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Crystals, Volume 2, Issue 2 (June 2012) – 34 articles , Pages 159-729

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1170 KiB  
Article
Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range
by Yevheniy Pivak, Herman Schreuders and Bernard Dam
Crystals 2012, 2(2), 710-729; https://doi.org/10.3390/cryst2020710 - 20 Jun 2012
Cited by 21 | Viewed by 7450
Abstract
Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆Hdes = −78.3 kJ/molH2, [...] Read more.
Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆Hdes = −78.3 kJ/molH2, Sdes = −136.1 J/K molH2, estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, ∆Habs = −61.6 kJ/molH2, ∆Sabs = −110.9 J/K molH2, appear to be substantially affected by the clamping of the film to the substrate. The clamping is negligible at high temperatures, T > 523 K, while at lower temperatures, T < 393 K, it is considerable. The hysteresis at room temperature in Mg/Ta/Pd films increases by a factor of 16 as compared to MgH2 bulk. The hysteresis increases even further in Mg/Pd films, most likely due to the formation of a Mg-Pd alloy at the Mg/Pd interface. The stress–strain analysis of the Mg/Ta/Pd films at 300–333 K proves that the increase of the hysteresis occurs due to additional mechanical work during the (de-)hydrogenation cycle. With a proper temperature correction, our stress–strain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range. Full article
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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807 KiB  
Article
Ru11Lu20, a New Intermetallic Compound with Eight- to Ten-Coordinate Ruthenium Atoms
by Sina Zimmermann, Ingo Pantenburg and Gerd Meyer
Crystals 2012, 2(2), 704-709; https://doi.org/10.3390/cryst2020704 - 20 Jun 2012
Cited by 5 | Viewed by 5487
Abstract
The new intermetallic compound Ru11Lu20 was obtained as black single crystals during an attempted comproportionation reaction of lutetium(III) chloride, LuCl3, with metallic lutetium in the presence of ruthenium metal at 950 °C. Ru11Lu20 crystallizes with [...] Read more.
The new intermetallic compound Ru11Lu20 was obtained as black single crystals during an attempted comproportionation reaction of lutetium(III) chloride, LuCl3, with metallic lutetium in the presence of ruthenium metal at 950 °C. Ru11Lu20 crystallizes with the trigonal space group R-3, Z = 6, a = 1255.1(1), c = 2973.0(4) pm, R1 for all data: 0.0380. Ruthenium atoms center eight-, nine- and ten-vertex polyhedra of lutetium atoms which are connected in a complicated manner to a three-dimensional network. Full article
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1679 KiB  
Article
Silica-Metal Composite for Hydrogen Storage Applications
by Marzia Pentimalli, Enrico Imperi, Mariangela Bellusci, Carlo Alvani, Andrea Santini and Franco Padella
Crystals 2012, 2(2), 690-703; https://doi.org/10.3390/cryst2020690 - 18 Jun 2012
Cited by 7 | Viewed by 6388
Abstract
In spite of their favourable chemical characteristics, using AB5 alloys as fixed bed for hydrogen storage devices requires proper management of a number of technological aspects. Among these, the mechanical stability of metal particle grains under hydrogen cycling and the overall thermal conductivity [...] Read more.
In spite of their favourable chemical characteristics, using AB5 alloys as fixed bed for hydrogen storage devices requires proper management of a number of technological aspects. Among these, the mechanical stability of metal particle grains under hydrogen cycling and the overall thermal conductivity of the material bed constitute crucial features. We developed by High Energy Ball Milling HEBM a mechanically stable silica-based AB5 composite with enhanced thermal conductivity. Here, focusing on the material’s physical-chemical properties, we report on the silica-AB5 composite development and characterization. Particularly, we studied the material consolidation process, the resulting composite morphology and the system behaviour under hydrogen loading/unloading cycling. Full article
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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889 KiB  
Article
Inorganic Amino-Nitro-Guanidinium Derivatives
by Niko Fischer, Thomas M. Klapötke, Karin Lux, Franz A. Martin and Jörg Stierstorfer
Crystals 2012, 2(2), 675-689; https://doi.org/10.3390/cryst2020675 - 18 Jun 2012
Cited by 7 | Viewed by 6854
Abstract
1-Amino-3-nitroguanidine (ANQ, 1) was synthesized by hydrazinolysis of nitroguanidine (NQ) with hydrazine hydrate. Four different amino-nitroguanidinium salts (chloride (2), bromide (3), iodide (4) and sulfate (5)) were synthesized and structurally characterized by low-temperature X-ray [...] Read more.
1-Amino-3-nitroguanidine (ANQ, 1) was synthesized by hydrazinolysis of nitroguanidine (NQ) with hydrazine hydrate. Four different amino-nitroguanidinium salts (chloride (2), bromide (3), iodide (4) and sulfate (5)) were synthesized and structurally characterized by low-temperature X-ray diffraction. The halides 24 could only be obtained crystalline as monohydrates. In addition, they were characterized by NMR and vibrational spectroscopy, elemental analysis and the sensitivities towards impact, friction and electrostatic discharge were determined. The compounds can be used in silver (AgX, X = Cl, Br, I) and barium (BaSO4) based metathesis reactions in order to form more complex salts of 1-amino-nitroguanidine. Full article
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338 KiB  
Communication
Non-Covalent Interactions in the Crystal Structure of Methyl 4-Hydroxy-3-Nitrobenzoate
by Xin-Ling Fu, Jiang-Sheng Li and Jim Simpson
Crystals 2012, 2(2), 669-674; https://doi.org/10.3390/cryst2020669 - 12 Jun 2012
Cited by 3 | Viewed by 6034
Abstract
Methyl 4-hydroxy-3-nitrobenzoate, (I), C8H7NO5, crystallizes with two unique molecules, A and B, in the asymmetric unit of the triclinic unit cell. The space group was assigned as P-1, with lattice parameters a = 0.72831(15), b = 1.0522(2), [...] Read more.
