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Abstract:: The crystal structure of (TMTSF)2ClO4 has been determined at (7 K, 1 bar) and at (7 K, 5 kbar) with a high accuracy. For the latter, low temperature and pressure were applied simultaneously using a X-ray diffraction instrumentation designed in our laboratory, these results are the first for molecular compounds. The effects of lowering the temperature are not the same as those produced by increasing the pressure. At (7 K, 1 bar) the anion ordering which occurs in this compound, and which is characterised by the appearance of b * /2 superlattice reflections, is well observed. This anion ordering leads to the presence of two independent stacks of TMTSF cations which is the only case found in the Bechgaard salts family. The comparison of the low temperature crystal structures under atmospheric pressure and at 5 kbar shows that the centres of mass are nearly the same, independent of the pressure: the interchain interactions do not depend on the doubling of the unit cell. Under pressure, the ordering (0, 1/2, 0) does not occur at any temperature. These structural data are confirmed by the quantum chemical calculations which show that the difference in the site energy of the two independent cations is 100 meV.

The effect of the first-order phase transition occurring around 220K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)"2ReO"4.H"2O has been studied. The crystal structure at 170K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO"4^- anions. This rotation leads to changes in the S...S and S...O intermolecular contacts within the BEDO-TTF donor layers, nevertheless the band structure is remained practically unchanged. Possible changes in the crystal structure which can occur at room temperature depending on the experimental conditions are considered. It seems very likely that the (BEDO-TTF)"2ReO"4.H"2O crystal loses its water molecules in the vacuum and hence changes its crystal structure.

The physical properties of the charge-transfer salt DEDMTSF-TCNQ are reviewed in the light of the hitherto unknown room temperature X-ray crystal structure and some new magnetic measurements. DEDMTSF-TCNQ crystallizes in the triclinic lattice P1 with the unit cell parameters: a = 7.598(5)Å, b = 19.755(8)Å, c = 3.931(4)Å, α = 88.22(7)O, β = 94.45(7)O and γ = 9.57(7)O. No disorder between ethyl and methyl groups in the donor stacks is seen in the structure determination. Apparently only the trans-configuration is present. Nevertheless, the very broad phase transition is attributed to disorder caused by either small domains of the insulating crystal habit in the material or to the presence of small amounts of cis-DEDMTSF not detected by the X-rays.

Un certain nombre de corrélations entre propriétés électriques et propriétés structurales des sels semi-conducteurs du tétracyanoquinodiméthane (TCNQ) ont déjagrave; été établies.1 L'examen comparé de nouveaux complexes ainsi qu'une étude en variation de température permettent de préciser ces corrélations.

La synthèse d'un complexe de transfert de charge du tétracyanoquinodiméthane (TCNQ) dopé avec de l'iode a été le point de départ de cette étude. En effet, l'iode peut, soit se mettre sous la forme d'une chaine atomique donc étre un exemple de système unidimensionnel, soit former des complexes de transfert de charge avec anion diamagnétique et cependant bons semiconducteurs.

We have synthetized and purified the dimethyltrime-thylene tetraselenafulvalene (DMtTSeF). From this unsymmetrical molecule a series of radical cation salts has been prepared by electro-oxidation. This new series, isostoicheiometric and isomorphous with the TMTSeF salts, exhibits a metallic behavior down to 0,1 K without any sign of either a metal-insulator or a superconducting phase transition.

(BEDTTTF)2SbF6 and (BEDTTTF)2AsF6 Show a metal-insulator transition close to room temperature. We present the D.C. electrical and E.P.R. measurements together with the structural investigations.

The structure and physical properties of tetramethyl-tetrathiofulvalène (TMTTF) salts are reviewed. New results are given about (TMTTF)2 PF6, (TMTTF)2 ClO4 and the selenium analog (TMTSF)2 ClO4. An experimental relationship is shown between the electrical and magnetic properties and the closest contacts S-S or Se-Se of neighbouring stacks.

