethylene Induced by Carbon Nanotubes and Graphene
Crystals 2018, 8(4), 168; doi:10.3390/cryst8040168
Received: 9 March 2018 / Revised: 11 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional
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How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional nanocomposites with carbon nanotubes (CNTs) and graphene via solution crystallization. It is shown that kebab-like and rod-like nanofiller-induced crystals were separately observed on the surfaces of CNTs and graphene and the density of rod-like crystals is significantly less than kebab-like ones. The results of differential scanning calorimetry (DSC) and X-ray diffraction (XRD) reveal that CNTs and graphene cannot induce polymers with the substituent volume greater than, or equal to, 2 Å (methyl) to form ordered lattice structure, but CNTs exhibit the better nucleation effect, providing us with guidance to manipulate the physical performance of polymer composites on the basis of the size of the substituent and the type of nanofiller. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Crystal Structure, Spectroscopic Investigations, and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)
Crystals 2018, 8(4), 169; doi:10.3390/cryst8040169
Received: 1 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 16 April 2018
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Abstract
The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c
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The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c = 413.04(2) pm, wR2 = 0.0780, 942 F2 values, 46 variables) with space group Cmmm (oC48; q2pji2hedb). A comparison with the Pearson database indicated that YPt2Al3 forms a new structure type, in which the Pt and Al atoms form a [Pt2Al3]δ polyanion and the Y atoms reside in the cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi2Al3-type structure and the new YPt2Al3-type structure was illustrated. The compounds with RE = Dy–Tm were characterized by powder X-ray diffraction experiments. While YPt2Al3 is a Pauli-paramagnet, the other REPt2Al3 (RE = Dy–Tm) compounds exhibit paramagnetic behavior, which is in line with the rare-earth atoms being in the trivalent oxidation state. DyPt2Al3 and TmPt2Al3 exhibit ferromagnetic ordering at TC = 10.8(1) and 4.7(1) K and HoPt2Al3 antiferromagnetic ordering at TN = 5.5(1) K, respectively. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu2Pt3Al4 (Ce2Ir3Sb4-type, Pnma, a = 1343.4(2), b = 416.41(8), c = 1141.1(2) pm), which could also be realized with thulium. The structure was refined from single-crystal data (wR2 = 0.0940, 1605 F2 values, 56 variables). Again, a polyanion with bonding Pt–Al interactions was found, and the two distinct Lu atoms were residing in the cavities of the [Pt3Al4]δ framework. X-ray photoelectron spectroscopy (XPS) measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Quasi-Equilibrium, Multifoil Platelets of Copper- and Titanium-Substituted Bismuth Vanadate, Bi2V0.9(Cu0.1−xTix)O5.5−δ, by Molten Salt Synthesis
Crystals 2018, 8(4), 170; doi:10.3390/cryst8040170
Received: 11 March 2018 / Revised: 9 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
10% copper-substituted (BiCUVOX/Bi2V0.9Cu0.1O5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi2V0.9(Cu0.05Ti0.05)O5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The
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10% copper-substituted (BiCUVOX/Bi2V0.9Cu0.1O5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi2V0.9(Cu0.05Ti0.05)O5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The product was phase-pure within the limits of X-ray diffraction. The size and form of the platelets could be controlled by changing the heating temperature and time. The crystallite growth rate at a synthesis temperature of 650 °C and the activation energy for grain growth were determined for BICUTIVOX, which experienced inhibited growth compared to BICUVOX. Quasi-equilibrium, multifoil shapes consisting of lobes around the perimeter of the platelets were observed and explained in the context of relative two-dimensional nucleation and edge growth rates. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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Open AccessCommunication Crystal Structure of the Catalytic Domain of MCR-1 (cMCR-1) in Complex with d-Xylose
Crystals 2018, 8(4), 172; doi:10.3390/cryst8040172
Received: 4 March 2018 / Revised: 12 April 2018 / Accepted: 14 April 2018 / Published: 17 April 2018
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Abstract
The polymyxin colistin is known as a “last resort” antibacterial drug toward pandrug-resistant enterobacteria. The recently discovered plasmid-encoded mcr-1 gene spreads rapidly across pathogenic strains and confers resistance to colistin, which has emerged as a global threat. The mcr-1 gene encodes a phosphoethanolamine
