Redox potentials of a series of bis(2,4-pentanedionato)cobalt(III) complexes containing amine, phosphine, arsine, or their hybrid donor didentate ligands. σ and π contributions in the Co^III-N, -P and -As bonding

Reduction (E_1/2(red)) and oxidation potentials (E_1/2(ox)) of [Co(acac)₂(L)]⁺ (acac=2,4-pentanedionate) complexes containing an N-N, N-N′, N′-N′, N-P, P-P, N-As, or As-As′ didentate ligand as L(N = -CH₂NH₂; N′ = -CH₂NMe₂; P = -CH₂PMe₂; As′ = -CH₂AsMe₂; As′ = -CH₂CH₂AsMe₂) were determined by electrochemical measurements. The E_1/2(red) values which reflect the dσ*(Co) orbital (homo) energy shift negatively in the following order: (i) L = N′-N′ > N′-N > N-N; (ii) L = N′-N > As-N > P-N; and (iii) L = N′-N′ > As-As′ > P-P. The E_1/2(ox) values shift positively in the following order : L = P-P, As-As′ < P-N, As-N < N-N, N-N′, N′-N′. This order suggests that the dπ(Co) orbital is more destabilized by the phosphine or arsine ligands than the amine ones.