Open AccessFeature PaperArticle
Synthesis, Crystal Structure Analysis and Decomposition of RbAlH4
Crystals 2018, 8(2), 103; doi:10.3390/cryst8020103 -
Abstract
RbAlH4, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The
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RbAlH4, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD4 is isostructural to KAlD4. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides. Full article
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Open AccessArticle
Atomic-Site-Specific Analysis on Out-of-Plane Elasticity of Convexly Curved Graphene and Its Relationship to sp2 to sp3 Re-Hybridization
Crystals 2018, 8(2), 102; doi:10.3390/cryst8020102 -
Abstract
The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties
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The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties of graphene under compressing and stretching deformations have been exclusively investigated by local-probe techniques. Here we report that the interatomic attractive force introduced by atomic force microscopy triggers “single”-atom displacement and consequently enables us to determine out-of-plane elasticities of convexly curved graphene including its atomic-site-specific variation. We have quantitatively evaluated the relationship between the out-of-plane displacement and elasticity of convexly curved graphene by three-dimensional force field spectroscopy on a side-wall of a hollow tube with a well-defined curvature. The substantially small intrinsic modulus that complies with continuum mechanics has been found to increase significantly at atomically specific locations, where sp2 to sp3 re-hybridization would certainly take place. Full article
Open AccessReview
Drug‑Drug and Drug‑Nutraceutical Cocrystal/Salt as Alternative Medicine for Combination Therapy: A Crystal Engineering Approach
Crystals 2018, 8(2), 101; doi:10.3390/cryst8020101 -
Abstract
The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them
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The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them one of the potential alternatives when salt preparation is not feasible. Apart from generally regarded as safe (GRAS) coformers, drug‑drug and drug‑nutraceutical cocrystals are recent additions to pharmaceutical cocrystal family that have additional health benefits. Indeed, preparation of salt forms is a routine practice to deal with inadequacies associated with the active pharmaceutical ingredient (API) and happens to be a potentially reliable method. Amongst them, drug-drug and drug-nutraceutical cocrystals have drawn significant importance in the recent past as they reduce drug load and cost effects during multiple disease diagnosis. However, one has to be prudent in the selection of drug molecules, the presence of complementary hydrogen bond synthon, disease management during multiple disease therapy, etc. that play important roles in their preparation. That is the reason why drug–drug cocrystals are scarce in the literature compared to pharmaceutical cocrystals containing GRAS coformers and salt forms. Herein, we discuss case studies preferably the reported drug‑drug, drug‑nutraceutical cocrystals, and a few salts with an emphasis on their role in physicochemical property modulation. Full article
Open AccessArticle
Incorporation of Hexanuclear Mn(II,III) Carboxylate Clusters with a {Mn6O2} Core in Polymeric Structures
Crystals 2018, 8(2), 100; doi:10.3390/cryst8020100 -
Abstract
A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5),
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A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5), and [Mn6O2(O2CCMe3)10(HO2CCMe3)2(en)]n (6), have been synthesized (where pyz = pyrazine, en = ethyl nicotinate). The modification of the cluster surface by a diverse combination of capped or bridging ligands attached to peripheral MnII atoms results in discrete clusters with a closed hydrophobic exterior shell in 1 and 2, supramolecular chains built through hydrogen bonded solvent molecule clusters in 3, linear coordination polymers in 4 and 6 or a ladder-like coordination polymer in 5. The H-bonded coordination polymers 4 and 5 form supramolecular layers in crystals. Full article
Open AccessArticle
Atomic Charges and Chemical Bonding in Y-Ga Compounds
Crystals 2018, 8(2), 99; doi:10.3390/cryst8020099 -
Abstract
A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules
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A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules revealed an increase in the atomic volumes of both Y and Ga with the increase in yttrium content. The non-linear increase is caused by the strengthening of covalent Y-Ga interactions with stronger participation of genuine penultimate shell electrons (4d electrons of yttrium) in the valence region. Summing the calculated individual atomic volumes for a unit cell allows understanding of the experimental trend. With increasing yttrium content, the polarity of the Y-Ga bonding and, thus its ionicity, rises. The covalency of the atomic interactions in Y-Ga compounds is consistent with their delocalization from two-center to multi-center ones. Full article
