Thermodynamic and spectroscopic study of the binding of dimethyltin(IV) by citrate at 25°C

Thermodynamic (potentiometric and calorimetric) and spectroscopic ((1)H NMR, (119)Sn Mossbauer) studies were performed in aqueous solution in order to characterize the interaction of dimethyltin(IV) cation with citrate ligand. Six species {(CH(3))(2)Sn(cit)(-); [(CH(3))(2)Sn](2)(cit)(2)(2-); (CH(3))(2)Sn(cit)H(0); (CH(3))(2)Sn(cit)OH(2-); [(CH(3))(2)Sn](2)(cit)OH(0); [(CH(3))(2)Sn](2)(cit)(OH)(2)(-)} were found. All the species formed in this system are quite stable and formation percentages are fairly high. For example, at pH = 7.5 and C(CH(3))(2)Sn = C(cit) = 10 mmol l(-1), Sigma% for [(CH(3))(2)Sn](2)(cit)(OH)(2)(-) and (CH(3))(2)Sn(cit)OH(2-) species reaches 65%. Overall thermodynamic parameters obtained show that the main contribution to stability is entropic in nature. Thermodynamic parameters were discussed in comparison with a simple tricarboxylate ligand (1,2,3-propanetricarboxylate). Two empirical relationships were derived from thermodynamic formation parameters. Spectroscopic results fully confirm the speciation model defined potentioinetrically and show the mononuclear species to have an eq-(CH(3))(2)Tbp structure with different arrangements around the metal, while for [(CH(3))(2)Sn](2)(cit)(OH)(2)(-) there are two different Sn(IV) environments, namely trans-(CH(3))(2) octahedral and cis-(CH(3))(2) Thp. Copyright (c) 2006 John Wiley & Sons, Ltd.