Novel di-and tri-organotin(1V) derivatives of amoxicillin (amoxicillin-= Amox-= 6-[D( -)-/?aminophydroxyphenylacetamido]penicillinate)
have been prepared. The isolated compounds showed stoichiometries of the type R,SnCIAmox * 2H,O, R,SnCIAmoxNa. 2H20 and R,SnAmox,. 2H,O (R=Me, Bu, Ph). The infrared spectra suggest that Amox-, in both R,SnCIAmox * 2H20 and R2SnAmox,. 2H,O, behaves as a monoanionic bidentate ligand, coordinating the tin(1V) atom through the ester-type carboxylate, as well as through the lactamic carbonyl.
In R,SnCIAmoxNa . 2H20, Amox-coordinates the organotin(1V) 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,SnCIAmox. 2H20 and R,SnCIAmoxNa .2H,O, trigonal bipyramidal configurations are proposed in the solid state, on the basis of infrared (IR) and Mossbauer spectroscopy, while in R,SnAmox2 . 2H20 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 -S n -C angles calculated from the experimental Mossbauer quadrupole splitting predict a bent skeleton in all the R2SnAmox2 2H20 derivatives. 'H and ' ,C NMR measurements showed that both R,SnCIAmox * 2H20 and R,SnAmox, . 2H20 are stable in DMSO-d, solutions, maintaining their solid-state configuration, while R,SnCIAmoxNa . 2H20 dissociates.
Coordination hypotheses have been checked through the correlation between the Mossbauer isomer shift (6) and the partial atomic charge on tin atoms (Qs.) performed, for all the new organo-Author to whom correspondence should be addressed. tin(1V) compounds, on the basis of an equalization procedure applied to idealized trigonal bipyramidal structures for R2SnCIAmox 2H20 and R,SnCIAmoxNa . 2H20 and octahedral trans-R, for R2SnAmox2. 2H20.