Coexistence of two thermally induced intramolecular electron transfer processes in a series of metal complexes [M(Cat-N-BQ)(Cat-N-SQ)]/ [M(Cat-N-BQ)<inf>2</inf>] (M = Co, Fe, and Ni) bearing non-innocent catechol-based ligands: A combined experimental and theoretical study

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat-NBQ)(Cat-N-SQ)]/ [M(Cat-N-BQ)2], for which M = Co (2), Fe (3) and Ni(4), and Cat-N-BQ and Cat-N-SQ denote the mononegative (Cat-N-BQ) or dinegative (Cat-N-SQ 2-) radical forms of the tridentate Schiff-base ligand 3,5-diterf-butyl-1,2-quinone-l-(2-hydroxy-3,5di-tert-butylphenyl)imine, have been studied by variable-temperature UV/ Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2 has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand-to-metal (IET LM) and ligand-to-ligand (IETLL). IETLL was only found to take place in complex 3, and no IET was observed for complex 4. Such experimental studies have been combined with ab initio wavefunction-based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitais and to access the ground states and excited-spin states, as well as charge-transfer states giving additional information on the different IET processes. © 2010 Wiley-VCH Verlag GmbH & Cu. KGaA, Weinheim.