Biomimetic trinuclear copper mixed-valence systems: electronic and magnetic parameters from ab initio calculations†

Abstract

A series of ab initio quantum chemistry calculations on a trinuclear mixed-valence system [(NH3)6Cu3O2]+3 has been performed in order to simultaneously evaluate its magnetic and electronic parameters, namely the magnetic coupling constants J 1 and J 2, the electron-transfer integrals t 1 and t 2, and the exchange-transfer terms h 1 and h 2. The procedure is based on the use of the effective Hamiltonian theory. The results evidence the presence of two ferromagnetic interactions in this compound, in good agreement with the behaviour found in the real system [L3Cu3O2]+3, where L = N-permethyl-(1R,2R)-cyclohexenediamine. Regarding electron-transfer terms, their values are about one order larger than the corresponding magnetic coupling constants, and essentially controlled by the direct interactions through the Cu d orbitals. The exchange-transfer terms are non-negligible, their amplitudes being similar to the J 1 constant.