G. Bravic

Determining the charge distribution in BEDT-TTF salts

The intramolecular bond lengths of the donor BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene, also ET) are sensitive to the charge carried by the molecule. By considering a large number of ET salts, we have developed a method for determining experimentally the charges of the ET molecules. The standard deviation in charge is only 0.1 for high quality structures.

(BEDT-TTF)2GaCl4 : structure, electrical and magnetic properties

Abstract We report the synthesis, crystal structure, electrical transport and magnetic properties of (BEDT-TTF) 2 GaCl 4 . It crystallises in a triclinic system, P 1 , a =31.911, b =16.580, c =6.645 A , α=98.15, s=85.60, γ=90.55°, Z =4 and V =3470 A 3 with stacks of twisted dimers. σ RT (to c) = 0.1 Scm −1 and E A = 0.21 eV. The susceptibility is anisotropic; χ(to c) behaves as a 1D antiferromagnetic chain and χ( 1 to c) is activated with E A ∼ 9meV.

Structural properties of two modifications of hydrated BEDT-TTF chloride salts

Abstract 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). The room temperature crystal structure of (I) the 3/2 stoichiometry and (II) the 4/4 stoichiometry compounds were already known. (I) has been measured at low temperature (50K) to look for the structural changes associated with the variations of the physical properties near 110K. The latter has been correlated with the modification of the thermal expansion anisotropy in the stacking direction of BEDT-TTF cations, the [010] crystallographic direction. The new 4/6 salt (III) is the third hydrated BEDT-TTF chloride known up to date. It differs from the others by the space group. As for the precedent forms one can see a 2D arrangement of anionic and cationic sheets alternating along the [100] crystallographic direction, but there are two orientations for the BEDT-TTF planes and two kinds of overlapping modes of these molecules.

(BEDT-TTF)3[CuBr4]

The crystal structure of the title compound, tris[3,4,3,4-bis(ethylenedithio)-2,2,5,5-tetrathiafulvalene] tetrabromocuprate(2−), (C 10 H 8 S 8 ) 3 [CuBr 4 ], is classified as the α phase and contains two independent BEDT-TTF [BEDT-TTF = 3,4,3,4-bis(ethylenedithio)-2,2,5,5-tetrathiafulvalene] molecules (A and B) stacked as ABBABB along the c axis. The dihedral angle between the A and B molecules is 5.3 (1)° and between the stacks is 67.1 (2)°. The shortest intermolecular distances observed between molecules in adjacent columns are S...S 3.485 (2) and S...C 3.428 (4) A, and between anions and cations Br...S 3.777 (1) A

Structural and zeolitic features of a series of heterometallic supramolecular porous architectures based on tetrahedral {M(C2O4)4}4− primary building units

The utilization of tetrahedral pre-formed coordination compounds {M(C2O4)4}4- (M = Zr(IV), U(IV); C2O4(2-) = oxalate) permitted the efficient construction of rare examples of heteronuclear supramolecular nano-porous architectures. A series of metal-organic coordination frameworks prepared by association of these building units with either Mn2+, Cd2+, or Mg2+ have been structurally characterized and are described. Their 3-D chemical scaffold is based on the primary tetrahedral building unit but their pore sizes and topologies could be varied through the M2+ metal ion involved in the assembling process, and the anionic tetrahedral moiety. These structures display channels with apertures up to 12 Angstrom x 8 Angstrom which are emptied of solvates at mild temperatures without affecting the chemical scaffold, the integrity of which is maintained up to 250-300 degrees C. A certain degree of flexibility of the coordination polymers upon guest release is suggested by the temperature dependence of the powder X-ray patterns and N2 sorption experiments, but reversible and selective sorption of small molecules has been observed substantiating that these open-frameworks behave like sponges.

Pressure and temperature dependence of the structural properties of the molecular semiconducting salt: α'-(BEDT-TTF)2Ag(CN)2

Abstract The temperature and pressure dependence of the electrical conductivity of the α-(BEDT-TTF) 2 Ag(CN) 2 salt shows a transition between two semiconducting phases at a critical temperature depending on pressure. This transition is crystallographically characterized by the appearance of a superstructure corresponding to the doubling of the b parameter. We present and discuss here the parameters evolution at decreasing temperature and increasing pressure and the structural evolution under constraints.

Temperature dependence (300 to 10K) of the structural and electronic properties of the molecular charge-transfer salt (BEDT-TTF)3 Cl2,2H2O

Abstract The crystal and electronic structure of the molecular charge-transfer salt (BEDT-TTF) 3 Cl 2 2H 2 O was determined at 10, 130, 190 and 295K. The thermal expansion has been evaluated from measurements of cell parameters between 10 and 295K.

Structure of (η5-cyclopentadienyl)(η6-1,3,5-trimethylbenzene)iron-7,7,8,8-tetracyano-p-quinodimethane (1/2)

[Fe(C 9 H 19 )(C 5 H 5 )](C 12 H 4 N 4 ) 2 cristallise dans P2 1 /m avec a = 7,914, b = 30,983 et c = 6,629 A, β = 102,38 °, Z = 2; affinement jusqua R = 0,042. La structure consiste en couches de TCNQ separees par le ferrocene. Les effets steriques des groupes methyl ne se manifestent pas seulement sur le metallocene, mais egalement sur lempilement du TCNQ.

High pressure and low temperature X-ray crystallography: the crystal structure of the molecular charge transfer salt α'- (bis(ethylenedithio)-tetrathiafulvalene)2AuBr2

An X-ray diffraction technique is described that allows determination of crystal structure and the variation of lattice parameters of single crystals as a function of hydrostatic pressure up to 14 kbar and of temperature from 300 K to 12 K. As an example of the technique results are presented on the molecular charge transfer salt α-(BEDT TTF)2AuBr2 (BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalene) to elucidate the nature of a structural phase transition which occurs at 250 K at ambient pressure and 7 kbar at 300 K. The transition, of second order, is characterized by the appearance of ½b* superlattice reflections at high pressure or low temperature but without any drastic change in the basic crystal structure. The isobaric thermal expansions and the isothermal compressibilities are anisotropic, being larger along a than along b and c, though of different magnitudes and directional properties, i. e. the effect of applying pressure at ambient temperature is not equivalent to lowering the temperature at ambient pressure. Transfer integral calculations show that marked dimerization along the stacking axis, already present at 300 K, is related to electronic localization.

Interaction Between Furocoumarins and Pyrimidine Bases in a Linked System. The Crucial Choice of the Link

Abstract A specific interaction between psoralen and pyrimidine bases (thymine), revealed in crystals of compound III, induced under UV light a topochemical photocycloaddition between the double bonds of thymine and pyrone ring of psoralen. The crystallographic analysis of compound I, II and III demonstrated the minor perturbation displayed by the trioxyethylene chain on the chromophore packing modes.