SEMICONDUCTOR PROPERTIES OF TRANSITION METAL CHELATES OF LIGANDS DERIVED FROM ALPHA-DITHIODIKETONES

Transition metal complexes derived from α-dithiodiketones have semiconducting properties comparable with large organic aromatic hydrocarbons and charge-transfer complexes. The observed resistivities lie between 103 and 1015 ohm cm (at 25°). They depend on the chelate structure, the metal, and the ligand substituents. For the square-planar complexes M(S2C2R2)2 M = Ni, Pd, and Pt, with the same substituents R, a linear correlation between the resistivity and the first polarographic half-wave potential was observed which indicates that electron transport takes place in the lowest unoccupied π MO's of the complexes. This is in accord with the proposed electronic structures of the complexes and the result of Hall-effect measurements which identify the majority charge carriers as negative. Measurements of the thermoelectric power coefficient, furthermore, revealed the presence of trapped negative centers of charge. Exposure of polycrystalline NiS4C4Ph4 to a 1.5-MeV electron beam produced a potential persisting for several weeks. Among the trigonal-prismatic complexes M(S2C2R2)3, the V, Cr, Mo, and W complexes have resistivities of between 1012 and 1014 ohm cm. The rhenium complexes are the best conductors of all, indicating that the unpaired electron must be in a molecular orbital delocalized over the whole molecular complex.