Preparation and structural studies on dibutyltin(IV) complexes with pyridine mono- and dicarboxylic acids.

A number of organotin(IV) complexes with pyridine mono- and dicarboxylic acids (containing ligating -COOH group(s) and aromatic {N} atoms) were prepared in the solid state. The bonding sites of the ligands were determined by means of FT-IR spectroscopic measurements. It was found that in most cases the -COO- groups form bridges between two central {Sn} atoms, thereby leading to polymeric (oligomeric) complexes. On this basis, the experimental Sn-119 Mossbauer spectroscopic data were treated with partial quadrupole splitting approximations. The calculations predicted the existence of complexes with octahedral (oh) and trigonal-bipyramidal (tbp) structures, but the formation of complexes with pentagonal-bipyramidal (pbp) structures could not be ruled out. Single-crystals of 2-picolinic and pyridine-2,6-dicarboxylic acid Bu2Sn(IV)(2+) complexes were obtained. The X-ray diffraction studies revealed that the central {Sn} atoms are in a pbp environment with bond distances characteristic of organotin(IV) compounds. The two butyl groups are located in axial positions. Sn-119 NMR measurements in dmso solution and in the solid state indicated that the polymeric structures of the complexes are not retained in solution. The results of the solid-state Sn-119 NMR measurements for compounds 1a, 2a and 6a are in agreement with the structures predicted by Mossbauer spectroscopy and revealed by X-ray diffraction.