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The polymyxin colistin is known as a “last resort” antibacterial drug toward pandrug-resistant enterobacteria. The recently discovered plasmid-encoded mcr-1 gene spreads rapidly across pathogenic strains and confers resistance to colistin, which has emerged as a global threat. The mcr-1 gene encodes a phosphoethanolamine transferase (MCR-1) that catalyzes the transference of phosphoethanolamine to lipid A moiety of lipopolysaccharide, resulting in resistance to colistin. Development of effective MCR-1 inhibitors is crucial for combating MCR-1-mediated colistin resistance. In this study, MCR-1 catalytic domain (namely cMCR-1) was expressed and co-crystallized together with d-xylose. X-ray crystallographic study at a resolution of 1.8 Å found that cMCR-1-d-xylose co-crystals fell under space group P212121, with unit-cell parameters a = 51.6 Å, b = 73.1 Å, c = 82.2 Å, α = 90°, β = 90°, γ = 90°. The asymmetric unit contained a single cMCR-1 molecule complexed with d-xylose and had a solvent content of 29.13%. The structural model of cMCR-1-d-xylose complex showed that a d-xylose molecule bound in the putative lipid A-binding pocket of cMCR-1, which might provide a clue for MCR-1 inhibitor development. Full article
(This article belongs to the Special Issue Biological Crystallization)
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Open AccessArticle Structures and Fluorescent and Magnetic Behaviors of Newly Synthesized NiII and CuII Coordination Compounds
Crystals 2018, 8(4), 173; doi:10.3390/cryst8040173
Received: 20 March 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Newly designed three trinuclear coordination compounds [Ni3(L1)2(OAc)2(CH3OH)2] (1), [Ni3(L1)2(OAc)2(CH3CH2CH2OH)2]·2CH3CH2CH
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Newly designed three trinuclear coordination compounds [Ni3(L1)2(OAc)2(CH3OH)2] (1), [Ni3(L1)2(OAc)2(CH3CH2CH2OH)2]·2CH3CH2CH2OH (2) and [Ni3(L1)2(OAc)2(DMF)2]·1.71DMF (3) and one mononuclear coordination compound [Cu(L2)2] (4) have been synthesized by H2L1 and nickel(II) and copper(II) acetate hydrates in different solvents. Single-crystal X-ray structure determinations revealed that the coordination compounds 13 have analogous molecular structures. The coordination compounds 1, 2, and 3 were affected by the coordinated methanol, n-propanol, and N,N-dimethylformamide molecules, respectively, and the various coordinated solvent molecules give rise to the formation of the representive solvent-induced NiII coordination compounds. All the NiII atoms are six-coordinated with geometries of slightly distorted octahedron. Obviously, in the coordination compound 4, the expected salamo-like mono- or tri-nuclear CuII coordination compound has not been obtained, but a new CuII coordination compound [Cu(L2)2] has been gained. The Cu1 atom is four-coordinated and possesses a geometry of slightly distorted planar quadrilateral. Furthermore, the fluorescence properties of coordination compounds 14 and magnetic behavior of coordination compound 1 were investigated. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessCommunication Hetero-Trinuclear CoII2-DyIII Complex with a Octadentate Bis(Salamo)-Like Ligand: Synthesis, Crystal Structure and Luminescence Properties
Crystals 2018, 8(4), 174; doi:10.3390/cryst8040174
Received: 28 March 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
A hetero-trinuclear CoII2-DyIII complex, [Co2L(DMF)2Dy(NO3)3]·C2H5O2 was synthesized via the reaction of a multi-naphthol-based bis(Salamo)-like tetraoxime H4L with Co(OAc)2·4H2O and Dy(NO
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A hetero-trinuclear CoII2-DyIII complex, [Co2L(DMF)2Dy(NO3)3]·C2H5O2 was synthesized via the reaction of a multi-naphthol-based bis(Salamo)-like tetraoxime H4L with Co(OAc)2·4H2O and Dy(NO3)3·6H2O, and fully characterized via elemental analyses, X-ray crystallography, FT-IR and UV-Vis spectra. In addition, luminescence properties of H4L and its CoII2-DyIII complex have also been investigated. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Probabilistic Estimate of |Foa| from FEL Data
Crystals 2018, 8(4), 175; doi:10.3390/cryst8040175
Received: 28 February 2018 / Revised: 27 March 2018 / Accepted: 9 April 2018 / Published: 18 April 2018
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Abstract
The method of the joint probability distribution function was applied in order to estimate the normal structure factor amplitudes of the anomalous scatterer substructure in a FEL experiment. The two-wavelength case was examined. In this, the prior knowledge of the moduli |F
