MOLECULAR CONDUCTORS BASED ON SELENIUM ISOLOGS OF DMIT

The study of [(CH3)4N]X[ML2]-chelates (x = 0.5 - 2) with M = Ni, Pd, P t and L = dmit (1,3-dithiole-2-thione-4,5-dithiolate), dmise (1,3-dith iole-2-selone-4,5-dithiolate), dsit (1,3-dithiole-2-thione-4,5-diselen olate), dsise (1,3-dithiole-2-selone-4,5-diselenolate) and dsis (1,3-d iselenole-2-selone-4,5,diselenolate) shows distinct effects of the var iation of the number of selenium and sulfur atoms on the redox and con ducting properties. With increasing number of selenium atoms in the in vestigated compounds and subsequent decreasing number of sulfur atoms the oxidation potentials for the preparation of higher oxidized compou nds (x < 1) decrease. The conductivity of these partially oxidized che lates decreases in the same order. In the crystal structure of [(CH3)4 N]0.5[Ni(dsise)2] (space group Pccn, a - 7.423(3), b = 39.134(7), c = 11.829(4) angstrom) the formation of [Ni(dsise)2] dimeric units is det ectable, in which the nickel atom is square pyramidal coordinated by f ive selenium atoms. The room temperature conductivity of this chelate is high (12 S cm-1), but the temperature dependance of the conductivit y is characteristic for semiconductors (0.06 eV). Therefore the differ ence when compared to the corresponding superconducting ''all sulfur-c ompound'' [(CH3)4N]0.5[Ni(dmit)2] is significant.