PHOTOAQUATION OF CIS-BIS(AZINE)TETRAAMMINERUTHENIUM(II) COMPLEXES, CIS-RU(NH3)4(L)(L')N+1

Near-UV-visible range photolysis of cis-Ru(II)(NH3)4(L)2 (L = pyridine (py), 4-picoline (4-pic), isonicotinamide (isn), or 4-acetylpyridine (4-acpy)) and cis-Ru(II)(NH3)4(isn)(L) (L = py, 4-pic, pyrazine, or 4-acpy) leads to isn, L, and ammonia aquation. The complexes were irradiated at 313, 365, 405, 436, 480, and 519 nm, in acidic (pH 3.5-4.0) aqueous solution and with approximately 10(-3) M Ru complex concentration. The cis complexes have ligand field (LF) and metal-to-ligand charge-transfer (MLCT) states as the lowest energy excited states. The relative yields of the photoreactions of the cis complexes show patterns consistent with the excited-state "tuning" model proposed to explain photochemical properties of the pentaammine analogues, Ru(II)(NH3)5(L), which undergo photosubstitution when LF is the lowest energy excited state, as is also the case for the trans complexes. For each cis complex, a fixed ratio of released ligands is observed at all irradiation wavelengths studied, this being a strong evidence that the observed photoreactions occur from one single LF excited state, or an ensemble of equilibrated LF excited states of the same electronic configuration. Ligands are more easily labilized along the axis with the weaker pi-acceptor ability. For a particular axis, the ligand with lower pi-acceptor ability is more easily labilized.