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The method of the joint probability distribution function was applied in order to estimate the normal structure factor amplitudes of the anomalous scatterer substructure in a FEL experiment. The two-wavelength case was examined. In this, the prior knowledge of the moduli | F 1 + | , | F 1 | , | F 2 + | , | F 2 | was used to predict the value of | F 0 a | , which is the structure factor amplitude arising from the normal scattering of the heavy atom anomalous scatterers. The mathematical treatment provides a solid theoretical basis for the RIP (Radiation-damage Induced Phasing) method, which was originally proposed in order to take the radiation damage induced by synchrotron radiation sources into account. This was further adapted to exploit FEL data, where the crystal damage is usually more massive. Full article
Open AccessArticle Solvent-Induced Unsymmetric Salamo-Like Trinuclear NiII Complexes: Syntheses, Crystal Structures, Fluorescent and Magnetic Properties
Crystals 2018, 8(4), 176; doi:10.3390/cryst8040176
Received: 26 March 2018 / Revised: 14 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Solvent-induced trinuclear NiII complexes, [{Ni(L)(MeOH)}2(OAc)2Ni]·2MeOH (1), [{Ni(L)(EtOH)}2(OAc)2Ni]·2H2O (2), [{Ni(L)(n-PrOH)}2(OAc)2Ni]·2H2O (3) and [{Ni(L)(i-PrOH)}2(OAc)2Ni]
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Solvent-induced trinuclear NiII complexes, [{Ni(L)(MeOH)}2(OAc)2Ni]·2MeOH (1), [{Ni(L)(EtOH)}2(OAc)2Ni]·2H2O (2), [{Ni(L)(n-PrOH)}2(OAc)2Ni]·2H2O (3) and [{Ni(L)(i-PrOH)}2(OAc)2Ni] (4), have been prepared with an unsymmetric Salamo-like ligand H2L, and characterized via X-ray crystallography, FT-IR, UV-Vis and fluorescence spectra. In complexes 1, 2, 3 and 4, there are two ligand (L)2− moieties, two acetato ligands, two coordinated methanol, ethanol, n-propanol or i-propanol molecules, respectively, as well as other crystallizing solvent molecules. Two acetato ligands coordinated to the three NiII ions via usual Ni-O-C-O-Ni bridges, and four µ-phenoxo oxygen atoms coming from two [NiL(solvent)] units coordinate to the central NiII ions. Although different solvents are induced in the complexes, all the NiII ions are six-coordinated and adopt geometries of distorted octahedron. Magnetic measurements were performed on complex 2, an intramolecular antiferromagnetic interaction was observed between NiII ions and a simulation of the experimental data gives J = −2.96 cm−1 and g = 2.30. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Analysis of Leaky Modes in Photonic Crystal Fibers Using the Surface Integral Equation Method
Crystals 2018, 8(4), 177; doi:10.3390/cryst8040177
Received: 1 March 2018 / Revised: 14 April 2018 / Accepted: 14 April 2018 / Published: 19 April 2018
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Abstract
A fully vectorial algorithm based on the surface integral equation method for the modelling of leaky modes in photonic crystal fibers (PCFs) by solely solving the complex propagation constants of characteristic equations is presented. It can be used for calculations of the complex
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A fully vectorial algorithm based on the surface integral equation method for the modelling of leaky modes in photonic crystal fibers (PCFs) by solely solving the complex propagation constants of characteristic equations is presented. It can be used for calculations of the complex effective index and confinement losses of photonic crystal fibers. As complex root examination is the key technique in the solution, the new algorithm which possesses this technique can be used to solve the leaky modes of photonic crystal fibers. The leaky modes of solid-core PCFs with a hexagonal lattice of circular air-holes are reported and discussed. The simulation results indicate how the confinement loss by the imaginary part of the effective index changes with air-hole size, the number of rings of air-holes, and wavelength. Confinement loss reductions can be realized by increasing the air-hole size and the number of air-holes. The results show that the confinement loss rises with wavelength, implying that the light leaks more easily for longer wavelengths; meanwhile, the losses are decreased significantly as the air-hole size d/Λ is increased. Full article
(This article belongs to the Special Issue Photonic Crystal Fiber)
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Open AccessArticle Characterization of Sub-Monolayer Contaminants at the Regrowth Interface in GaN Nanowires Grown by Selective-Area Molecular Beam Epitaxy
Crystals 2018, 8(4), 178; doi:10.3390/cryst8040178 (registering DOI)
Received: 22 March 2018 / Revised: 10 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
While GaN nanowires (NWs) offer an attractive architecture for a variety of nanoscale optical, electronic, and mechanical devices, defects such as crystal polarity inversion domains (IDs) can limit device performance. Moreover, the formation of such defects during NW growth is not fully understood.
