SYNTHESIS AND CRYSTAL-STRUCTURE OF TRIBROMOMETHYLTRIPHENYLPHOSPHONIUM BROMIDE AND BIS(TRIBROMOMETHYLTRIPHENYLPHOSPHONIUM) TRIBROMIDE BROMIDE

Tribromotriphenylphosphonium bromide I has been prepared by the reaction of triphenylphosphine with tetrabromomethane in dichloromethane. Colourless crystals were obtained by recrystallization from the same solvent. The light-sensitive crystals change colour to yellow. The crystals are triclinic, space group P (1) over bar, Z = 4, a = 1008.6(5), b = 1357.8(6), c = 1560.7(7) pm, alpha = 106.61(4), beta = 91.80(4), gamma = 93.88(4)degrees. In the solid state there are discrete monomeric (C6H5)(3)PCBr3+ cations and Br- anions. The cation has a slightly irregular tetrahedral geometry around the P atom. The crystals contain one molecule CH2Cl2 per four molecules (C6H5)(3)PCBr4. Bis(tribromomethyltriphenylphosphonium) tribromide bromide 2 can be obtained as a byproduct of the reaction of (C6H5)(3)P with CBr4 by variation of the reaction conditions. Red light-stable crystals are obtained by recrystallization from CH2Cl2. The crystals are monoclinic, space group C2/c, Z = 8, a = 2231.5(7), b = 1532.7(7), c = 1556.9(6) pm, beta = 129.69(2)degrees. In the solid state bis(tribromomethyltriphenylphosphonium) tribromide bromide exists as discrete monomeric (C6H5)(3)PCBr3+ cations and Br- and Br-3(-) anions. The Br anion and the central Br of Br-3(-) anion lie on crystallographic twofold axes. The cation has also a slightly irregular tetrahedral geometry around the P atom, with a long P-CBr3 bond.