New organotin(IV) ascorbates: synthesis, spectral characterization, biological and potentiometric studies

New organotin(IV) ascorbates of the general formulae R3Sn(HAsc) (where R=Me, n-Pr, n-Bu and Ph) and R2Sn(Asc) (where R=n-Bu and Ph) have been synthesized by the reaction of RnSnCl4−n (where n=2 or 3) with monosodium-l-ascorbate. The bonding and coordination behaviour in these complexes are discussed on the basis of UV-Vis, IR, Far-IR, 1H and 13C NMR, and 119Sn Mössbauer spectroscopic studies. l-Ascorbic acid acts as a monoanionic bidentate ligand in R3Sn(HAsc) coordinating through O(1) and O(3). The Mössbauer studies together with IR and NMR studies suggest that for these polymeric derivatives, the polyhedron is trigonal bipyramidal around tin with three organic groups in the equatorial positions. In R2Sn(Asc), l-ascorbic acid acts as dianionic tetradentate ligand and a polymeric structure with octahedral geometry around tin with trans organic groups has been tentatively proposed. The complexes have been assayed for their anti-inflammatory and cardiovascular activity. Ph2Sn(Asc) has been found to show the highest activity among the studied complexes. It is suggested on the basis of potentiometric studies of Me2Sn(IV) and Me3Sn(IV) systems with l-ascorbic acid that under physiological conditions (pH=7.0) Me2Sn(HAsc)(OH) (∼60%), Me2Sn(OH)2 (∼40%) and Me3Sn(HAsc) (∼60%), Me3Sn(OH) (∼40%), respectively, are existing, which may be responsible for their biological activities.