Methyl 4-hydroxy-3-nitrobenzoate, (I), C8H7NO5, crystallizes with two unique molecules, A and B, in the asymmetric unit of the triclinic unit cell. The space group was assigned as P-1, with lattice parameters a = 0.72831(15), b = 1.0522(2), c = 1.1410(2) nm, α = 83.38(3), β = 80.83(3), γ = 82.02(3)°, Z = 4, V = 0.8510(3) nm3, Mr = 197.15, Dc = 1.539 g/m3, µ= 0.131 mm−1, F(000) = 408, R = 0.1002 and wR = 0.2519. In the crystal structure, 12 hydrogen bonding and two p-stacking interactions link the molecules into infinite stacked sheets parallel to (101). Full article
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329 KiB  
Article
Single-Component Charge-Transfer Crystals Based on Spin-Carrying TCNQ (7,7,8,8-Tetracyanoquinodimethane) Derivatives
by Hideto Suzuki, Hiroki Akutsu, Jun-ichi Yamada and Shin’ichi Nakatsuji
Crystals 2012, 2(2), 662-668; https://doi.org/10.3390/cryst2020662 - 12 Jun 2012
Cited by 3 | Viewed by 5861
Abstract
Three TCNQ derivatives carrying nitroxide radicals (3a3c) were prepared and were found to form single-component charge-transfer (CT) complexes by self-assembly, in which outer nitroxide groups of a couple of different molecules work as donors and the inner TCNQ unit [...] Read more.
Three TCNQ derivatives carrying nitroxide radicals (3a3c) were prepared and were found to form single-component charge-transfer (CT) complexes by self-assembly, in which outer nitroxide groups of a couple of different molecules work as donors and the inner TCNQ unit of another molecule as an acceptor. While the CT interactions found for the TEMPO (2,2,6,6-tetramethylpiperidin-1-oxy) derivative 3a and the PROXYL (2,2,5,5-tetramethylpirrolidin-1-oxy) derivative 3b are point-to-face fashion between the oxygen atom of each nitroxide group and the six-membered ring of inner TCNQ unit, the CT interactions found for the PO (2,2,5,5-tetramethyl-3-pyrrolin-1-oxy) derivative 3c are point-to-point contacts between the oxygen atoms of outer nitroxide groups and the carbon atoms of a couple of cyano groups. Full article
(This article belongs to the Special Issue Molecular Conductors)
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3580 KiB  
Review
Transport Phenomena in Multilayered Massless Dirac Fermion System α-(BEDT-TTF)2I3
by Naoya Tajima, Yutaka Nishio and Koji Kajita
Crystals 2012, 2(2), 643-661; https://doi.org/10.3390/cryst2020643 - 11 Jun 2012
Cited by 7 | Viewed by 6924
Abstract
A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to [...] Read more.
A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermion system with anisotropic Fermi velocity. This system exhibits remarkable transport phenomena characteristic to electrons on the Dirac cone type energy structure. Full article
(This article belongs to the Special Issue Molecular Conductors)
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1345 KiB  
Article
Single-Crystal-to-Single-Crystal Transformation from δ-(BEDT-TTF)4[OsNOCl5]1.33(C6H5NO2)0.67 to β"-(BEDT-TTF)3[OsNOCl5]
by Leokadiya Zorina, Sergey Simonov, Enric Canadell and Rimma Shibaeva
Crystals 2012, 2(2), 627-642; https://doi.org/10.3390/cryst2020627 - 07 Jun 2012
Cited by 1 | Viewed by 6600
Abstract
We report on the single-crystal-to-single-crystal transformation occurring over time in a layered organic molecular conductor based on BEDT-TTF. The process is connected with removal of solvent molecules from the complex anion layer resulting in concomitant partial irreversible conversion of the δ-(BEDT-TTF)4[OsNOCl [...] Read more.
We report on the single-crystal-to-single-crystal transformation occurring over time in a layered organic molecular conductor based on BEDT-TTF. The process is connected with removal of solvent molecules from the complex anion layer resulting in concomitant partial irreversible conversion of the δ-(BEDT-TTF)4[OsNOCl5]1.33(C6H5NO2)0.67 structure to the β"-(BEDT-TTF)3[OsNOCl5] structure. Along with symmetry lowering from I2/a to Р, huge, drastic changes in the conducting BEDT-TTF layer as well as in the anion arrangement are observed, meanwhile crystallinity of the sample is retained. Coexistence of two phases, parent δ and daughter β" in the same crystal helps in the study of their mutual orientation as well as to formulate a mechanism for the structural transformation. Full article
(This article belongs to the Special Issue Molecular Conductors)
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789 KiB  
Article
Growth Mechanisms of CdS Nanocrystals in Aqueous Media
by Loredana Latterini and Alessandro Iagatti
Crystals 2012, 2(2), 618-626; https://doi.org/10.3390/cryst2020618 - 06 Jun 2012
Cited by 2 | Viewed by 5656
Abstract
CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared [...] Read more.
CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared using water-in-heptane or water-in-nonane microemulsions. The results obtained from the investigation of nanocrystals prepared using heptane as the organic phase, confirmed that nanocrystal nucleation is fast while their growth is determined by droplet exchange content rate. Size distribution histograms obtained from the sample at early time points after mixing presented a bimodal population having average sizes of 3.0 ± 0.1 and 5.8 ± 0.1 nm, thus indicating that surface process controls the nanocrystal growth. With longer reaction times the occurrence of water droplet coalescence is likely responsible for the formation of nanocrystal agglomerates. Using a water-in-nonane microemulsion, the droplet exchange rate can be modified, thus leading to smaller CdS nanocrystals. However, the development of structural defects cannot be excluded, as evidenced by the luminescence spectra of the suspension. In general, aging of the nanocrystal in the pristine microemulsion resulted in the development of cubic semiconductor nanostructures. Full article
(This article belongs to the Special Issue Semiconductor Nanocrystals)
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2202 KiB  
Review
Photoinduced Phase Transitions in α-, θ-, and κ-type ET Salts: Ultrafast Melting of the Electronic Ordering
by Shinichiro Iwai
Crystals 2012, 2(2), 590-617; https://doi.org/10.3390/cryst2020590 - 30 May 2012
Cited by 10 | Viewed by 8116
Abstract
Photoinduced phase transitions in organic compounds with strong electron correlation ET [bis(ethylenedithio)-tetrathiafulvalene)-based salts α-(ET)2I3, θ-(ET)2RbZn(SCN)4, κ-(d-ET)2Cu[N(CN)2Br] were discussed based, on time resolved optical pump-probe spectroscopy using ~150 fs mid-infrared [...] Read more.
Photoinduced phase transitions in organic compounds with strong electron correlation ET [bis(ethylenedithio)-tetrathiafulvalene)-based salts α-(ET)2I3, θ-(ET)2RbZn(SCN)4, κ-(d-ET)2Cu[N(CN)2Br] were discussed based, on time resolved optical pump-probe spectroscopy using ~150 fs mid-infrared pulse, 12 fs near infrared pulse, and sub-picosecond terahertz pulse. (i) In charge-ordered insulators α-(ET)2I3 and θ-(ET)2RbZn(SCN)4, we captured ultrafast snapshots of charge dynamics i.e., immediate (ca. 15 fs) generation of a microscopic metallic state (or equivalently the microscopic melting of the charge order) which is driven by the coherent oscillation (period; 18 fs) of correlated electrons. Subsequently, condensation of the microscopic metallic state to the macroscopic scale occurs in α-(ET)2I3. However, in θ-(ET)2RbZn(SCN)4, such condensation is prevented by the large potential barrier reflecting the structural difference between the insulator and metal; (ii) In a Dimer–Mott insulator κ-(d-ET)2Cu[N(CN)2Br], photogeneration of the metallic state rises during ca. 1 ps that is much slower than the melting of charge order, because the photoinduced insulator to metal transition is driven by the intradimer molecular displacement in the dimer Mott insulator. The ultrafast dynamics of photoinduced insulator–metal transitions depend strongly on the molecular arrangement, reflecting various competing phases in the ET sheets. Full article
(This article belongs to the Special Issue Molecular Conductors)
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863 KiB  
Article
Spin and Charge Transport in the X-ray Irradiated Quasi-2D Layered Compound: κ-(BEDT-TTF)2Cu[N(CN)2]Cl
by Ágnes Antal, Titusz Fehér, Naoki Yoneyama, László Forró, Takahiko Sasaki and András Jánossy
Crystals 2012, 2(2), 579-589; https://doi.org/10.3390/cryst2020579 - 24 May 2012
Cited by 3 | Viewed by 5634
Abstract
The interplane spin cross relaxation time Tx measured by high frequency ESR in X-ray irradiated κ-(BEDT-TTF)2Cu[N(CN)2]Cl is compared to the interplane resisitivity ρ⊥and the in-plane resistivity ρII between 50 K and 250 K. The irradiation [...] Read more.
The interplane spin cross relaxation time Tx measured by high frequency ESR in X-ray irradiated κ-(BEDT-TTF)2Cu[N(CN)2]Cl is compared to the interplane resisitivity ρ⊥and the in-plane resistivity ρII between 50 K and 250 K. The irradiation transforms the semiconductor behavior of the non-irradiated crystal into metallic. Irradiation decreases Tx, ρ⊥ and ρII but the ratio Tx/ρ⊥ and ρ⊥/ρII remain unchanged between 50 and 250 K. Models describing the unusual defect concentration dependence in κ-(BEDT-TTF)2Cu[N(CN)2]Cl are discussed. Full article
(This article belongs to the Special Issue Molecular Conductors)
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11048 KiB  
Article
Comprehensive Optical Investigations of Charge Order in Organic Chain Compounds (TMTTF)2X
by Martin Dressel, Michael Dumm, Tobias Knoblauch and Matteo Masino
Crystals 2012, 2(2), 528-578; https://doi.org/10.3390/cryst2020528 - 23 May 2012
Cited by 63 | Viewed by 9684
Abstract
Charge ordering in the (TMTTF)2X salts with centrosymmetric anions (X = PF‾6 , AsF‾6 , SbF‾6 ) leads to a ferroelectric state around 100 K. For the first time and in great completeness, the intra- and intermolecular vibrational [...] Read more.
