SYNTHESIS, CRYSTAL-STRUCTURE AND ELECTRICAL-PROPERTIES OF 2 NEW PALLADIUM COMPLEXES OF SELENIUM AND SULFUR LIGANDS - [NME(4)][PD(C3S3SE2)(2)](2) AND [PME(4)][PD(C3S5)(2)](2)

The compounds [NMe(4)][Pd(C3S3Se2)(2)](2) and [PMe(4)][Pd(C3S5)(2)](2) [C3S3Se2 = 4,5-bis(hydroseleno)-1,3-dithiole-2-thionate; C3S5 = 4,5-d imercapto-1,3-dithiole-2-thionate] have been prepared by electro-chemi cal oxidation of [NBu(4)](2)[Pd(C3S3Se2)(2)] and [NBu(4)][Pd(C3S5)(2)] in the presence of a large excess of NMe(4)PF(6) and PMe(4)I, respect ively. Their structures have been determined by X-ray crystallographic methods. Both compounds, with space group C2/c, are isostructural to the superconducting phase beta-[NMe(4)][Pd(C3S5)(2)](2). The PdL(2) (L = C3S3Se2 or C3S5) entities are paired, forming [(PdL(2))(2)] dimer l ayers in the (001) plane separated from each other by sheets of cation s. The dimers are stacked along [110] and [$($) over bar$$ 110]. Both compounds show similar electrical properties: the room-temperature con ductivities are approximate to 50 and approximate to 20 S cm(-1), resp ectively; at high temperature the conductivity is weakly temperature d ependent, but abruptly decreases at low temperatures; the conductivity increases when applying pressure. A broad dispersion of optical excit ations was observed in the reflectance spectra of [NMe(4)][Pd(C3S3Se2) (2)](2), indicating an overlap of the highest occupied (HOMO) and lowe st unoccupied molecular orbital (LUMO) bands and a HOMO-type conductio n band.