Synthesis, nuclear magnetic resonance and crystallographic studies of six-co-ordinate bis(bidentate ligand)-dihalogenotin(IV) complexes

Six co-ordinate tin(IV) complexes of the type SnL2X2 have been prepared (where HL is a monobasic chelating ligand and X = Cl, Br or I). They have been characterised by elemental analysis, H-1 and Sn-119 NMR, positive-ion fast atom bombardment and electron-impact mass and vibrational spectroscopy. Three distinct Sn-119 NMR chemical shift ranges are observed depending on the halogen, demonstrating the relationship between the shielding of the tin nucleus and the electronegativity of the halogens. Geometrical isomerism was normally slow on the NMR time-scale and in some cases slow- and fast-exchange spectra were obtained by variable-temperature Sn-119 NMR spectroscopy. The crystal structures of two examples are reported. Both have non-crystallographic C2 symmetry with the halides cis. The structures represent different configurational isomers further illustrating the facile interconversion between isomers in solution.