We report the synthesis, crystal structure, electrical transport and magnetic properties of (BEDT-TTF)2GaCl4. It crystallises in a triclinic system, P1, a=31.911, b=16.580, c=6.645Å, α=98.15, ß=85.60, γ=90.55°, Z=4 and V=3470Å3with stacks of twisted dimers. σRT(to c) = 0.1 Scm−1and EA= 0.21 eV. The susceptibility is anisotropic; χ(to c) behaves as a 1D antiferromagnetic chain and χ(1to c) is activated with EA∼ 9meV.

We report the compressibility tensor calculated from the pressure dependence (< 13kbar) of the cell parameters and the structural and electronic properties derived from the high pressure (7.5kbar) crystal structure of the title compound.

In this paper are presented two modifications of hydrated chlorides of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF)xCl2, yH2O with stoichiometries x=3, y=2(I) and x=4, y=6 (III).

A new homologous series of 4-(4'-ethoxybenzoyloxy)-2-alkoxy-4'-(4-butoxysalicylaldimine)-azobenzenes has been synthesized. These compounds contain four rings in the main core and a lateral alkoxy branch on one of the inner rings and present enantiotropic nematic properties. The X-ray crystal structure (MoKα radiation, λ = 0.7071 Å, graphite monochromator) of 4-(4'-ethoxybenzoyloxy)-2-butoxy-4'-(4-butoxysalicylaldimine)azobenzene was investigated (T = 293K, R = 0.059 for the 2855 observed reflections). This compound (C36H39N3O6) crystallizes in the monoclinic system with C2/c space group; (Z = 8); a = 28.052(7) A, b = 7.545(4) Å, c = 33.823(7) Å and β = 112.70(1)°. There is a strong chelated hydrogen bond between the OH group and the neighbouring nitrogen atom engaged in the imine bridge. In the solid state, the molecule is roughly linear with a 31 Å length. The lateral butoxy chain is quasi-perpendicular to the long axis of the main core. The crystal cohesion is due to numerous Van der Waals interactions. At the solid to nematic transition, a change in the conformation of the lateral chain occurs from an all trans-conformation to one involving a cis-conformation in the first part of the lateral chain. This change can be monitored by the evolution of the 13C chemical shift of the OCH2 belonging to the lateral alkoxy chain.

AbstractUp to now, very few results concerning the crystal structure of molecular compounds have been obtained by X-ray diffraction under pressure; such an experiment has been set up in our laboratory and several molecular superconductors have been studied for the last five years. We report, besides some technical information about the method, the compressibility tensor calculated from the pressure dependence(<12kbar) of the cell parameters and the structural and electronic properties of the organic superconductor (TMTSF)2CIO4derived from the complete X-ray crystal structure determination, performed at 4,6 and 9. 5kbar.

The low temperature crystal packing of (TSeT)"2Cl is similar to that obtained at room temperature, no structural transition occuring. Only small changes in the atomic parameters are observed. On the contrary, the high pressure and the high pressure-low temperature crystal structures show a change in the symmetry which leads to a difference in the network of the chloride anions and in their environment.

The ordering of the anion in the molecular conductor salt (TMTSF)"2NO"3 at low temperature depends on the rate of cooling and corresponds to the doubling of the a cell parameter. This order-disorder transition does not affect the crystal packing as the TMTSF chains in the ordered and in the disordered crystal structures at 12K can not be distinguished. This salt is strongly 1D at low temperature.

The anion ordering which occurs in (TMTSF)2ClO4 at 24 K is characterized by the appearance of b*/2 superlattice reflections, without any important change in the basic crystal structure. The intensities of these superlattice reflections have been measured at 7 K (ambient pressure). At the same temperature, these reflections do not appear under pressure (5 kbar). Thus, in the latter case, the anions remain disordered.

The anion ordering which occurs in (TMTSF)2ClO4at 24 K is characterized by the appearance of b*/2 superlattice reflections, without any important change in the basic crystal structure. The intensities of these superlattice reflections have been measured at 7 K (ambient pressure). At the same temperature, these reflections do not appear under pressure (5 kbar). Thus, in the latter case, the anions remain disordered.

Tris(ethylenedithio)benzene (VIII) is prepared from 1,3,5‐trichlorobenzene (I) as shown in the reaction scheme.