TRANSITION-METAL SCHIFF-BASE COMPLEXES AS LIGANDS IN TIN CHEMISTRY .5. STRUCTURAL STUDIES OF INTIMATE ION-PAIRED HETEROBIMETALLIC COMPLEXES OF TIN(IV) AND NICKEL, COPPER OR ZINC WITH 3-METHOXYSALICYLALDIMINE LIGANDS

1:1 Adducts have been formed between SnMe2(NCS)2 and SnBun2(NCS)2 with [Ni(3MeO-salpd)].H2O [3MeO-H2salpd = N,N-bis(3-methoxysalicylidene)propane-1,3-diamine] and [Ni(3MeO-salbn)].H2O [3MeO-H2salbn = N,N-bis(3-methoxysalicylidene)butane-1,4-diamine] and are best represented as the intimate ion-paired adducts [SnR2]2+.[NiL(NCS)2]2- [L = Schiff-base ligand; R = Me or Bu(n)] in each of which the tin atom sits in the plane of, and is held by donor bonds from, the four Schiff-base oxygen atoms. A crystal-structure determination of [SnMe2]2+.[Ni(3MeO-salpd)(NCS)2]2- revealed a tin co-ordination geometry which can be described as skew trapezoidal bipyramidal. The large unoccupied volume of thetin co-ordination sphere results in tin readily increasing its co-ordination number to seven, as demonstrated crystallographically in [SnMe2.dmf]2+.[Ni(3MeO-salpd)(NCS)2]2+ (dmf = dimethylformamide), which contains tin in a pentagonal-bipyramidal co-ordination environment with trans methyl groups and five donor oxygen atoms in the equatorial plane. X-Ray structural studies of both [SnBun2]2+. [Ni(3MeO-salpd) (NCS)2] 2- and [SnBun2]2+.[Ni(3MeO-salbn)(NCS)2]2- revealed the presence of molecular association resulting from weak intermolecular thiocyanate contacts, thus providing each tin with pseudo-pentagonal-bipyramidal co-ordination geometry. These latter adducts readily formed tin donor bonds with dmf. The 1:1 adduct formed between SnPh2(NCS)2 and [Ni(3MeO-salpd)].H2O was shown, from an X-ray crystallographic study, to be the intimate ion-paired heterobimetallic complex [SnPh2(NCS)]+.[Ni(3MeO-salpd)(NCS)(MeCN)]- in which tin has pentagonal-bipyramidal geometry with trans phenyl groups. Infrared and tin-119 Mossbauer spectroscopic data clearly demonstrate that a similar pentagonal-bipyramidal co-ordination geometry exists about tin in the complexes [SnR2(NCS)]+.[ML(NCS)]-.nH2O (R = Me or Bu(n); M = Cu or Zn; n = 0, 1 or 2).