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Open AccessArticle
The Electrical Properties of Tb-Doped CaF2 Nanoparticles under High Pressure
Crystals 2018, 8(2), 98; doi:10.3390/cryst8020098 -
Abstract
The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb
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The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb3+ leads to deformation in the lattice, and finally lowers the transition pressure. The F ions diffusion, electronic transport, and charge-discharge process become more difficult with the rising pressure. In the electronic transport process, defects at grains play a dominant role. The charge carriers include both F ions and electrons, and electrons are dominant in the transport process. The Tb doping improves the pressure effect on the transport behavior of CaF2 nanocrystals. Full article
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Open AccessArticle
Crystal Structure of Shigella flexneri SF173 Reveals a Dimeric Helical Bundle Conformation
Crystals 2018, 8(2), 97; doi:10.3390/cryst8020097 -
Abstract
We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping
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We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping the N-terminal α1 helix of each monomer. Structural inspection and genomic analysis results suggest that the SF173 might play its putative function by binding to SF172, the partially overlapped upstream product in the operon. As YaeO (an SF172 orthologue) has been identified to be an inhibitor of the bacterial transcription terminator Rho protein, SF173 is suggested to be involved in the regulation of Rho-dependent transcription termination, by inhibiting the Rho protein binding to SF172/YaeO. Full article
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Open AccessArticle
Ultra-Wide-Bandwidth Tunable Magnetic Fluid-Filled Hybrid Connected Dual-Core Photonic Crystal Fiber Mode Converter
Crystals 2018, 8(2), 95; doi:10.3390/cryst8020095 -
Abstract
We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to
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We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to convert LP11 in the index-guiding core to the LP01 mode in the photonic bandgap-guiding core. By introducing the magnetic fluid into the air-hole located at the center of the photonic bandgap-guiding core, the mode converter can realize a high coupling efficiency and an ultra-wide bandwidth. The coupling efficiency can reach up to 99.9%. At a fixed fiber length, by adjusting the strength of the magnetic field, the coupling efficiency can reach up to 90% and 95% at wavelengths in the ranges of 1.33 µm–1.85 µm and 1.38 µm–1.75 µm, with bandwidth values reaching 0.52 µm and 0.37 µm, respectively. Moreover, it has a good manufacturing flexibility. The mode converter can be used to implement wideband mode-division multiplexing of few-mode optical fiber for high-capacity telecommunications. Full article
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Open AccessArticle
Effects of Alloying Atoms on Antiphase Boundary Energy and Yield Stress Anomaly of L12 Intermetallics: First-Principles Study
Crystals 2018, 8(2), 96; doi:10.3390/cryst8020096 -
Abstract
The antiphase boundary energies of {111} and {010} planes in L12 intermetallics (Ni3Ge, Ni3Si, Al3Sc, Ni3Al, Ni3Ga and Al3Ti) under different pressure are presented using first-principle methods. The yield stress
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The antiphase boundary energies of {111} and {010} planes in L12 intermetallics (Ni3Ge, Ni3Si, Al3Sc, Ni3Al, Ni3Ga and Al3Ti) under different pressure are presented using first-principle methods. The yield stress anomaly is predicted by the energy criterion p-factor based on the anisotropy of antiphase boundary energies and elasticity. These L12 intermetallics exhibit anomalous yield stress behavior except Al3Sc. It is found that pressure cannot introduce the transition between anomalous and normal behavior. In order to investigate the transition, Al3Sc, Ni3Si and Ni3Ge with substituting atoms are investigated in detail due to p-factors of them are close to the critical value pc=3. Al3Sc can change to anomalous when Sc atoms in {010} planes are substituted by Ti with plane concentration 25%. When Li substitutes Al in {111} planes, anomalous Al3Sc will change to normal. Ni3Si and Ni3Ge can exhibit normal yield stress behavior when Ge and Si in {111} planes are substituted by alloying atoms with plane concentrations 12.5% and 25%. When Ga and Al substitute in {010} planes, normal Ni3Si and Ni3Ge will revert to anomalous behavior. Therefore, transparent transition between normal and anomalous yield stress behavior in L12 intermetallics can be introduced by alloying atoms. Full article
