Interaction of alkyltin(IV) compounds with ligands of interest in the speciation of natural fluids: Carboxylate and hydroxycarboxylate complexes of monomethyltin(IV) trichloride

The formation and stability of some carboxylate and hydroxycarboxylate (acetate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate, malate and citrate) complexes of monomethyltin trichloride was studied potentiometrically at 25degreesC and at different ionic strengths in NaNO(3) aqueous solution, The following quite stable species are formed in the different systems (M = CH(3)Sn(3+)): ML(OH)(+), ML(2)(OH)(o), ML(OH)(2)(o) and M(2)L(OH)(5)(o) for acetate; MLH(o), ML(-), ML(OH)(2-) and ML(OH)(2)(3-) for propanetricarboxylate; MLH(2)(+), MLH(o), ML(-), ML(OH)(2-) and ML(OH)(2)(3-) for butanetetracarboxylate; ML(OH)(o), ML(OH)(2)(-) and ML(OH)(3)(2-), for malate; ML(o), ML(OH)(-), ML(OH)(2)(2-) and ML(OH)(3)(3-) for citrate. Hydroxycarboxylate complexes are significantly stronger than simple carboxylate ones and this is likely to be due to the interaction of the -OH group in citrate and malate with monomethyltin(IV), whose strength was also quantified. It was found that the stability of these complexes can be roughly expressed by the simple relationship logK = a xi, where xi is the product of the charges of reactants and logK is the equilibrium constant, For simple carboxylic ligands we have a = 1.8+/-0.4 and, for hydroxycarboxylic ligands, a = 3.7+/-0.9. Other useful empirical relationships are reported,, Moreover, hydroxycarboxylic complexes also play a prominent role in the speciation of monomethyltin(IV) under the pH conditions of interest for natural fluids.