Modulation of redox potentials utilizing the flexible coordination sphere of a penta-coordinate complex in the solid state

Abstract

Slight changes in the coordination structure of the manganese(V)-nitrido anionic complex, [Mn^V(N)(CN)₄]²⁻, induced by using a “lipid package” approach markedly made an impact on the corresponding redox potentials. The single crystals of four lipid assemblies, [dabco-(CH₂)_n−1-CH₃]₂[Mn(N)(CN)₄(H₂O)]·xH₂O (n = 15, 16, 17 and 18; dabco = 1,4-diazabicyclo[2,2,2]octane), were synthesized and solid-state cyclic voltammetric studies demonstrated that the [Mn^V(N)(CN)₄]²⁻ anions with smaller “cross” NC–Mn–CN bond angles exhibit higher redox potentials. The observed trend reflects the energy change associated with the structural transformation from [Mn^V(N)(CN)₄]²⁻ to [Mn^VI(N)(CN)₄]²⁻ and is supported by the results of DFT calculations. The NC–Mn–CN bond angles in the flexible [Mn(N)(CN)₄]²⁻ structure exhibit excellent correlation with the redox potentials of the complexes in the solid state.