STABILIZATION OF HIGH OXIDATION-STATES IN TRANSITION-METALS - AN ELECTROCHEMICAL AND COMPUTATIONAL STUDY OF STRUCTURALLY COMPARABLE MOLYBDENUM AND TUNGSTEN COMPLEXES

Molybdenum and tungsten chlorides, chloride oxides and chloride nitrid es as well as thiazene and phosphazene metallacycles were studied by e lectrochemical methods in CH2Cl2. The different ligand systems have a profound influence on the redox potentials. The stabilization of high valency increases from the hexachloro to pentachlorooxo to chloronitri do complexes and the metallacycles. There is a systematic difference i n the electrode potentials between molybdenum and tungsten redox coupl es. The geometries of the d(1) and d(0) species, optimized using densi ty functional methods, are in good agreement with the available experi mental data and trends in redox data are reproduced by the computed en ergy difference between the appropriate d(1)/d(0) pair. The relative s tability of the higher oxidation state is directly linked to the donor properties of the ligands present, and increases in the order: Cl-6 < F-6 < Cl5O < Cl-4(N3S2) < Cl-N?3P?2 < Cl4N.