Charge ordering in the (TMTTF)2X salts with centrosymmetric anions (X = PF‾6 , AsF‾6 , SbF‾6 ) leads to a ferroelectric state around 100 K. For the first time and in great completeness, the intra- and intermolecular vibrational modes of (TMTTF)2X have been investigated by infrared and Raman spectroscopy as a function of temperature and pressure for different polarizations. In this original paper, we explore the development and amount of charge disproportionation and the coupling of the electronic degrees of freedom to the counterions and the underlying lattice. The methyl groups undergo changes with temperature that are crucial for the anion cage formed by them. We find that the coupling of the TMTTF molecules to the hexafluorine anions changes upon cooling and especially at the charge-order transition, indicating a distortion of the anion. Additional features are identified that are caused by the anharmonic potential. The spin-Peierls transition entails additional modifications in the charge distribution. To complete the discussion, we also add the vibrational frequencies and eigenvectors based on ab-initio quantum-chemical calculations. Full article
(This article belongs to the Special Issue Molecular Conductors)
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230 KiB  
Communication
Ethyl 2,6-Dimethoxybenzoate: Synthesis, Spectroscopic and X-ray Crystallographic Analysis
by Imtiaz Khan, Aliya Ibrar and Jonathan M. White
Crystals 2012, 2(2), 521-527; https://doi.org/10.3390/cryst2020521 - 22 May 2012
Cited by 8 | Viewed by 5970
Abstract
The acid catalyzed esterification of 2,6-dimethoxybenzoic acid (1) in the presence of absolute ethanol afforded ethyl 2, 6-dimethoxybenzoate (2). The structure of the resulting compound was supported by spectroscopic data and unambiguously confirmed by single crystal X-ray diffraction studies. [...] Read more.
The acid catalyzed esterification of 2,6-dimethoxybenzoic acid (1) in the presence of absolute ethanol afforded ethyl 2, 6-dimethoxybenzoate (2). The structure of the resulting compound was supported by spectroscopic data and unambiguously confirmed by single crystal X-ray diffraction studies. The title compound crystallized in the triclinic space group P ī with unit cell parameters a = 8.5518(3) Å, b = 10.8826(8) Å, c = 11.9939(6) Å, α = 101.273(5)°, β = 98.287(3)°, γ = 94.092(4)°, V = 1077.54(10) Å3, Z = 4, Dc = 1.296 Mg/m3, F(000) = 448 and μ = 0.098 mm−1. Compound (2) crystallizes with two molecules in the asymmetric unit with similar conformations. Full article
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973 KiB  
Review
Structural Aspects of the Bechgaard and Fabre Salts: An Update
by Jean-Paul Pouget
Crystals 2012, 2(2), 466-520; https://doi.org/10.3390/cryst2020466 - 21 May 2012
Cited by 52 | Viewed by 7808
Abstract
We review structural aspects of the Bechgaard and Fabre salts in relationship with their electronic, magnetic and superconducting properties. We emphasize the role of bond and charge modulations of the quarter filled organic stack in the various instabilities and ground states exhibited by [...] Read more.
We review structural aspects of the Bechgaard and Fabre salts in relationship with their electronic, magnetic and superconducting properties. We emphasize the role of bond and charge modulations of the quarter filled organic stack in the various instabilities and ground states exhibited by these salts. A special consideration is also devoted to the influence of anions and methyl groups in these processes. In particular we point out the importance of the anions in achieving the inter-stack coupling by either direct or indirect (via the polarization of the methyl group cavities) interactions with the donors. In this framework we discuss the role of anions and methyl group disorders in the inhibition of the divergence of the high temperature bond order wave instability of the Bechgaard salts. We analyze the modulation in the magnetic ground states by considering explicitly the coupling of the magnetization with structural degrees of freedom. We consider the role of the anions and methyl groups in stabilizing the charge ordering pattern in the Fabre salts. We also discuss the spin-Peierls transition of the Fabre salts in relation with the charge ordering transition and the adiabaticity of the phonon field. We review the anion ordering transitions by considering more particularly the influence of the ordering process on the electronic structure and on the ground states which results. In this framework we show that the texture of the anion ordered structure has direct consequences on the superconducting properties of (TMTSF)2ClO4. Finally we conclude on the essential implication of the structural degrees of freedom on the generic phase diagram of the Bechgaard and Fabre salts. Full article
(This article belongs to the Special Issue Molecular Conductors)
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1001 KiB  
Article
Synthesis, Structure and Solid State Properties of Cyclohexanemethylamine Substituted Phenalenyl Based Molecular Conductor
by Pradip Bag, Mikhail E. Itkis, Sushanta K. Pal, Elena Bekyarova, Bruno Donnadieu and Robert C. Haddon
Crystals 2012, 2(2), 446-465; https://doi.org/10.3390/cryst2020446 - 14 May 2012
Cited by 4 | Viewed by 7122
Abstract
We report the preparation, crystallization and solid state characterization of a cyclohexanemethylamine substituted spirobiphenalenyl radical; in the solid state the compound is iso-structural with its dehydro-analog (benzylamine-substitued compound), and the molecules packed in a one-dimensional fashion that we refer to as a π-step [...] Read more.
