Abstract
The kinetics of complexation of activated octacyanomolybdate(IV) and octacyanotungstate(IV), generated by the absorption of a quantum of light with the aromatic heterocyclic ligand, pyrazine have been investigated. Each complex has a strong absorption band in the visible region which is assigned as a CTTL (charge-transfer to ligand) transition, being more pronounced in the [W(CN)8]4− system due to rapid deactivation, large back bonding stabilization energy and effective orbital mixing in the case of 5d orbitals with those of pyrazine. The CTTL transition leads to the substitution of pyrazine in 1:2 stoichiometry, showing pyrazine to behave as a unidentate ligand. On the basis of the decrease of rate constant and quantum yield values on increasing metal concentration, and the increase in value on increasing ligand and OH− concentration, an associative mechanism is proposed. In presence of excess of ligand, the observed rate law is:
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Ali, S.I., Majid, K. Photochemical kinetics and mechanism of the reaction of octacyanomolybdate(IV) and octacyanotungstate(IV) with pyrazine. Transition Metal Chemistry 22, 309–312 (1997). https://doi.org/10.1023/A:1018437129494
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DOI: https://doi.org/10.1023/A:1018437129494