Solvent Effects on Complexation of Dioxovanadium(V) with Penicillamine in Methanol−Water Mixtures

The formation constants of the species formed in the systems H+ + dioxovanadium(V) + penicillamine and H+ + penicillamine have been determined in aqueous solutions of methanol at 25 °C and constant ionic strength, using spectrophotometric and potentiometric techniques. It was shown that dioxovanadium(V) forms two mononuclear 1:1 and 1:2 complexes with penicillamine. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, β121 and β142, versus α (hydrogen-bond donor acidity) and β (hydrogen-bond acceptor basicity) is poor in all solutions, except for π* (dipolarity/polarizability), but multiparameter correlation represents significant improvement with regard to the single-parameter models. Linear relationships are observed when log β121 and log β142 are plotted versus π*. Finally, the results are discussed in terms of the effect of the solvent on complexation.

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