NEUTRAL PHOSPHINE COMPLEXES OF ANTIMONY(III) AND BISMUTH(III) HALIDES

The reaction between BiBr3 and PEt3 has afforded crystals of the centrosymmetric, tetrameric complex [Bi4Br12(PEt3)4] in which each bismuth centre is octahedrally co-ordinated and bonded to one phosphine ligand. An alternative structural arrangement for a monophosphine complex has been found in a PMe3 complex of SbI3, [{SbI3(PMe3)}x], which is polymeric although with mu-1 bridges of two types between the antimony centres such that a description as a polymer of dimers is appropriate. In the bis(phosphine) complex of BiBr3, [Bi2Br6(PMe3)4], a centrosymmetric, edge-shared, bioctahedral structure is observed with cis phosphines occupying one axial and one equatorial site per bismuth centre. Similar structures have been observed for the dmpe complexes [E2Br6(dmpe)2] [E = Sb or Bi; dmpe = 1,2-bis(dimethylphosphino)ethane] and the factors affecting which structural isomer is adopted, in comparison with a range of transition metal complexes, have been discussed. An isomeric tetrameric form of [SbBr3(dmpe)] has also been isolated.