SYNTHESES AND STRUCTURES OF DIMESITYLBISMUTH(III) BROMIDE, MES2BIBR, AND BIS(DIPHENYLDITHIOPHOSPHINATO)MESITYLBISMUTH(III), MESBI(S2PPH2)2

Addition of BiBr3 to Mes3Bi (Mes = 2, 4, 6-Me3C6H2) in Et2O gives 86% of MeS2BiBr (1) as yellow crystals. Reaction of 1 with Ph2PS2NH4 in a 1:1 molar ratio gives a quantitative yield of MesBi(S2PPh2)2 (2) rather than the expected dimesitylbismuth compound. The crystal and molecular structures of 1 and 2 were determined at 153 K and 173 K, respectively. They contain Mes2BiBr molecules with trigonal pyramidal coordination around Bi. The mean Bi-C bond distance is 2.27 angstrom and the Bi-Br bond distance is 2.690(2) angstrom. The angles around Bi vary between 89.4 and 106.4-degrees. Intermolecular Bi...Br contacts of 3.795 angstrom, indicating weak secondary bonding, give rise to zig-zag shaped (Bi-Br)x chains. In the polymeric chain the coordination geometry around bismuth atoms can be described as pseudo-trigonal bipyramidal. The crystals of 2 consist of discrete monomeric MesBi(S2PPh2)2 molecules with a symmetry plane containing the metal atom and the aromatic ring of the attached mesityl group. The dithiophosphinato ligands exhibit an anisobidentate coordination pattern with long and short phosphorus-sulfur bonds, i.e. P(1)-S(1) 2.051(31) angstrom and P(1)-S(2) 1.980(3) angstrom, related to short and long bismuth-sulfur distances, respectively, i.e. Bi-S(1) 2.662(2) angstrom and Bi-S(2) 3.123(3) angstrom. This leads to a square-pyramidal geometry around the bismuth atom, with the metal lying 0.33 angstrom above the basal plane formed by the four sulfur atoms.