Kinetics and mechanism of the photochemical reaction of Octacyanomolybdate (IV) and Diethylenetriamine

Photolysis of Mo(CN)₈]⁴⁻ in the presence of diethylenetriamine (dien) leads to the complexation of ligand via hydrogen in the stoichiometry 2:1. The mechanism of the complexation was investigated by spectroscopy absorption and the rate constants and the quantum yield determined. Rate constants and quantum yields for the formation of the final products were found to depend on pH, ligand, and metal cyanide concentration. The values are a maximum at pH 7.4. At pH >7.4 the reverse reaction, generating octacyanomolybdate complex from the heptacyano species, is faster. At low pH, the ligand is protonated and less reactive; hence, the rate of reaction and quantum yield values decrease. The ionic strength does not affect the reaction rate, implying an associative mechanism for the photochemical reaction with dien, supported by the rate law. The observed rate law is: © 1999 John Wiley & Sons, Inc. J Chem Kinet 31: 89–93, 1999