Synthesis, multinuclear magnetic resonance spectroscopic studies and crystal structures of mono- and di-selenoether complexes of tin(IV) halides

Reaction of SnX4 O(X=Cl or Br) with Me2Se or diselenoether ligands in dry CHCl3 produced white or yellow solids [SnX4L2] in high yield [X = Cl, L-2=MeSe(CH2)(n)SeMe, PhSe(CH2)(n)SePh (n = 2 or 3), C6H4(SeMe)(2)-o or 2Me(2)Se; X = Br, L-2 = MeSe(CH2)(n)SeMe (n = 2 or 3), C6H4(SeMe)(2)-o or 2Me(2)Se]. These compounds have been characterised by a combination of variable-temperature H-1, Sn-119-{H-1} and Se-77-{H-1} NMR, IR spectroscopy and microanalyses. Single-crystal X-ray diffraction studies on trans-[SnX4(SeMe2)(2)], [SnX4{C6H4(SeMe)(2)-o}] (X = Cl or Br) and [SnCl4(MeSe(CH2)(3)SeMe}] confirm distorted octahedral geometry at Sn-IV in each case, with the bidentate ligands chelating. The C6H4(SeMe)(2)-o complexes adopt the meso arrangement, while the ligand is in the DL form in [SnCl4{MeSe(CH2)(3)SeMe}]. The trends in d(Sn-X) and d(Sn-Se) reveal that the trans influence of halide is greater than that of selenium in these systems. In comparable systems d(Sn-Se) is longer in the bromo than in the chloro systems, consistent with the greater Lewis acidity of SnCl4. The NMR studies revealed that pyramidal-inversion and ligand;dissociation processes are facile. In the SeMe, complexes both cis and trans isomers are present, while in the diselenoether systems the meso and DL forms are both apparent at low temperatures. The co-ordination shifts in the Se-77-{H-1) NMR spectra are markedly dependent upon chelate-ring size; the first time this has been observed for complexes of a p-block metal.