Synthesis, characterization, crystal structures and anti-diabetic activity of organotin (IV) complexes with 2-(4-hydroxynaphthylazo)-benzoic acid

Abstract

Three new organotin(IV) complexes 1–3 were synthesized by the reaction of 2-(4-hydroxynaphthylazo)-benzoic acid with bis-tributyltin(IV) oxide (1), dibutyltin(IV) oxide (3) or trimethyltin(IV) chloride (2), respectively. The complete characterization of the complexes was accomplished by elemental analysis, IR and multinuclear [1H- and 13C- and 119Sn-] NMR spectroscopy. The crystal structures of all the complexes were elucidated with the help of X-ray single crystal diffraction analysis. The geometry around tin atoms in 1 and 2 was trigonal bipyramidal geometry where the equatorial plane was occupied by the three alkyl groups (Bu or Me) and the axial positions in 1 were being occupied by carboxylate and phenoxide oxygen atoms giving rise to a polymeric structure. In 2, a hydroxy oxygen atom bridges two tin atoms occupying axial position while the other axial positions in each tin atom were being occupied by a carboxylate oxygen atom or oxygen atom of a water molecule respectively thereby completing trigonal bipyramidal geometry. The structure of 3 was a di-nuclear complex with six-coordinate distorted skew trapezoidal and seven-coordinate pentagonal bipyramidal geometry around the tin atoms, respectively. In the dinuclear structure, one of the tin atoms is coordinated by a terminal azo-ligand while the other tin atom is coordinated by two terminal azo-ligands. In addition to this, another azo-carboxylate ligand bridges the two atoms in the dinuclear structure. The NMR study showed that in the solution the complexes 1 and 2 adopted four-coordinate geometry, while in 3 there is five-coordinate structure. Complexes 1 and 3 were screened for their antidiabetic activities against α-glucosidase enzyme and results of the assay found that compound 3 exhibited significant inhibition activity.