Solvent effects on complexation of molybdenum(VI) with nitrilotriacetic acid in different aqueous solutions of methanol

The formation constants of the species formed in the systems H+ + Mo(VI) + nitrilotriacetic acid and H+ + nitrilotriacetic acid have been determined in different aqueous solutions of methanol at 25 °C and constant ionic strength 0.1 mol dm− 3 sodium perchlorate, using spectrophotometric and potentiometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with nitrilotriacetic acid of the type MoO3L− 3 at − log[H+] = 5.8. The formation constant in various media was analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlations of the formation constant, KS, versus α (hydrogen-bond donor acidity) and π* (dipolarity/polarizability) are poor in all solutions, except for β (hydrogen-bond acceptor basicity), but multi-parameter correlations represent significant improvement with regard to the single-parameter models. Linear relationship is observed when the experimental log KS is plotted versus the calculated ones, while all the Kamlet and Taft's parameters are considered. Finally, the results are discussed in terms of the effect of solvent on complexation.