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Open AccessArticle
First-Principles Investigations of the Structural, Anisotropic Mechanical, Thermodynamic and Electronic Properties of the AlNi2Ti Compound
Crystals 2018, 8(2), 93; doi:10.3390/cryst8020093 -
Abstract
In this paper, the electronic, mechanical and thermodynamic properties of AlNi2Ti are studied by first-principles calculations in order to reveal the influence of AlNi2Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi2
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In this paper, the electronic, mechanical and thermodynamic properties of AlNi2Ti are studied by first-principles calculations in order to reveal the influence of AlNi2Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi2Ti has relatively high mechanical properties, which will benefit the impact or wear resistance of the ZTA/Fe composite. The values of bulk, shear and Young’s modulus are 164.2, 63.2 and 168.1 GPa respectively, and the hardness of AlNi2Ti (4.4 GPa) is comparable to common ferrous materials. The intrinsic ductile nature and strong metallic bonding character of AlNi2Ti are confirmed by B/G and Poisson’s ratio. AlNi2Ti shows isotropy bulk modulus and anisotropic elasticity in different crystallographic directions. At room temperature, the linear thermal expansion coefficient (LTEC) of AlNi2Ti estimated by quasi-harmonic approximation (QHA) based on Debye model is 10.6 × 10−6 K−1, close to LTECs of zirconia toughened alumina and iron. Therefore, the thermal matching of ZTA/Fe composite with AlNi2Ti interfacial phase can be improved. Other thermodynamic properties including Debye temperature, sound velocity, thermal conductivity and heat capacity, as well as electronic properties, are also calculated. Full article
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Open AccessArticle
Mg2FeH6 Synthesis Efficiency Map
Crystals 2018, 8(2), 94; doi:10.3390/cryst8020094 -
Abstract
The influences of the processing parameters on the Mg2FeH6 synthesis yield were studied. Mixtures of magnesium hydride (MgH2) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods
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The influences of the processing parameters on the Mg2FeH6 synthesis yield were studied. Mixtures of magnesium hydride (MgH2) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods and subsequently sintered at temperatures from 300–500 C under hydrogen. The reaction yield, phase content and hydrogen storage properties of the received materials were investigated. The morphologies of the powders after synthesis were studied by SEM. The synthesis effectiveness map was presented. The obtained results prove that synthesis parameters, such as the milling time and synthesis temperature, greatly influence the reaction yield and material properties and show that extended mechanical milling may not be beneficial to the reaction efficiency. Full article
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Open AccessArticle
Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures
Crystals 2018, 8(2), 90; doi:10.3390/cryst8020090 -
Abstract
The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH
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The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH2, Ni has been added to form Mg2NiH4, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg2NiH4-LiBH4-M(BH4)x (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 °C up to 216 °C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg2NiH4 but only slight differences have been detected by changing the borohydrides in the eutectic mixture. Full article
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Open AccessArticle
Temperature-Induced Reversible and Irreversible Transitions between Metastable Perovskite Phases in the BiFe1−yScyO3 Solid Solutions
Crystals 2018, 8(2), 91; doi:10.3390/cryst8020091 -
Abstract
The antipolar orthorhombic Pnma phase with the 2ap×4ap×22ap superstructure (ap ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO3. Temperature-induced
