VOLTAMMETRIC AND POTENTIOMETRIC STUDIES ON THE STABILITY OF VANADIUM(IV) COMPLEXES - A COMPARISON OF SOLUTION-PHASE VOLTAMMETRY WITH THE VOLTAMMETRY OF MICROCRYSTALLINE SOLID COMPOUNDS

Formal potentials of non-oxo vanadium complexes obtained by the cyclic voltammetry of solutions and of solid microcrystalline compounds are compared with potentiometrically determined stability constants of the corresponding oxovanadium(IV) complexes. The stability constants show a qualitative correlation with the formal potentials. The non-oxo com plexes exhibit a reversible one-electron system V-IV/V-III as well as V-IV/V-V in dichloromethane solution whereas the oxo complexes only sh ow the transition between V-IV and VV. Generally, the oxidation of non -oxo vanadium(IV) complexes proceeds at higher potentials than that of the corresponding oxovanadium(IV) species. The shift of the formal po tentials is clearly correlated with the structure of the compounds.