Potentiometric, ¹H NMR and ESI-MS investigation on dimethyltin(IV) cation–mercaptocarboxylate interaction in aqueous solution

The interaction between dimethyltin(IV) cation with three different mercaptocarboxylic acids (thiolactic, 3-mercaptopropanoic and thiomalic acids) was studied in aqueous solution by potentiometry, ¹H NMR spectroscopy and electrospray (ESI) mass spectrometry. The speciation model and equilibrium data were determined on the basis of potentiometric evidences, as well as the bonding sites by means of ESI mass spectrometry and the geometry of the species by ¹H NMR spectroscopy. The speciation profiles show the formation of different complex species, whose stabilities and formation percentages, in particular for the mononuclear mixed species, are high in a wide pH range. ESI mass spectrometry studies together with ¹H NMR investigations fully confirm the speciation model. The former also allows to propose a cyclic structure with O→Sn and S→Sn coordination, confirmed by MS/MS analysis; the latter indicates angles mostly matching with a Tbp arrangement around the metal.