We report the preparation, crystallization and solid state characterization of a cyclohexanemethylamine substituted spirobiphenalenyl radical; in the solid state the compound is iso-structural with its dehydro-analog (benzylamine-substitued compound), and the molecules packed in a one-dimensional fashion that we refer to as a π-step stack. Neighboring molecules in the stack interact via the overlap of one pair of active (spin bearing) carbon atoms per phenalenyl unit. The magnetic susceptibility measurement indicates that in the solid state the radical remains paramagnetic and the fraction of Curie spins is 0.75 per molecule. We use the analytical form of the Bonner-Fisher model for the S = 1/2 antiferromagnetic Heisenberg chain of isotropically interacting spins with intrachain spin coupling constant J = 6.3 cm−1, to fit the experimentally observed paramagnetism [χp (T)] in the temperature range 4–330 K. The measured room temperature conductivity (σRT = 2.4 × 10–3 S/cm) is comparable with that of the iso-structural benzyl radical, even though the calculated band dispersions are smaller than that of the unsaturated analog. Full article
(This article belongs to the Special Issue Molecular Conductors)
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1437 KiB  
Review
Moderate Temperature Dense Phase Hydrogen Storage Materials within the US Department of Energy (DOE) H2 Storage Program: Trends toward Future Development
by Scott McWhorter, Kathleen O’Malley, Jesse Adams, Grace Ordaz, Katie Randolph and Ned T. Stetson
Crystals 2012, 2(2), 413-445; https://doi.org/10.3390/cryst2020413 - 10 May 2012
Cited by 12 | Viewed by 11390
Abstract
Hydrogen has many positive attributes that make it a viable choice to augment the current portfolio of combustion-based fuels, especially when considering reducing pollution and greenhouse gas (GHG) emissions. However, conventional methods of storing H2 via high-pressure or liquid H2 do [...] Read more.
Hydrogen has many positive attributes that make it a viable choice to augment the current portfolio of combustion-based fuels, especially when considering reducing pollution and greenhouse gas (GHG) emissions. However, conventional methods of storing H2 via high-pressure or liquid H2 do not provide long-term economic solutions for many applications, especially emerging applications such as man-portable or stationary power. Hydrogen storage in materials has the potential to meet the performance and cost demands, however, further developments are needed to address the thermodynamics and kinetics of H2 uptake and release. Therefore, the US Department of Energy (DOE) initiated three Centers of Excellence focused on developing H2 storage materials that could meet the stringent performance requirements for on-board vehicular applications. In this review, we have summarized the developments that occurred as a result of the efforts of the Metal Hydride and Chemical Hydrogen Storage Centers of Excellence on materials that bind hydrogen through ionic and covalent linkages and thus could provide moderate temperature, dense phase H2 storage options for a wide range of emerging Proton Exchange Membrane Fuel Cell (PEM FC) applications. Full article
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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2775 KiB  
Article
Synthesis and Properties of 2-Alkylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene Derivatives and Crystal Structures of Their Cation Radical Salts
by Keisuke Furuta, Shuhei Kohno, Takashi Shirahata, Koya Yamasaki, Shojun Hino and Yohji Misaki
Crystals 2012, 2(2), 393-412; https://doi.org/10.3390/cryst2020393 - 09 May 2012
Cited by 4 | Viewed by 5998
Abstract
Tetrathiafulvalene derivatives condensed with 2-alkylidene-1,3-dithiole moiety, MeDTES (2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), EtDTES (2-(pentan-3-ylidene)-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), and CPDTES (2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene) have been synthesized. Crystal structure analysis of MeDTES salts with Au(CN)4, ReO4, and I3 and a [...] Read more.
Tetrathiafulvalene derivatives condensed with 2-alkylidene-1,3-dithiole moiety, MeDTES (2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), EtDTES (2-(pentan-3-ylidene)-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), and CPDTES (2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene) have been synthesized. Crystal structure analysis of MeDTES salts with Au(CN)4, ReO4, and I3 and a CPDTES salt with I3 reveals that the donor−anion ratios of all salts are 1:1. Band calculation of (MeDTES)[Au(CN)4] suggests a quasi-one-dimensional Fermi surface that could be the result of the uniform stack of donor molecules. In spite of this stacking, the salt is a Mott insulator because of a large on-site Coulomb interaction U. (MeDTES)(ReO4)(H2O)0.5 possesses Fermi points and exhibits semiconducting behavior with small activation energy (Ea = 0.058 eV). I3 ions form disordered infinite chain in (MeDTES)(I3)(DCE)0.25, but those in (CPDTES)(I3) exist as discrete ions. They show low conductivity (10−4−10−2 S cm−1) at room temperature and the band calculation suggests that they are band insulator. Full article
(This article belongs to the Special Issue Molecular Conductors)
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867 KiB  
Review
Mott-Anderson Transition in Molecular Conductors: Influence of Randomness on Strongly Correlated Electrons in the κ-(BEDT-TTF)2X System
by Takahiko Sasaki
Crystals 2012, 2(2), 374-392; https://doi.org/10.3390/cryst2020374 - 08 May 2012
Cited by 37 | Viewed by 10616
Abstract
The Mott-Anderson transition has been known as a metal-insulator (MI) transition due to both strong electron-electron interaction and randomness of the electrons. For example, the MI transition in doped semiconductors and transition metal oxides has been investigated up to now as a typical [...] Read more.
The Mott-Anderson transition has been known as a metal-insulator (MI) transition due to both strong electron-electron interaction and randomness of the electrons. For example, the MI transition in doped semiconductors and transition metal oxides has been investigated up to now as a typical example of the Mott-Anderson transition for changing electron correlations by carrier number control in concurrence with inevitable randomness. On the other hand, molecular conductors have been known as typical strongly correlated electron systems with bandwidth controlled Mott transition. In this paper, we demonstrate our recent studies on the randomness effect of the strongly correlated electrons of the BEDT-TTF molecule based organic conductors. X-ray irradiation on the crystals introduces molecular defects in the insulating anion layer, which cause random potential modulation of the correlated electrons in the conductive BEDT-TTF layer. In combination with hydrostatic pressure, we are able to control the parameters for randomness and correlations for electrons approaching the Mott-Anderson transition. Full article
(This article belongs to the Special Issue Molecular Conductors)
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391 KiB  
Article
Polyoxotungstate-Surfactant Layered Crystal toward Conductive Inorganic-Organic Hybrid
by Takeru Ito, Nozomu Fujimoto, Sayaka Uchida, Jun Iijima, Haruo Naruke and Noritaka Mizuno
Crystals 2012, 2(2), 362-373; https://doi.org/10.3390/cryst2020362 - 03 May 2012
Cited by 15 | Viewed by 6962
Abstract
A polyoxotungstate-surfactant hybrid layered compound was synthesized as a single phase by using decatungstate ([W10O32]4−, W10) and hexadecylpyridinium (C16py). The X-ray structure analysis combined with infrared spectroscopy and elemental analysis revealed the formula [...] Read more.
