Synthesis, spectroscopic (Mossbauer, 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

The ligand 2,2'-bipyrimidine (bipym) was reacted with diorganotins R(2)SnCl(2) (R = methyl, ethyl) and complexes of the types R(2)SnCl(2)bipym, R(2)SnCl(2)bipym . bipym and (R(2)SnCl(2))(2)bipym were synthesized and studied by H-1 and C-13 NMR spectroscopy in solution, and by IR and Mossbauer spectroscopy in the solid state and frozen solutions. The complexes Et(2)SnCl(2)bipym . bipym and (Et(2)SnCl(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(2)SnCl(2) units, whereas the first has one Et(2)SnCl(2) species bound to the ligand and one ligand uncoordinated. The data obtained by Sn-119 Mossbauer 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(2)SnCl(2)bipym . bipym and (Et(2)SnCl(2))(2)bipym suggest that these complexes may have a potential antitumour activity.