EPR studies of X-ray irradiated dithiophosphate metal complexes

Different metal O,O’-disubstituted dithiophosphates have been studied by Electron Paramagnetic Resonance (EPR) spectroscopy after X-ray irradiation at 77K. Formation of different radicals has been recorded depending on the central metal atom and on the substituents in the ligands. Phosphorus-centered radicals with hyperfine constants of about 800 G were recorded after radiolysis of zinc and cadmium complexes. Their shape and EPR parameters lead to their identification as phosphoranyl radicals (RO)₂P (S)S^?. In these compounds two different types of coordination of the ligands have been found by X-ray analysis. One dithiophosphate group is coordinated to the metal atom forming a chelate four-membered ring, and another one is a bridging group. The formation of phosphorus-centered radicals is related to the presence of a bridging, or interchelating group. In other metal dithiophosphates, with only chelating groups present, such radicals were not found. In platinum, palladium and nickel dithiophosphates similar EPR signals with small hyperfine coupling were observed. They have been identified as carbon-centered radicals with one phosphorus in γ-position.