A polyoxotungstate-surfactant hybrid layered compound was synthesized as a single phase by using decatungstate ([W10O32]4−, W10) and hexadecylpyridinium (C16py). The X-ray structure analysis combined with infrared spectroscopy and elemental analysis revealed the formula to be (C16py)4[W10O32] (C16py-W10). The layered structure consisted of alternative stacking of W10 inorganic monolayers and interdigitated C16py bilayers with layered periodicity of 23.3 Å. Each W10 anion in the W10 inorganic monolayers was isolated by the hydrophilic heads of C16py. The hybrid crystals of C16py-W10 decomposed at around 500 K. The conductivity of the hybrid layered crystal was estimated to be 4.8 × 10−6 S cm−1 at 423 K by alternating current (AC) impedance spectroscopy. Full article
(This article belongs to the Special Issue Molecular Conductors)
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556 KiB  
Article
Crystal Structure of the 5-Chloro Salicylamides: Three Different Types of the H-bonding Influenced Linear Chain Formation in the Solid State
by Aleš Imramovský, Karel Pauk, Zdeňka Padělková and Jiří Hanusek
Crystals 2012, 2(2), 349-361; https://doi.org/10.3390/cryst2020349 - 03 May 2012
Cited by 3 | Viewed by 6731
Abstract
Three N-substituted 5-chlorosalicylamides (4-chlorophenyl, 2a; benzyl, 2b; phenethyl 2c) differing in the length of the 'linker' between the benzene ring and the amide moiety were prepared in order to compare their supramolecular architecture. The intramolecular NH···O(H) hydrogen bond and [...] Read more.
Three N-substituted 5-chlorosalicylamides (4-chlorophenyl, 2a; benzyl, 2b; phenethyl 2c) differing in the length of the 'linker' between the benzene ring and the amide moiety were prepared in order to compare their supramolecular architecture. The intramolecular NH···O(H) hydrogen bond and the intermolecular C=O···H–O hydrogen bond were found in the crystal structure of 2a and 2c thus forming an infinite linear chain. Compound 2b had a different arrangement with the intramolecular C=O···H–O hydrogen bond and another intermolecular NH···O(H) hydrogen forming a linear infinite chain. Full article
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639 KiB  
Article
Electroactive Bisiminopyridine Ligands: Synthesis and Complexation Studies
by Gabriela Nita, Diana Branzea, Flavia Pop, Abdelkrim El-Ghayoury and Narcis Avarvari
Crystals 2012, 2(2), 338-348; https://doi.org/10.3390/cryst2020338 - 24 Apr 2012
Cited by 17 | Viewed by 6785
Abstract
The condensation reaction of (4-(6,7-dimethyldithio-tetrathiafulvalene)-aniline) with 2,6-diformylpyridine afforded an electroactive Schiff base (N,N,N) pincer (3). This pincer was reacted with Zn(II) cation to yield the corresponding Zinc chloride complex (4). The crystal structure of the newly prepared electroactive zinc [...] Read more.
The condensation reaction of (4-(6,7-dimethyldithio-tetrathiafulvalene)-aniline) with 2,6-diformylpyridine afforded an electroactive Schiff base (N,N,N) pincer (3). This pincer was reacted with Zn(II) cation to yield the corresponding Zinc chloride complex (4). The crystal structure of the newly prepared electroactive zinc complex reveals that the tetrathiafulvalene (TTF) is neutral and the zinc cation is pentacoordinated. The two chlorines are involved in a set of hydrogen bonds giving rise to a 2D supramolecular grid arrangement. The electronic absorption properties and the electrochemical behavior have been elucidated. These two compounds are promising for the construction of crystalline radical cation salts. Full article
(This article belongs to the Special Issue Molecular Conductors)
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1234 KiB  
Article
Halogen Bonding Interactions in DDQ Charge Transfer Salts with Iodinated TTFs
by Julien Lieffrig, Olivier Jeannin, Kyoung-Soon Shin, Pascale Auban-Senzier and Marc Fourmigué
Crystals 2012, 2(2), 327-337; https://doi.org/10.3390/cryst2020327 - 24 Apr 2012
Cited by 14 | Viewed by 6933
Abstract
Oxidation of 3,4-ethylenedithio-3'-iodo-tetrathiafulvalene (EDT-TTF-I) and 3,4-ethylenedithio-3',4'-diiodo-tetrathiafulvalene (EDT-TTF-I2) with DDQ afforded two different salts formulated as (EDT-TTF-I)(DDQ) and (EDT-TTF-I2)2(DDQ)·(CH3CN), both characterized with a full charge transfer to the DDQ acceptor moiety and by short and linear [...] Read more.
