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

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Open AccessArticle Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range
Crystals 2012, 2(2), 710-729; https://doi.org/10.3390/cryst2020710
Received: 7 February 2012 / Revised: 14 June 2012 / Accepted: 14 June 2012 / Published: 20 June 2012
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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,
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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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Open AccessArticle Ru11Lu20, a New Intermetallic Compound with Eight- to Ten-Coordinate Ruthenium Atoms
Crystals 2012, 2(2), 704-709; https://doi.org/10.3390/cryst2020704
Received: 14 May 2012 / Revised: 11 June 2012 / Accepted: 12 June 2012 / Published: 20 June 2012
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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
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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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Open AccessArticle Silica-Metal Composite for Hydrogen Storage Applications
Crystals 2012, 2(2), 690-703; https://doi.org/10.3390/cryst2020690
Received: 2 February 2012 / Revised: 23 May 2012 / Accepted: 6 June 2012 / Published: 18 June 2012
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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
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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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Open AccessArticle Inorganic Amino-Nitro-Guanidinium Derivatives
Crystals 2012, 2(2), 675-689; https://doi.org/10.3390/cryst2020675
Received: 2 May 2012 / Revised: 6 June 2012 / Accepted: 7 June 2012 / Published: 18 June 2012
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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
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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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Open AccessCommunication Non-Covalent Interactions in the Crystal Structure of Methyl 4-Hydroxy-3-Nitrobenzoate
Crystals 2012, 2(2), 669-674; https://doi.org/10.3390/cryst2020669
Received: 18 April 2012 / Revised: 22 May 2012 / Accepted: 1 June 2012 / Published: 12 June 2012
Cited by 1 | PDF Full-text (338 KB) | HTML Full-text | XML Full-text | Supplementary Files
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),
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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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Open AccessArticle Single-Component Charge-Transfer Crystals Based on Spin-Carrying TCNQ (7,7,8,8-Tetracyanoquinodimethane) Derivatives
Crystals 2012, 2(2), 662-668; https://doi.org/10.3390/cryst2020662
Received: 16 March 2012 / Revised: 1 June 2012 / Accepted: 5 June 2012 / Published: 12 June 2012
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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
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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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Open AccessReview Transport Phenomena in Multilayered Massless Dirac Fermion System α-(BEDT-TTF)2I3
Crystals 2012, 2(2), 643-661; https://doi.org/10.3390/cryst2020643
Received: 14 March 2012 / Revised: 28 May 2012 / Accepted: 29 May 2012 / Published: 11 June 2012
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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
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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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Open AccessArticle Single-Crystal-to-Single-Crystal Transformation from δ-(BEDT-TTF)4[OsNOCl5]1.33(C6H5NO2)0.67 to β"-(BEDT-TTF)3[OsNOCl5]
Crystals 2012, 2(2), 627-642; https://doi.org/10.3390/cryst2020627
Received: 16 March 2012 / Revised: 15 May 2012 / Accepted: 15 May 2012 / Published: 7 June 2012
Cited by 1 | PDF Full-text (1345 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
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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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Open AccessArticle Growth Mechanisms of CdS Nanocrystals in Aqueous Media
Crystals 2012, 2(2), 618-626; https://doi.org/10.3390/cryst2020618
Received: 7 December 2011 / Revised: 16 May 2012 / Accepted: 23 May 2012 / Published: 6 June 2012
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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
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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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Open AccessReview Photoinduced Phase Transitions in α-, θ-, and κ-type ET Salts: Ultrafast Melting of the Electronic Ordering
Crystals 2012, 2(2), 590-617; https://doi.org/10.3390/cryst2020590
Received: 14 March 2012 / Revised: 23 April 2012 / Accepted: 24 April 2012 / Published: 30 May 2012
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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
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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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Open AccessArticle Spin and Charge Transport in the X-ray Irradiated Quasi-2D Layered Compound: κ-(BEDT-TTF)2Cu[N(CN)2]Cl
Crystals 2012, 2(2), 579-589; https://doi.org/10.3390/cryst2020579
Received: 23 March 2012 / Revised: 25 April 2012 / Accepted: 11 May 2012 / Published: 24 May 2012
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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
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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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Open AccessArticle Comprehensive Optical Investigations of Charge Order in Organic Chain Compounds (TMTTF)2X
Crystals 2012, 2(2), 528-578; https://doi.org/10.3390/cryst2020528
Received: 2 March 2012 / Revised: 30 April 2012 / Accepted: 1 May 2012 / Published: 23 May 2012
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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
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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)
Open AccessCommunication Ethyl 2,6-Dimethoxybenzoate: Synthesis, Spectroscopic and X-ray Crystallographic Analysis
Crystals 2012, 2(2), 521-527; https://doi.org/10.3390/cryst2020521
Received: 19 March 2012 / Revised: 4 May 2012 / Accepted: 9 May 2012 / Published: 22 May 2012
Cited by 3 | PDF Full-text (230 KB) | HTML Full-text | XML Full-text | Supplementary Files
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.
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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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Open AccessReview Structural Aspects of the Bechgaard and Fabre Salts: An Update
Crystals 2012, 2(2), 466-520; https://doi.org/10.3390/cryst2020466
Received: 20 March 2012 / Revised: 19 April 2012 / Accepted: 20 April 2012 / Published: 21 May 2012
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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
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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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Open AccessArticle Synthesis, Structure and Solid State Properties of Cyclohexanemethylamine Substituted Phenalenyl Based Molecular Conductor
Crystals 2012, 2(2), 446-465; https://doi.org/10.3390/cryst2020446
Received: 30 March 2012 / Revised: 20 April 2012 / Accepted: 2 May 2012 / Published: 14 May 2012
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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
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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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