Enhancement of hydrolysis through the formation of mixed heterometal species: Al3+/CH3Sn3+ mixtures

The hydrolysis of mixed-metal cations (Al3+/CH 3Sn3+) was studied in aqueous solutions of NaNO 3, at I = 1.00 ± 0.05 mol·dm-3 and T = 298.15 K, by potentiometric technique. Several hydrolytic mixed species are formed in this mixed system, namely, Alp(CH3Sn) q(OH)r with (p, q, r) = (1, 1, 4), (1, 1, 5), (1, 1, 6), (2, 1, 4), (1, 2, 5), (1, 4, 11), (1, 3, 8), and (7, 6, 32). The stability of these species, expressed by the equilibrium: pAl3+ + qCH 3Sn3+ + rOH- = Alp(CH 3Sn)q(OH)r 3(p+q)-r, βpqr OH, can be modeled by the empirical relationship: log βpqr OH = -3.34 + 2.67p + 9.23(q + r). By using the equilibrium constant Xpqr relative to the formation reaction: pAl(p+q)(OH) r + q(CH3Sn)(p+q)(OH)r = (p + q)Alp(CH3Sn)q(OH)r, it was found that the formation of heterometal mixed species is thermodynamically favored, and the extra stability can be expressed as a function of the difference in the stability of parent homometal species. This leads, in turn, to a significant enhancement of hydrolysis and solubility.