Photo-initiated substitution kinetics in the complexes of octacyanomolybdate(lV) and octacyanotungstate(IV) with triethanolamine

Abstract

The photochemical reactivity of octacyano complexes of Mo(IV) and W(IV) with tertiary aminoalcohols has been studied. The reaction occurs in 1:3 stoichiometry. Irradiation of aqueous solutions of metal cyanides in the range of occurrence of d-d bands of the ligand field leads to the formation of the primary photoproduct where a CN^- ion is replaced by OH^-, which undergoes subsequent thermal substitution by entering ligand (TEOA). Transitions in the case of W(IV) are found to be more pronounced than those in Mo(IV). Photochemical reactivity is observed to increase with increase in the concentration of ethanolic group. The rate of the reaction and quantum yield increase with increase in ligand concentration and decrease with increase in [M(CN)₈]^4- concentration. An associative mechanism is proposed to explain the observed data. In presence of excess of ligand, the observed rate law is: <em>K</em>_obs=<em>k</em>₂<em>k</em>₄<em>l</em>_a[OH^-][TEOA]/1+<em>k</em>₂[OH^-]