Synthesis, spectroscopic (Mössbauer, IR and NMR) and X-ray structural studies of diorganotin complexes of 2,2′-bipyrimidine and further NMR studies of diorganotin-pyrazine and — 2,2′-azopyridine complexes

Abstract

The ligand 2,2′-bipyrimidine (bipym) was reacted with diorganotins R 2SnCl 2 (R = methyl, ethyl) and complexes of the types R 2SnCl 2 bipym, R 2SnCl 2 bipym · bipym and (R 2SnCl 2) 2 bipym were synthesized and studied by 1H and 13C NMR spectroscopy in solution, and by IR and Mössbauer spectroscopy in the solid state and frozen solutions. The complexes Et 2SnCl 2 bipym · bipym and (Et 2SnCl 2) 2 bipym were characterized by X-ray diffraction methods. In both complexes the tin environment is octahedral with chloro atoms in a cis disposition, the ethyl groups in a trans disposition and two N atoms from the ligand bipym. the second complex is a centrosymmetric binuclear species that has the ligand lone-pairs bound to two Et 2SnCl 2 units, whereas the first has one Et 2SnCl 2 species bound to the ligand and one ligand uncoordinated. The data obtained by 119Sn Mössbauer spectroscopy for the solids and for frozen solutions indicate the presence of quadrivalent tin in an octahedral environment with trans alkyl groups, in keeping with the X-ray structures. The NMR spectra, however, reveal ligand lability in solution, and the CSnC angles calculated from coupling constants suggest a coordination number of between 5 and 6. These results together with the long SnN bond distances in crystals of Et 2SnCl 2bipym · bipym and (Et 2SnCl 2) 2 bipym suggest that these complexes may have a potential antitumour activity.