Experimental evidence of the disproportionation equilibrium in copper mixed-valence complexes

Abstract

Experimental evidence for a dismutation equilibrium in the mixed-valence (MV) [Mn+ -M(n+1)+] system type has been elusive and its existence can be established only when the oxidation-reduction processes involved are reversible. Previous research in the field of binuclear Cu(II)-Cu(II), Cu(I)-Cu(I) and the related MV Cu(II)-Cu(I) complexes allowed us to obtain electrochemical evidence for the disproportionation equilibrium in some of these systems. In this communication we report discuss experiments with [(RCOO)2Cu(II)-Cu(I)(OOCR)2]- (R = CH3, Ph) type MV complexes that give direct non-electrochemical experimental evidence for the presence in solution of the disproportion equilibrium: 2[(R-COO)2Cu(II)-Cu(I)(OOC-R)2]-⇔ (R-COO)4Cu2(II) + [(RCOO)4Cu(I)2]2- It was possible to isolate the different components of the disproportionation equilibrium by varying temperature and solvent conditions. To our knowledge, this is the first non-electrochemical experimental evidence of this equilibrium fo