Synthetic, Spectroscopic, Crystallographic, and Biological Studies of Seven-Coordinated Diorganotin(iv) Complexes Derived from Schiff Bases and Pyridinic Carboxylic Acids

The synthesis and characterisation of diorganotin(iv) monomeric derivatives of pyridine Schiff bases and pyridinic carboxylic acids are reported. All complexes were characterised by mass spectrometry, elemental analyses, IR spectra, and multinuclear NMR analyses. Among them, complexes 5a, 5d, 5e, 5g, and 6a were also confirmed by X-ray crystallography diffraction analyses, which led to establishing that the tin atom is seven-coordinated and has a distorted pentagonal–bipyramidal coordination environment in the solid state and also revealed that both ligands occupy the equatorial positions and the organic substituents the axial positions. The antioxidant activity of the synthetic derivatives towards 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) as well as the thiobarbituric acid reactive substances (TBARS) assay were determined, and were compared with standard antioxidants, showing a dose-dependent activity in both cases. A prominent response was obtained depending on the substituent. The anti-inflammatory activity was also evaluated on a 12-O-tetradecanoylphorbol-13-acetate (TPA) model of induced acute inflammation. The results of the biological tests are discussed in terms of structural characteristics.