Synthesis, characterization, and in vitro antimicrobial activity of organotin(IV) complexes with triazolo-pyrimidine ligands containing exocyclic oxygen atoms.

Tri-organotin(IV) complexes of the triazolo-pyrimidine derivatives 4,5-dihydro-5-oxo-[1,2,4]triazolo-[1,5a]pyrimidine (5HtpO), 4,7-dihydro-5-methyl-7-oxo-[1,2,4]triazolo-[1,5a]pyrimidine (HmtpO), and 4,5,6,7-tetrahydro-5,7-dioxo-[1,2,4]triazolo-[1,5a]pyrimidine (H2tpO2), and the diorganotin derivative n-Bu2Sn(tpO2), were synthesized and characterized by means of infrared and 119Sn Mo¨ssbauer spectroscopy. In all the complexes obtained the triazolopyrimidines act as multidentate ligands producing polymeric structures. A trigonal bipyramidal arrangement of the ligands around the tin atom is proposed for triorganotin(IV) derivatives, with organic groups on the equatorial plane and bridging anionic ligands. DFT calculations were performed on the structure of H2tpO2 and on its mono- an di-anions, to investigate their harmonic vibrational modes. The observed trend of the experimental and calculated carbonyl stretching frequencies furnishes a support for the interpretation of the structure of the organotin(IV) complexes obtained with this ligand. The structure of n-Bu2Sn(tpO2) was elucidated by quantum chemical calculations, performed on a model system of the polymeric complex by a two layers ONIOM method. The combined experimental and theoretical results obtained support for a trans-n-Bu2 distorted octahedral geometry, with the tpO2 2 units acting as bis-chelate ligands bridging the diorganotin(IV) moieties, and with the N(1)O(7) and N(4)O(5) chelating groups in the equatorial plane showing a cis-O2, or cis-N2, coordination. In vitro antimicrobial tests were performed on n-Bu3Sn(HtpO2) and Ph3Sn(HtpO2), and a good antifungal and antibiofilm activity was observed, in particular for n-Bu3Sn(HtpO2).