X-RAY STRUCTURE OF THE ORGANIC CONDUCTOR (ET)8[HG2BR6.PHBR]2

The electrochemical oxidation of ET [bis(ethylenedithio)tetrathiafulvalene] in bromobenzene (electrolyte Bu4N[HgBr3]) gave the radical-cation salt (ET)8[Hg2Br6.PhBr]2 (1), a new organic metal with a temperature range of 300-125 K. At 125 K a metal-dielectric transition is observed. Crystallographic data for (1): a = 19.171(6), b = 12.668(4), c = 17.777(6) angstrom, alpha = 118.03(3), beta = 89.45(2), gamma = 101.21(3)-degrees, P1BAR, Z = 1 d(calc) = 2.30 g/cm3. The crystal structure of (1) is laminar. In the conducting organic layer the ET radical cations are linked into bands by shortened intermolecular S...S contacts of the "side-to-side " type. The anionic layer consists of centrosymmetric complexes [Hg2Br6.C6H5Br]24-. The Hg1 and Hg2 atoms are characterized by a trigonal configuration of the Hg-Br bond which is built up, on account of secondary Hg...Br interactions, into trigonal-bipyramidal for Hg1 and trigonal-pyramidal (tetrahedral)for Hg2. Interaction between the anionic and cationic layers is effected through Br6...S8 contacts [3.491(7) angstrom)].