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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.