Molecular conductors based on selenium isologs of DMIT

Abstract

The study of [(CH3)4N]x[ML2]-chelates (x = 0.5 − 2) with M = Ni, Pd, Pt and L = dmit (1,3-dithiole-2-thione-4,5-dithiolate), dmise (1,3-dithiole-2-selone-4,5-dithiolate), dsit (1,3-dithiole-2-thione-4,5-diselenolate), dsise (1,3-dithiole-2-selone-4,5-diselenolate) and dsis (1,3-diselenole-2-selone-4,5-diselenolate) shows distinct effects of the variation of the number of selenium and sulfur atoms on the redox and conducting properties.With increasing number of selenium atoms in the investigated compounds and subsequent decreasing number of sulfur atoms the oxidation potentials for the preparation of higher oxidized compounds (x < 1) decrease. The conductivity of these partially oxidized chelates decreases in the same order.In the crystal structure of [(CH3)4N]0.5[Ni(dsise)2] (space group Pccn, a = 7.423(3), b = 39.134(7), c = 11.829(4) Å) the formation of [Ni((dsise)2] dimeric units is detectable, in which the nickel atom is square pyramidal coordinated by five selenium atoms. The room temperature conductivity of this chelate is high (12 S cm−1), but the temperature dependance of the conductivity is characteristic for semiconductors (0.06 eV). Therefore the difference when compared to the corresponding superconducting “all sulfur-compound” [(CH3)4N]0.5[Ni(dmit)2] is significant.