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The antipolar orthorhombic Pnma phase with the 2ap×4ap×22ap superstructure (ap ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO3. Temperature-induced structural transformations in metastable perovskite solid solutions with the Pnma structure corresponding to the range of 0.30 ≤ y ≤ 0.60 of the (1−y)BiFeO3-yBiScO3 quasi binary system were studied using temperature X-ray and neutron powder diffraction. These compositions cannot be prepared in bulk form at ambient pressure but can be stabilized in the Pnma phase by means of quenching after synthesis under high pressure. The compositions were investigated in situ between 1.5 K and the temperature of the stability limit of their metastable phases (about 870–920 K). It has been found that heating the as-prepared compositions with the Pnma phase leads to formation of the rhombohedral R3c phase (2ap×2ap×23ap), which, on cooling down to room temperature, either remains or transforms into a polar orthorhombic Ima2 phase (2ap×2ap×2ap). The observed phase transformations in the BiFe1−yScyO3 perovskite series on heating and on cooling are considered in terms of geometrical factors. Full article
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Open AccessArticle
Specific Structural Disorder in an Anion Layer and Its Influence on Conducting Properties of New Crystals of the (BEDT-TTF)4A+[M3+(ox)3]G Family, Where G Is 2-Halopyridine; M Is Cr, Ga; A+ Is [K0.8(H3O)0.2]+
Crystals 2018, 8(2), 92; doi:10.3390/cryst8020092 -
Abstract
New crystals (14) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G
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New crystals (14) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G is 2-chloropyridine, 2-bromopyridine; and A+ is [K0.8(H3O)0.2]+ have been prepared and their crystal structure and transport properties were studied. All crystals belong to the monoclinic group of the (BEDT-TTF)4A+[M3+(ox)3]G family with β″-packing type of conducting BEDT-TTF layers. In contrast to the known superconducting crystals with M3+ = Fe3+ and G = 2-chloro- or 2-bromopyridine (Tc = 4.0–4.3 K), crystals with Cr3+ and Ga3+ ions exhibit metallic properties down to 0.5 K without superconducting transition. Upon cooling these crystals, the incommensurate superstructure appears, which has never been observed before in the numerous β″-salts of the family. In addition, orthorhombic (sp. group Pbca) semiconducting crystals α″-(BEDT-TTF)5[Ga(ox)3]·3.4·H2O·0.6 EtOH (5) were obtained. It is a new compound in the family of BEDT-TTF crystals with tris(oxalato)metallate anions. Full article
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Open AccessArticle
Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction
Crystals 2018, 8(2), 89; doi:10.3390/cryst8020089 -
Abstract
Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4] or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions
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Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4] or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH4. In cases wherein alkaline-earth metals (M) are used as a metal cation, MAlH5 with corner-sharing AlH6 octahedron chains are known to form. The crystal structure of SrAlH5 has remained unsolved although two different results have been theoretically and experimentally proposed. Focusing on the corner-sharing AlH6 octahedron chains as a unique feature of the alkaline-earth metal, we here report the crystal structure of SrAlD5 investigated by synchrotron radiation powder X-ray and neutron diffraction. SrAlD5 was elucidated to adopt an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4. The Al–D distances (1.77–1.81 Å) in the corner-sharing AlD6 octahedra matched with those in the isolated [AlD6]3− although the D–Al–D angles in the penta-alanates are significantly more distorted than the isolated [AlD6]3−. Full article
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Open AccessArticle
A Standard Structure for Bile Acids and Derivatives
Crystals 2018, 8(2), 86; doi:10.3390/cryst8020086 -
Abstract
The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are
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The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are described. Average bond lengths and bond angles from the crystal structures of 26 monomers and four dimers (some of them in several solvents) of bile acids and esters (and derivatives) are used for proposing a standard steroid nucleus. The hydrogen bond network and conformation of the lateral chain are also discussed. This standard structure was used to compare with the structures of both progesterone and cholesterol. Full article
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Open AccessArticle
Low-Temperature Lattice Effects in the Spin-Liquid Candidate κ-(BEDT-TTF)2Cu2(CN)3
Crystals 2018, 8(2), 87; doi:10.3390/cryst8020087 -
Abstract
The quasi-two-dimensional organic charge-transfer salt κ-(BEDT-TTF)2Cu2(CN)3 is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive
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The quasi-two-dimensional organic charge-transfer salt κ-(BEDT-TTF)2Cu2(CN)3 is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive investigations of the material’s low-temperature properties, several important questions remain to be answered. Particularly puzzling are the 6 K anomaly and the enigmatic effects observed in magnetic fields. Here we report on low-temperature measurements of lattice effects which were shown to be particularly strongly pronounced in this material (R. S. Manna et al., Phys. Rev. Lett.2010, 104, 016403)). A special focus of our study lies on sample-to-sample variations of these effects and their implications on the interpretation of experimental data. By investigating overall nine single crystals from two different batches, we can state that there are considerable differences in the size of the second-order phase transition anomaly around 6 K, varying within a factor of 3. In addition, we find field-induced anomalies giving rise to pronounced features in the sample length for two out of these nine crystals for temperatures T< 9 K. We tentatively assign the latter effects to B-induced magnetic clusters suspected to nucleate around crystal imperfections. These B-induced effects are absent for the crystals where the 6 K anomaly is most strongly pronounced. The large lattice effects observed at 6 K are consistent with proposed pairing instabilities of fermionic excitations breaking the lattice symmetry. The strong sample-to-sample variation in the size of the phase transition anomaly suggests that the conversion of the fermions to bosons at the instability is only partial and to some extent influenced by not yet identified sample-specific parameters. Full article
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Open AccessArticle
Coupling between Spin and Charge Order Driven by Magnetic Field in Triangular Ising System LuFe2O4+δ
Crystals 2018, 8(2), 88; doi:10.3390/cryst8020088 -
Abstract
We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel
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We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (TN = 240 K) indicates that LuFe2O4+δ shows short-range, two-dimensional (2D) correlations in the FeO5 triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K. We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k1 = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D) spin correlation between the FeO5 bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k2 = (1/3, 1/3, 3/2). This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k1 component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field. Full article
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Open AccessArticle
Febuxostat-Minoxidil Salt Solvates: Crystal Structures, Characterization, Interconversion and Solubility Performance
Crystals 2018, 8(2), 85; doi:10.3390/cryst8020085 -
Abstract
Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (1H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These
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Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (1H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These febuxostat-minoxidil salt solvates feature isostructural with the same stoichiometries (1:1:1 molecule ratio). The proton transfers from the carboxylic group of febuxostat (FEB) to imino N atom of minoxidil (MIN), which forms the motif with combined R22(9) R42(8) R22(9) graph set in the three solvates. The solvents occupy the different positions related to the motif, which results in the apparent differences in PXRD patterns before/after desolvation although they are isostructures. The FEB-MIN·THF was more thermostable than FEB-MIN·ACE and FEB-MIN·IPA relative to solvent removal from DSC patterns, which is different from the results from the solvent-exchange experiments in chemical kinetics. All three salt solvates exhibit increased equilibrium solubility compared to FEB in aqueous medium. Full article
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Open AccessArticle
The Carbonate Platform Model and Reservoirs’ Origins of the Callovian-Oxfordian Stage in the Amu Darya Basin, Turkmenistan
Crystals 2018, 8(2), 84; doi:10.3390/cryst8020084 -
Abstract
The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard
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The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard facies belts and some microfacies types were recognized, and sedimentary model “carbonate ramp-rimmed platform” was proposed and established that can be compared with the classical carbonate sedimentary models. In this model, favorable reservoirs not only developed in the intraplatform shoal of open platform, or reef and shoal on the platform margin, but also in the patch reefs, shoal and mound facies on the upper slope. The reservoir’s pore space is dominated by intergranular and intragranular pores and fissure-pore reservoirs exist with medium porosity and medium to low permeability. Sedimentary facies and diagenetic dissolution are the key controlling factors for the development of high-quality reservoirs. Full article
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