Oxidation of 3,4-ethylenedithio-3'-iodo-tetrathiafulvalene (EDT-TTF-I) and 3,4-ethylenedithio-3',4'-diiodo-tetrathiafulvalene (EDT-TTF-I2) with DDQ afforded two different salts formulated as (EDT-TTF-I)(DDQ) and (EDT-TTF-I2)2(DDQ)·(CH3CN), both characterized with a full charge transfer to the DDQ acceptor moiety and by short and linear halogen bonding interactions between the iodine atom as halogen bond donor, and the carbonyl oxygen or the nitrile nitrogen atoms of reduced DDQ. Full article
(This article belongs to the Special Issue Molecular Conductors)
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1788 KiB  
Article
Polymorphism and Metallic Behavior in BEDT-TTF Radical Salts with Polycyano Anions
by Samia Benmansour, Mathieu Marchivie, Smail Triki and Carlos J. Gómez-García
Crystals 2012, 2(2), 306-326; https://doi.org/10.3390/cryst2020306 - 23 Apr 2012
Cited by 10 | Viewed by 7239
Abstract
Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN)2]32−), two closely related radical salts: α'-(ET)4tcpd·THF (1) [...] Read more.
Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN)2]32−), two closely related radical salts: α'-(ET)4tcpd·THF (1) (THF = tetrahydrofurane) and α'-(ET)4tcpd·H2O (2) have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH (=[(NC)2CC(OCH2CH2OH)C(CN)2]) two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET)2(tcnoetOH) (3) and β''-(ET)2(tcnoetOH) (4). Finally, with the mono-anion tcnoprOH (=[(NC)2CC(OCH2CH2CH2OH)C(CN)2]) we have prepared a metallic radical salt: β''-(ET)2(tcnoprOH)(CH2Cl2CH3Cl)0.5 (5). Salts 14 are semiconductors with high room temperature conductivities and activation energies in the range 0.1–0.5 eV, whereas salt 5 is metallic down to 0.4 K although it does not show any superconducting transition above this temperature. Full article
(This article belongs to the Special Issue Molecular Conductors)
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2052 KiB  
Article
Preparation and Crystal Structure of 5-Azido-3-nitro-1H-1,2,4-triazole, Its Methyl Derivative and Potassium Salt
by Dániel Izsák and Thomas M. Klapötke
Crystals 2012, 2(2), 294-305; https://doi.org/10.3390/cryst2020294 - 23 Apr 2012
Cited by 18 | Viewed by 6570
Abstract
5-Azido-3-nitro-1H-1,2,4-triazole, its methyl derivative and potassium salt were synthesized and characterized by various spectroscopic methods. The crystal structures were determined by low temperature single crystal X-ray diffraction. The interactions between the molecules or ions were analyzed and discussed. Furthermore, all compounds [...] Read more.
5-Azido-3-nitro-1H-1,2,4-triazole, its methyl derivative and potassium salt were synthesized and characterized by various spectroscopic methods. The crystal structures were determined by low temperature single crystal X-ray diffraction. The interactions between the molecules or ions were analyzed and discussed. Furthermore, all compounds were tested according to BAM (Bundesanstalt für Materialforschung und -prüfung) methods. Full article
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1098 KiB  
Article
New BEDT-TTF Radical Cation Salt with Mixed Anions: α'-[BEDT-TTF]2[CuBr2]0.4[CuCl2]0.6
by Kazuya Kubo and Masahiro Yamashita
Crystals 2012, 2(2), 284-293; https://doi.org/10.3390/cryst2020284 - 23 Apr 2012
Cited by 4 | Viewed by 6865
Abstract
A new mixed-anion crystal composed of BEDT-TTF radical cation salt [BEDT-TTF]2(CuBr2)0.4(CuCl2)0.6 with an α'-type donor arrangement with a formal charge of +0.5 per BEDT-TTF was prepared by using a chemical oxidation method and [...] Read more.
A new mixed-anion crystal composed of BEDT-TTF radical cation salt [BEDT-TTF]2(CuBr2)0.4(CuCl2)0.6 with an α'-type donor arrangement with a formal charge of +0.5 per BEDT-TTF was prepared by using a chemical oxidation method and characterized by using X-ray diffraction, four-probe electrical resistivity measurements (semiconductor: ρrt = 2 × 102 Ω cm, Ea = 0.2 eV), and energy band calculations. The results showed that this system had a quasi-one dimensional Fermi surface. Full article
(This article belongs to the Special Issue Molecular Conductors)
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705 KiB  
Review
Theory of Dirac Electrons in Organic Conductors
by Yoshikazu Suzumura and Akito Kobayashi
Crystals 2012, 2(2), 266-283; https://doi.org/10.3390/cryst2020266 - 20 Apr 2012
Cited by 10 | Viewed by 6852
Abstract
The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon [...] Read more.
The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon for the intermediate magnitude of momentum owing to the combined effects of two tilted cones. Dirac electrons with the zero-gap state (ZGS) in organic conductor α-(BEDT-TTF)2I3 are examined by calculating the Berry curvature, which displays the peak structure for a pair of Dirac particles between the conduction band and the valence band. The ZGS is theoretically predicted for α-(BEDT-TTF)2NH4Hg(SCN)4 under uniaxial pressure. Examining the band structure of the stripe charge ordered state of α-(BEDT-TTF)2I3 under pressure, we have found a topological transition from a conventional insulator to a new phase of a pair of Dirac electrons with a finite mass. Further, investigating the zero-energy (N = 0) Landau level under a strong magnetic field, we propose ferromagnetism breaking the SU(2) valley-pseudo-spin symmetry, and the phase fluctuations of the order parameters leading to Kosterlitz-Thouless transition at lower temperatures. Full article
(This article belongs to the Special Issue Molecular Conductors)
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949 KiB  
Review
Superconductivity in Layered Organic Metals
by Jochen Wosnitza
Crystals 2012, 2(2), 248-265; https://doi.org/10.3390/cryst2020248 - 19 Apr 2012
Cited by 31 | Viewed by 7101
Abstract
In this short review, I will give an overview on the current understanding of the superconductivity in quasi-two-dimensional organic metals. Thereby, I will focus on charge-transfer salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET for short). In these materials, strong electronic correlations are clearly [...] Read more.
