Electrocrystallization and characterization of phosphonium-based radical anion salts [MePh3P][Pd(dmit)2]3 and [Ph4P][Pd(dmit)2]3 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate).: Comparison with related Pd and Ni isologues

The two new radical anion salts [MePh3P] [Pd(dmit)(2)](3) (1) (dmit= C3S52- = 1,3-dithiole-2-thione-4,5-dithiolate) and [Ph4P]-[Pd(dmit)(2)](3) (2) have been synthesized and characterized by X-ray diffraction, elemental analysis and temperature-dependent conductivity measurements. Complexes 1 and 2 were prepared via electrooxidation of [Pd( dmit)(2)](2-) in acetonitrile-acetone solvent mixtures at a Pt wire anode in the presence of methyltriphenylphosphonium bromide and tetraphenylphosphonium bromide electrolytes, respectively. For [MePh3P] [Pd(dmit)(2)](3) (1), black shiny needle and platelet crystals suitable for X-ray analysis were obtained. The crystal packing structure consists of layers of Pd(dmit)(2) units separated by layers of MePh3P+ counterions. The Pd(dmit)(2) layers are composed of dimers of Pd(dmit)(2) units as a result of strong Pd ... Pd interactions. Extensive S ... S nonbonding interdimer interactions are observed, with each dimer interacting with six other adjacent dimers. For [Ph4P] [Pd(dmit)(2)](3) (2), black shiny hat needles were harvested and the stoichiometry confirmed by elemental analysis. Single-crystal temperature-dependent conductivity measurements show that 1 behaves as a semiconductor with a room-temperature conductivity of 13 S cm(-1) and a thermal activation energy of 100 meV. Compound 2 also displays semiconducting behavior with a room-temperature conductivity of 0.8-1 S cm(-1) and a thermal activation energy of 55 meV. (C) 1998 Elsevier Science S.A. All rights reserved.