Electron transfer in authentic triangular copper(II) trimers with Cu₃X (X = oxygen or hydroxy) core. The Cu^II₂Cu^III-Cu^II₃ and Cu^II₃-CuCu^ICu^II₂ couples

Abstract

Trinuclear triangular copper(II) complexes of pyridine•2-carbaldoxime (HPL) and isonitrosoketimine ligands of type RNC(R(R')C(R')NOH (R = Et, n-Pr, n-Bu, Ph; R'=Me. Ph) have been examined electrochemically. These strongly antiferromagnetic complexes are of types (Cu₃0(ligand)₃)⁺ and [Cu₃OH(ligand)²⁺, having Cu₃0 and Cu₃0H cores, respectively. The known structure of [Cu₃OH(PL)₃]²⁺ provides an authentic reference point for data analysts. Cyclic voltammetry and constant-potential electrolysis (platinum working electrode) show that complexes with a Cu₃0 ooze uniformly display a one-electron-transfer process characterized by the oxidation-state description Cu^IIICu^II+e^-⇌ Cu^II₃ with E°₂₉₈ in the range 0.3-0.6 V vs. SCE in acetonitrile and dimethylformamide. The species with a Cu3OH core do not have this electrochemical response. On the other hand, such species show a novel one-electron-transfer process of the type Cu^II₃+e^-⇌ Cu^II₂Cu^I with E°₂₉₈ in the range -0.3 to -0.45 V vs. SCE at a hanging-mercury-drop electrode in acetonitrile. The Cu₃0 core does not display this process. In effect the electrochemical behaviors of the two cores are complementary: the Cu₃O core undergoes oxidation while the Cu₃OH core undergoes reduction. Thus the core proton acts in a va/velike fashion in controlling the direction of electron transfer Addition of an acid (HCl0₄) converts the Cu₃O species to the Cu₃OH species. Conversely, addition of a base (NEt₃) converts Cu₃OH to Cu30. The electrochemical responses change accordingly with addition of acid or base The interconversion reactions are also useful at preparative levels.