PHOTOEXCITATION OF THE POTASSIUM UNGSTATE(IV)CENTER-DOT-5-NITRO-1,10-PHENANTHROLINE SYSTEM - KINETICS AND MECHANISM OF THE REACTION

The kinetics of thermal reactions of the photochemically-generated spe cies [W(CN)(7)OH](4-) and [W(CN)(6)(CNH)(H2O)](2-) with 5-nitro-1,10-p henanthroline (nitrophen) in basic and acidic media, respectively, wer e studied in buffer solutions at pH 4.2-10.6 and ionic strength 7.5 X 10(-2) kg(-1) at 20 degrees C. The quantum yield for the formation of the photoproduct was calculated and found to depend upon pH and the li gand and [W(CN)(8)](4-) concentrations. The rate constants and quantum yields were less compared with 1,10-phenanthroline due to the electro n-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 med ia and the mechanisms of the photochemical substitution are different in the two media.