Organometallic complexes with biological molecules, IV. Di‐ and tri‐organotin(IV) amoxicillin derivatives: Solid‐state and solution‐phase spectroscopic investigations

Abstract

AbstractNovel di‐ and tri‐organotin(IV) derivatives of amoxicillin (amoxicillin− = Amox− = 6‐[D(‐)‐ß‐ amino ‐ p ‐ hydroxyphenylacetamido]penicillinate) have been prepared. The isolated compounds showed stoichiometries of the type R2SnClAmox ˙ 2H2O, R3SnClAmoxNa ˙ 2H2O and R2SnAmox2 ˙ 2H2O (R = Me, Bu, Ph). The infrared spectra suggest that Amox−, in both R2SnClAmox ˙ 2H2O and R2SnAmox2 ˙ 2H2O, behaves as a monoanionic bidentáte ligand, coordinating the tin(IV) atom through the ester‐type carboxylate, as well as through the lactamic carbonyl.In R3SnClAmoxNa ˙ 2H2O, Amox− coordinates the organotin(IV) moieties through the lactamic carbonyl. In all of the compounds, water molecules are not involved in coordination, as inferred by thermogravimetric (TG) investigation. In both R2SnClAmox ˙ 2H2O and R3SnClAmoxNa ˙ 2H2O, trigonal bipyramidal configurations are proposed in the solid state, on the basis of infrared (IR) and Mössbauer spectroscopy, while in R2SnAmox2 ˙ 2H2O the coordination geometry at tin could be a skew‐trapezoidal bipyramid, with two chelating amoxicillin residues which act as bidentate ligands in the trapezoidal plane, and with the organic groups in axial positions. The CSnC angles calculated from the experimental Mössbauer quadrupole splitting predict a bent skeleton in all the R2SnAmox2 2H2O derivatives. 1H and 13C NMR measurements showed that both R2SnClAmox ˙ 2H2O and R2SnAmox2 ˙ 2H2O are stable in DMSO‐d6 solutions, maintaining their solid‐state configuration, while R3SnClAmoxNa ˙ 2H2O dissociates.Coordination hypotheses have been checked through the correlation between the Mössbauer isomer shift (δ) and the partial atomic charge on tin atoms (QSn) performed, for all the new organotin(IV) compounds, on the basis of an equalization procedure applied to idealized trigonal bipyramidal structures for R2SnClAmox ˙ 2H2O and R3SnClAmoxNa ˙ 2H2O and octahedral trans‐R2 for R2SnAmox2 ˙ 2H2O.