Photochemistry and electronic spectroscopy of the Ru(SnPh3)(2)(CO)(2)(alpha-diimine) complexes: an ab initio investigation of the model system Ru(SnH3)(2)(Co)(2)(Me-DAB) (DAB=1,4-diaza-1,3-butadiene)

The low-lying excited states and associated potential energy curves of Ru(S nH3)(2)(CO)(2)- (Me-DAB), model system for the Ru(SnPh3)(2)(CO)(2)(alpha -d iimine) complexes, have been calculated at the complete active space SCF (C ASSCF) and complete active space perturbation theory second-order (CASPT2) levels, The experimental spectrum has been assigned without any ambiguity. A mechanism has been proposed for the Ru-Sn bond homolysis, process occurin g after irradiation of the title complex in the visible. The presence of a low-lying (SBLCT)-S-3 state with a pre-dissociative character is responsibl e for this primary reaction and for the long-lifetime emission observed wit h a low quantum yield. (C) 2001 Elsevier Science B.V. All rights reserved.