Photoexcitation of the potassium octacyanotungstate(IV)· 5–nitro-1,10–phenanthroline system: kinetics and mechanism of the reaction

The kinetics of thermal reactions of the photochemically-generated species W(CN)7OH]4− and W(CN)6–(CNH)(H2O)]2− with 5–nitro-1,10–phenanthroline (nitrophen) in basic and acidic media, respectively, were studied in buffer solutions at pH 4.2–10.6 and ionic strength 7.5×10−2kg−1 at 20°C. The quantum yield for the formation of the photoproduct was calculated and found to depend upon pH and the ligand and W(CN)8]4− concentrations. The rate constants and quantum yields were less compared with 1,10–phenanthroline due to the electron-withdrawing inductive effect of the nitro group in nitrophen, which makes the latter a weaker ligand. The pseudo-first-order rate constant and quantum yield values in acidic media are higher than in basic media and the mechanisms of the photochemical substitution are different in the two media. This revised version was published online in June 2006 with corrections to the Cover Date.