Formation and dissociation of the ethylenediaminetetra-acetic acid complex of the molybdenum(V) dimer Mo2O4 2+ in aqueous perchloric acid solution

The kinetics of the equilibration of the molybdenum(V,V) complexes Mo2O42+(A) and Mo2O4Y2–(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 Keq 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.