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While GaN nanowires (NWs) offer an attractive architecture for a variety of nanoscale optical, electronic, and mechanical devices, defects such as crystal polarity inversion domains (IDs) can limit device performance. Moreover, the formation of such defects during NW growth is not fully understood. In this study, we use transmission electron microscopy (TEM) and atom probe tomography (APT) to investigate the effects of sub-monolayer contamination at the regrowth interface in GaN NWs grown by selective-area molecular beam epitaxy (MBE). TEM energy dispersive X-ray spectroscopy (EDS) and APT independently identified Al and O contamination localized at the regrowth interface in two of the three growth runs examined. The Al and O concentrations were each estimated to be on the order of 11% of an ideal c-plane monolayer in the most severely contaminated case. The amount of contamination correlated with the number of crystal polarity inversion domain defects (IDs) across the growth runs. A growth run in which the pre-regrowth HF vapor etch step was replaced by HCl immersion showed the smallest quantity of O and no measurable Al. In addition, many of the NWs examined from the HCl-treated growth run turned out to be free of IDs. These results suggest that sub-monolayer contamination introduced during processing contributes to defect formation in MBE-grown GaN NWs. Full article
(This article belongs to the Special Issue Growth and Structural Characterization of Self-Nucleated Nanowires)
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Open AccessArticle Size Control of Cobalt-Doped ZnO Nanoparticles Obtained in Microwave Solvothermal Synthesis
Crystals 2018, 8(4), 179; doi:10.3390/cryst8040179
Received: 13 February 2018 / Revised: 9 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor.
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This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor. It has been proved by the example of Zn0.9Co0.1O NPs (x = 10 mol %) that by controlling the water quantity in the precursor it is possible to precisely control the size of the obtained Zn1−xCoxO NPs. The following properties of the obtained Zn0.9Co0.1O NPs were tested: skeleton density (helium pycnometry), specific surface area (BET), dopant content (ICP-OES), morphology (SEM), phase purity (XRD), lattice parameter (Rietveld method), average crystallite size (FW1/5/4/5M method and Scherrer’s formula), crystallite size distribution (FW1/5/4/5M method), and average particle size (from TEM and SSA). An increase in the water content in the precursor between 1.5% and 5% resulted in the increase in Zn0.9Co0.1O NPs size between 28 nm and 53 nm. The X-ray diffraction revealed the presence of only one hexagonal phase of ZnO in all samples. Scanning electron microscope images indicated an impact of the increase in water content in the precursor on the change of size and shape of the obtained Zn0.9Co0.1O NPs. The developed method of NPs size control in the microwave solvothermal synthesis was used for the first time for controlling the size of Zn1−xCoxO NPs. Full article
(This article belongs to the Special Issue Microwave-Assisted Synthesis of Nanocrystals and Nanostructures)
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Open AccessArticle Ferroelectric Relaxor Quantum Crystals
Crystals 2018, 8(4), 180; doi:10.3390/cryst8040180 (registering DOI)
Received: 27 February 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
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Abstract
A discussion is given of ferroelectrics (FEs) that have their Curie temperatures Tc very near absolute zero. These have differences in their dynamics in comparison with higher-temperature systems, since domain wall motion occurs via quantum mechanical tunneling and not by thermally activated
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A discussion is given of ferroelectrics (FEs) that have their Curie temperatures Tc very near absolute zero. These have differences in their dynamics in comparison with higher-temperature systems, since domain wall motion occurs via quantum mechanical tunneling and not by thermally activated diffusion. Emphasis in the present paper is on FEs that have relaxor characteristics. In such systems, the temperature at which the isothermal electric susceptibility ε(T,f) peaks is a strong function of frequency, and it decreases with decreasing frequency. This is due to glassy viscosity and is symbolic of non-equilibrium dynamics, usually described by a Vogel-Fulcher equation. It permits an extra dimension with which to examine the transitions. The second half of this paper reviews domain wall instabilities and asks about their presence in QCP ferroelectrics, which has not yet been reported and may be unobservable due to the absence of thermal diffusion of walls near T = 0; in this respect, we note that diffusion does exist in ferroelectric relaxors, even at T = 0, by virtue of their glassy, viscous dynamics. Full article
