Photochemical reactions of pentaammine(cyanopyridine)ruthenium(II) complexes, [RU(NH3)(5)L](2+)

Photolyses of nitrile bonded [Ru(NH3)(5)L](2+) complexes (L = 2-cyanopyridi ne (2-NCpy); 3-cyanopyridine (3-NCpy); or 4-cyanopytidine (4-NCpy)) at 365, 404, and 436 nm, were studied in aqueous solution, and lead exclusively to ammonia and cyanopyridine photoaquation. No linkage isomerization to yield the pyridinyl bonded complexes occurs, suggesting that the kinetic control observed for thermal reactions of Ru(II) ammines with nitriles are also op erative for the possible transients and intermediates formed following deac tivation of the excited states. Ligands photoaquation showed irradiation wa velength independent quantum yields. The 2-NCpy and 3-NCpy complexes have h igher L quantum yields and the 4-NCpy have higher ammonia quantum yield. In itial excitation in the (MLCT)-M-1 (metal to ligand charge transfer) energy range, is followed by competitive internal conversion and intersystem cros sing to one (LF)-L-3 (ligand field) state or one (LF)-L-3 manifold of excit ed states of the same configuration, and of lowest energies, from which pho toaquation occurs. The results suggest that these states for 2-NCpy and 3-N Cpy complexes have more contribution from the z(2) orbital, while for 4-NCp y the x(2) - y(2) have larger contribution. (C) 1999 Elsevier Science S.A. All rights reserved.