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

The 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-ni tro-1, 10-phenanthroline [nitrophen] has been studied in buffer solutions o f pH 4.2 - 10.6 and ionic strength 8.0 x 10(-2) M at 25 degreesC. The quant um yield for the formation of the photoproducts is found to depend upon the pH, ligand and [Mo(CN)(8)](4) concentrations. The rate constants and quant um yield are smaller as compared to those of 1,10-phenanthroline due to ele ctron withdrawing effect of nitro group in nitrophen, which makes the latte r a weaker ligand. The pseudo first order rate constants and quantum yield values in acidic medium are higher than those in basic medium. The mechanis m of the photochemical substitution is different in two media. In acidic me dium the reaction rate increases with increase in ligand concentration, whi le in basic medium, a variation in the ligand concentration does not lead t o any marked change in the reaction rate. The reaction rate and the quantum yield are unaffected by the change in ionic strength.