CRYSTAL-STRUCTURES OF THE ORGANIC METALS (ET)2[HG-(SCN)CL2] AND (ET)2[HG(SCN)2BR]

The compositions and structures of two new organic metals based on ET [where ET = bis(ethylenedithio)tetrathiafulvalene], viz., (ET)2[Hg)SCN )Cl2], with a metal-dielectric transition temperature (T(m-d)) of 35-d egrees-K, and (ET)2[Hg(SCN)2Br], with T(m-d) = 140-degrees-K, were est ablished by x-ray diffraction analysis. The crystal structures of the investigated compounds are similar to the structure of the previously studied organic metal (ET)2[Hg(SCN)2Cl] with T(m-d) = 50-degrees-K. Th e principal crystallographic data for (ET)2[Hg(SCN)Cl2] are as follows : a = 36.64(1), b = 8.300(4), c = 11.798(1) angstrom, beta = 89.91(3)- degrees, V = 3588.1(9) angstrom3, space group Cc, Z = 4, d(calc) = 2.0 5 g/cm3. The principal crystallographic data for (ET)2[Hg(SCN)2Br] are as follows: a = 37 088(14), b = 8.338(3), c = 11.738(5) angstrom, bet a = 89.71(3)-degrees, V = 3629.6(8) angstrom3, space group C2/c, Z = 8 , d(calc) = 2.15 g/cm3. A characteristic feature of the crystal struct ure of the investigated compounds is alternation of the anion and cati on layers along the a axis of the crystal in the cation layer of the k type the ET are interconnected by shortened S...S intermolecular cont acts (3.39-3.58 angstrom). The [Hg(SCN)3-nXn]- anions (X = Cl, Br; n = 1, 2) form polymeric chains with one or two bridged SCN groups. A ten dency for a decrease in the metal-dielectric transition temperature wi th a decrease in the volume of the anion is detected in the (ET)2[Hg(S CN)3-nXn] salts, where X = Cl and Br, and n = 1 and 2.