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 µ-l 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.