(This article belongs to the Special Issue Quantum Crystals)
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Review

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Open AccessReview Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control
Crystals 2018, 8(4), 143; doi:10.3390/cryst8040143
Received: 24 February 2018 / Revised: 18 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF)2X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive
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This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF)2X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive phase appears depending on the Coulomb repulsion U and the bandwidth W, which is tunable by external and chemical pressures. First, we report the high-pressure ac (alternating current) calorimetry technique and experimental system constructed to measure single-crystal samples of molecule-based compounds to derive low-temperature thermodynamic parameters. Using extremely small resistance chips as a heater and a thermometer allows four-terminal detection of an accurate temperature and its oscillation in the sample part with sufficient sensitivity. From the analyses of the temperature dependence of the ac heat capacity of κ-(BEDT-TTF)2Cu(NCS)2 under external pressures, we discuss the changes in the peak shape of the thermal anomaly at the superconductive transition temperature Tc at various external pressures p. The rather sharp peak in CpT−1 at Tc = 9.1 K with a strong coupling character at ambient pressure is gradually reduced to weaker coupling as the pressure increases to 0.45 GPa concomitant with suppression of the transition temperature. This feature is compared with the systematic argument of the chemical–pressure effect on the basis of thermal anomalies around the superconductive transition of κ-(BEDT-TTF)2X compounds and other previously studied typical dimer-Mott 2:1 compounds. Finally, the discussion is extended to the chemical pressure effect on the normal state electronic heat capacity coefficient γ obtained by applying magnetic fields higher than Hc2 and the residual γ*, which remains in the superconductive state due to the induced electron density of states around the node structure. From the overall arguments with respect to both chemical and external pressures, we suggest that a crossover of the electronic state inside the superconductive phase occurs and the coupling strength of electron pairs varies from the electron correlation region near the metal-insulator boundary to the band picture region. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessReview Radiation Damage in Macromolecular Crystallography—An Experimentalist’s View
Crystals 2018, 8(4), 157; doi:10.3390/cryst8040157
Received: 5 March 2018 / Revised: 22 March 2018 / Accepted: 24 March 2018 / Published: 4 April 2018
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Abstract
Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K),
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Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K), which can lead to incorrect biological conclusions being drawn from the resulting structure, or even prevent structure solution entirely. Investigation of mitigation strategies and the effects caused by radiation damage has been extensive over the past fifteen years. Here, recent understanding of the physical and chemical phenomena of radiation damage is described, along with the global effects inflicted on the collected data and the specific effects observed in the solved structure. Furthermore, this review aims to summarise the progress made in radiation damage studies in macromolecular crystallography from the experimentalist’s point of view and to give an introduction to the current literature. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessReview Transition Metal Selenite Halides: A Fascinating Family of Magnetic Compounds
Crystals 2018, 8(4), 159; doi:10.3390/cryst8040159
Received: 12 March 2018 / Revised: 31 March 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
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Abstract
The problem of searching for low-dimensional magnetic systems has been a topical subject and has attracted attention of the chemistry and physics community for the last decade. In low-dimensional magnetic systems, magnetic ions are distributed anisotopically and form different groups such as dimers,
