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

Novel 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 R 2 SnClAmox ˙ 2H 2 O, R 3 SnClAmoxNa ˙ 2H 2 O and R 2 SnAmox 2 ˙ 2H 2 O (R = Me, Bu, Ph). The infrared spectra suggest that Amox − , in both R 2 SnClAmox ˙ 2H 2 O and R 2 SnAmox 2 ˙ 2H 2 O, behaves as a monoanionic bidentáte ligand, coordinating the tin(IV) atom through the ester‐type carboxylate, as well as through the lactamic carbonyl. In R 3 SnClAmoxNa ˙ 2H 2 O, 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 R 2 SnClAmox ˙ 2H 2 O and R 3 SnClAmoxNa ˙ 2H 2 O, trigonal bipyramidal configurations are proposed in the solid state, on the basis of infrared (IR) and Mössbauer spectroscopy, while in R 2 SnAmox 2 ˙ 2H 2 O 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 R 2 SnAmox 2 2H 2 O derivatives. 1 H and 13 C NMR measurements showed that both R 2 SnClAmox ˙ 2H 2 O and R 2 SnAmox 2 ˙ 2H 2 O are stable in DMSO‐d 6 solutions, maintaining their solid‐state configuration, while R 3 SnClAmoxNa ˙ 2H 2 O dissociates. Coordination hypotheses have been checked through the correlation between the Mössbauer isomer shift (δ) and the partial atomic charge on tin atoms ( Q Sn ) performed, for all the new organotin(IV) compounds, on the basis of an equalization procedure applied to idealized trigonal bipyramidal structures for R 2 SnClAmox ˙ 2H 2 O and R 3 SnClAmoxNa ˙ 2H 2 O and octahedral trans ‐R 2 for R 2 SnAmox 2 ˙ 2H 2 O.