Preparation and structural studies on the Bu2Sn(IV) complexes with aromatic mono- and dicarboxylic acids containing hetero {N} donor atom

Nine complexes of ^tBu₂Sn(IV)²⁺ were obtained in the solid state with ligands containing -COOH group(s) and aromatic {N} donor atom. The binding sites of the ligands were identified by FT-IR spectroscopic measurements. It was found that in most cases the -COO⁻ groups are co-ordinated in monodentate manner. Nevertheless, in some of our complexes, the -COO⁻ group forms bridges between two central {Sn} atoms resulting in the formation of an oligomeric structure, a motif that is characteristic only to the nicotinate compound. These pieces of information and the rationalisation of the experimental ¹¹⁹Sn Mössbauer nuclear quadrupole splittings, Δ, - according to the point charge model formalism - support the formation of octahedral (O_h) or trigonal bipyramidal (TBP) molecular structures. The X-ray diffraction analysis of one complex obtained as single crystal revealed the distortion of the TBP geometry towards square pyramidal (SP) one. This was rationalised by PM3 molecular modelling of the ^tBu₂Sn(pdc) complex. In the asymmetric unit, the two chemically similar but symmetry independent molecules form pseudo-dimers, in which the Sn?Sn separation amounts to ca. 6.4 Å. The crystal lattice is stabilised by C-H?O hydrogen bonding between individual molecules.