Formation and dissociation of the ethylenediaminetetra-acetic acid complex of the molybdenum(V) dimer Mo2O42+ in aqueous perchloric acid solution

Abstract

The kinetics of the equilibration of the molybdenum(V,V) complexes Mo₂O₄²⁺(A) and Mo₂O₄Y^2–(B) in the presence of excess of EDTA (H₄Y = ethylenediaminetetra-acetic acid) have been studied by conventional spectrophotometry at 25°, I= 2·0M(LiClO₄). At constant hydrogen-ion concentrations in the range [H⁺]= 0·5–2·0M investigated, first-order rate constants K_eq may be expressed as Keq =a[EDTA]+b. The hydrogen-ion dependences of a and b, corresponding to the formation and dissociation processes respectively are not simple. For the dissociation process the equation b=b₁[H⁺]⁴/(l +b₂[H⁺]³) gives a good fit to the experimental data. Contributions from terms in [H⁺] and [H⁺]² in the denominator cannot be ruled out however. An inverse hydrogen-ion dependence is apparent for a but the precise form of this is less certain.