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The problem of searching for low-dimensional magnetic systems has been a topical subject and has attracted attention of the chemistry and physics community for the last decade. In low-dimensional magnetic systems, magnetic ions are distributed anisotopically and form different groups such as dimers, chains, ladders, or planes. In 3D frameworks, the distances between magnetic ions are equal in all directions while in low-dimensional systems the distances within groups are different from those between groups. The main approach of searching for desired systems is a priori crystal chemical design expecting the needed distribution of transition metal ions in the resulting structure. One of the main concepts of this structural design is the incorporation of the p-element ions with stereochemically active electron pairs and ions acting as spacers in the composition. Transition metal selenite halides, substances that combine SeO32− groups and halide ions in the structure, seem to be a promising object of investigation. Up to now, there are 33 compounds that are structurally described, magnetically characterized, and empirically tested on different levels. The presented review will summarize structural peculiarities and observed magnetic properties of the known transition metal selenite halides. In addition, the known compounds will be analyzed as possible low-dimensional magnetic systems. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessReview Low-Frequency Dynamics of Strongly Correlated Electrons in (BEDT-TTF)2X Studied by Fluctuation Spectroscopy
Crystals 2018, 8(4), 166; doi:10.3390/cryst8040166
Received: 22 March 2018 / Revised: 5 April 2018 / Accepted: 8 April 2018 / Published: 14 April 2018
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Abstract
Fluctuation spectroscopy measurements of quasi-two-dimensional organic charge-transfer salts (BEDT-TTF)2X are reviewed. In the past decade, the method has served as a new approach for studying the low-frequency dynamics of strongly correlated charge carriers in these materials. We review some basic aspects
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Fluctuation spectroscopy measurements of quasi-two-dimensional organic charge-transfer salts (BEDT-TTF) 2 X are reviewed. In the past decade, the method has served as a new approach for studying the low-frequency dynamics of strongly correlated charge carriers in these materials. We review some basic aspects of electronic fluctuations in solids, and give an overview of selected problems where the analysis of 1 / f -type fluctuations and the corresponding slow dynamics provide a better understanding of the underlying physics. These examples are related to (1) an inhomogeneous current distribution due to phase separation and/or a percolative transition; (2) slow dynamics due to a glassy freezing either of structural degrees of freedom coupling to the electronic properties or (3) of the electrons themselves, e.g., when residing on a highly-frustrated crystal lattice, where slow and heterogeneous dynamics are key experimental properties for the vitrification process of a supercooled charge-liquid. Another example is (4), the near divergence and critical slowing down of charge carrier fluctuations at the finite-temperature critical endpoint of the Mott metal-insulator transition. Here also indications for a glassy freezing and temporal and spatial correlated dynamics are found. Mapping out the region of ergodicity breaking and understanding the influence of disorder on the temporal and spatial correlated fluctuations will be an important realm of future studies, as well as the fluctuation properties deep in the Mott or charge-ordered insulating states providing a connection to relaxor or ordered ferroelectric states studied by dielectric spectroscopy. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessReview Optoelectronics Based Dynamic Advancement of Graphene: Characteristics and Applications
Crystals 2018, 8(4), 171; doi:10.3390/cryst8040171
Received: 28 February 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing
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Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing day by day. This two-dimensional material (2D) is using mellifluously for the development in different types of devices in the field of optics, photonics, light emitting diode (LED), medical diagnosis, sensing, and so on. In this review, the relevant optical properties and the applications areas with available results in various fields are discussed. Again, the optical conductivity of strained graphene is reviewed in a wavelength related regime that depends on strain modulus and position with field arrangements. Graphene shows a saturation and reverse saturation process due to the increase of light intensity. In addition, strong absorption is observed from the visible to mid-infrared (MIR) wavelength range. Moreover, the application areas of graphene including optics, photonics, plasmonics, mode-locked laser, optical modulator, etc., and the comparison of various results obtained from different sources are presented. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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