Synthesis of the new organic metal bis[bis(ethylenedithio)tetrathiafulvalene] tricyanomethanide and characterization of its metal-insulator phase transition at .apprx.180 K

A new conducting salt (ET)/sub 2/C(CN)/sub 3/, the first 2:1 salt of ET (i.e., bis(ethylenedithio)tetrathiafulvalene) with a planar-triangular anion, was synthesized, and its structure was determined by single-crystal x-ray diffraction. Crystals data for (ET)/sub 2/C(CN)/sub 3/ are as follows: monoclinic, P2/a, Z = 2; at 125 K/298 K, a = 14.684 (8)/14.979 (7) /angstrom/, b = 6.667 (3)/6.700 (2) /angstrom/, c = 16.400 (6)/ 16.395 (4) /angstrom/, /beta/ = 95.13 (3)/94.80 (3)/degree/, and V/sub c/ = 1599 (1)/1639.7 (9) /angstrom//sup 3/. The electrical conductivity of this salt as a function of temperature shows that it undergoes a metal-insulator phase transition at /approx/ 180 K. The magnetic susceptibility measured as a function of temperature and the tight-binding band electronic structure for (ET)/sub 2/C(CN)/sub 3/ show that the phase transition at /approx/ 180 K is a Peierls type metal-insulator transition. The band electronic structure of (ET)/sub 2/C(CN)/sub 3/ predicts a doubling of the b axis as a consequence of the Peierls distortion, which had been confirmed by the use of x-ray photographs of (ET)/sub 2/C(CN)/sub 3/ taken as a function of temperature. 26 refs., 8 figs., 1 tab..