Photosubstitution kinetics and mechanism of potassiumoctacyanomolybdate(lV) with 5- nitro-1, 10-phenanthroline

859-862The kinetics of thermal reaction of photochemically generated [Mo(CN)7(OH)]4 in basic medium and [Mo(CN)6(CNH)H2O]2 in acidic medium with 5-nitro-1 , 10-phenanthroline [nitrophen] has been studied in buffer solutions of pH 4.2 - 10.6 and ionic strength 8.0 x 10.2 M at 25 °C. The quantum yield for the formation of the photoproducts is found to depend upon the pH, ligand and [Mo(CN)8]4concentrations. The rate constants and quantum yield are smaller as compared to those of 1, 10- phenanthroline due to electron withdrawing effect of nitro group in nitrophen, which makes the latter a weaker ligand. The pseudo first order rate constants and quantum yield values in acidic medium are higher than those in basic medium. The mechanism of the photochemical substitution is different in two media. In acidic medium the reaction rate increases with increase in ligand concentration, while in basic medium, a variation in the ligand concentration does not lead to any marked change in the reaction rate. The reaction rate and the quantum yield are unaffected by the change in ionic strength