In this short review, I will give an overview on the current understanding of the superconductivity in quasi-two-dimensional organic metals. Thereby, I will focus on charge-transfer salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET for short). In these materials, strong electronic correlations are clearly evident, resulting in unique phase diagrams. The layered crystallographic structure leads to highly anisotropic electronic as well as superconducting properties. The corresponding very high orbital critical field for in-plane magnetic-field alignment allows for the occurrence of the Fulde–Ferrell– Larkin–Ovchinnikov state as evidenced by thermodynamic measurements. The experimental picture on the nature of the superconducting state is still controversial with evidence both for unconventional as well as for BCS-like superconductivity. Full article
(This article belongs to the Special Issue Molecular Conductors)
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111 KiB  
Article
Equivalence of Electron-Vibration Interaction and Charge-Induced Force Variations: A New O(1) Approach to an Old Problem
by Benjamin J. Powell, Tunna Baruah and Mark R. Pederson
Crystals 2012, 2(2), 236-247; https://doi.org/10.3390/cryst2020236 - 18 Apr 2012
Viewed by 5701
Abstract
Calculating electron-vibration (vibronic) interaction constants is computationally expensive. For molecules containing N nuclei it involves solving the Schrödinger equation for Ο(3N) nuclear configurations in addition to the cost of determining the vibrational modes. We show that quantum vibronic interactions are proportional to [...] Read more.
Calculating electron-vibration (vibronic) interaction constants is computationally expensive. For molecules containing N nuclei it involves solving the Schrödinger equation for Ο(3N) nuclear configurations in addition to the cost of determining the vibrational modes. We show that quantum vibronic interactions are proportional to the classical atomic forces induced when the total charge of the system is varied. This enables the calculation of vibronic interaction constants from O(1) solutions of the Schrödinger equation. We demonstrate that the O(1) approach produces numerically accurate results by calculating the vibronic interaction constants for several molecules. We investigate the role of molecular vibrations in the Mott transition in κ-(BEDT-TTF)2Cu[N(CN)2]Br. Full article
(This article belongs to the Special Issue Molecular Conductors)
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942 KiB  
Article
Properties of Mn2+ and Π-Electron Spin Systems Probed by 1H and 13C NMR in the Organic Conductor κ-(BETS)2Mn[N(CN)2]3
by Oleg M. Vyaselev, Reizo Kato, Hiroshi M. Yamamoto, Megumi Kobayashi, Leokadiya V. Zorina, Sergey V. Simonov, Nataliya D. Kushch and Eduard B. Yagubskii
Crystals 2012, 2(2), 224-235; https://doi.org/10.3390/cryst2020224 - 12 Apr 2012
Cited by 11 | Viewed by 5723
Abstract
Properties of the spin systems of the localized 3d Mn2+ ions and the conduction π electrons in quasi-two-dimensional organic conductor κ-(BETS)2Mn[N(CN)2]3 were accessed using 1H and 13C NMR in order to find their [...] Read more.
Properties of the spin systems of the localized 3d Mn2+ ions and the conduction π electrons in quasi-two-dimensional organic conductor κ-(BETS)2Mn[N(CN)2]3 were accessed using 1H and 13C NMR in order to find their relation to the metal-insulator transition which occurs at ∼23 K. The transition of the system into the insulating state is shown to be followed by localization of the π spins into a long-range ordered staggered structure of AF type. In contrast, the 3d Mn2+ electron spin moments form a disordered tilted structure, which may signify their trend to AF order, frustrated geometrically by the triangular arrangement of Mn in the anion layer. This result suggests that the MI transition in κ-(BETS)2Mn[N(CN)2]3 is not the consequence of the interactions within the Mn2+ spins but due to the interactions within the π-electron system itself. Vice versa, it is more likelythat the disordered tilted structure of the Mn2+ spins is induced by the ordered π-spins via the π-d interaction. Full article
(This article belongs to the Special Issue Molecular Conductors)
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621 KiB  
Article
Synthesis and Crystal Structures of the Quaternary Zintl Phases RbNa8Ga3Pn6 (Pn = P, As) and Na10NbGaAs6
by Hua He, Chauntae Tyson and Svilen Bobev
Crystals 2012, 2(2), 213-223; https://doi.org/10.3390/cryst2020213 - 11 Apr 2012
Cited by 8 | Viewed by 5480
Abstract
The new Zintl compounds RbNa8Ga3Pn6 (Pn = P, As) and Na10NbGaAs6 have been synthesized from the corresponding elements at high temperatures. RbNa8Ga3P6 and RbNa8Ga3As6 [...] Read more.
The new Zintl compounds RbNa8Ga3Pn6 (Pn = P, As) and Na10NbGaAs6 have been synthesized from the corresponding elements at high temperatures. RbNa8Ga3P6 and RbNa8Ga3As6 crystallize with a novel structure type that features trigonal planar [Ga3P6]9 and [Ga3As6]9 motifs, which are isosteric with the 1,3,5-trioxanetrione (a cyclic trimer of carbon dioxide). Na10NbGaAs6, an unforeseen side product of the same reactions boasts a structure, which is based on NbAs4 and GaAs4 tetrahedra, condensed by sharing common edges into [NbGaAs6]10– dimers. The bonding characteristics of both structures are discussed. All three compounds reported herein represent the first compounds found in the respective quaternary systems. Full article
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