PHOTOSUBSTITUTION REACTIONS OF E)(1,4,8,11-TETRAAZACYCLOTETRADECANE)RUTHENIUM(II) COMPLEXES

Visible range photolyses of trans-[RuCl(cyclam)L](+) (cyclam = 1,4,8,1 1-tetraazacyclotetradecane; L = pyridine (py), 4-picoline (4-pic), iso nicotinamide (isn), or 4-acetylpyridine (4-acpy)) were studied in acid ic aqueous solution, and lead to exclusive azine photoaquation. The py and 4-pic complexes have a relatively high, and irradiation wavelengt h independent, quantum yield (0.020 < Phi < 0.025), while the isn and 4-acpy complexes have lower quantum yields (Phi(isn) approximate to 0. 006; Phi(4-acpy) < 0.001). The relative Phi s show patterns consistent with the excited-state tuning model proposed to explain the photochem istry of other related ruthenium(II) ammines. The results indicate tha t the excited-state precursor of the photochemistry should be a LF an d has a strong contribution from the d(z2) orbital, which should lie l ower in energy than the d(x2-y2). Accordingly, considering an approxim ate C-4v symmetry for the complexes, this LF should be a (3)E. The re sults also suggest that the intramolecular hydrogen bonds to the chlor ide that occur in the ground state may be still operative in the excit ed state in order to prevent the photoaquation of chloride.