Structural studies on aryl bismuth halides and halogenoanions. Part 4. Neutral Lewis base adducts of aryl bismuth dibromide and diaryl bismuth bromide compounds

Abstract

Structural studies by X-ray crystallography have been carried out for a range of Lewis base ligand complexes of arylbismuth dibromides and diarylbismuth bromides. The complexes [Bi 2Ph 2Br 4(OPPh 3) 2] 17 and [Bi 2Ph 2Br 4(dmpu) 2] 18 (dmpu = N, N′-dimethylpropylene urea) both adopt crystallographically centrosymmetric bromine-bridged dimeric structures, each bismuth centre having a five-coordinate, square-based pyramidal geometry. In both structures a phenyl group occupies the apical site whilst the four basal positions are occupied by three bromine atoms, one terminal and two bridging, and the oxygen atom of the coordinated ligand (OPPh 3 in 17 and dmpu in 18). A bis ligand complex [BiPhBr 2(dmpu) 2] 19 is monomeric, with a similar coordination geometry around the bismuth centre in which the four basal positions are occupied by two cis bromine atoms and two cis oxygen atoms from the coordinated dmpu ligands. The diarylbismuth halide complexes [Bi(mes) 2Br(OSPh 2)] 20 (mes = 2,4,6-Me 3C 6H 2) and [Bi(mes) 2Br(hmpa)] 21 (hmpa = hexamethylphosphoramide, OP(NMe 2) 3) are both monomeric, each bismuth centre having a four-coordinate, disphenoidal geometry with axial bromine and ligand donor atoms and equatorial mesityl groups. The structures are compared with those of related compounds and some general structural principles are derived and bonding models advanced.