Five-Coordinate Nickel(III). The Crystal and Molecular Structure of NiBr8(P(C8H5)(CH3)(2))(2).0.5NiBr(2)(P(C6H5)(CH3)O-2.C6H6

The crystal and molecular structure of the 1:0.5:1 adduct of tribromobis(phenyldimethylphosphine)nickel(III), dibromobis(phenyldimethylphosphine)nickel(II), and benzene has been determined from three-dimensional X-ray data collected by counter methods. The structure has been refined by least-squares techniques to a final R factor on F of 0.054. The material crystallizes in space group (C1P)-P-1 (1) over bar of the triclinic system, with two molecules of NiBr5(P(C6H5)(CH3)02, one molecule of NiBrs(P(C6H5)(CH3)2}2, and two molecules of benzene in a cell of dimensions a = 9.021 (5), b = 17.951 (10), c = 11.181 (6) A; a = 98 52 (1)', = 940 29 (1)', = 90 44 (1)'. The observed and calculated densities are 1.67 +/- 0.02 and 1.68 g/cma, respectively. The four- and five-coordinate molecules are well separated. The trans-planar complex NiBr3(P(C6H6)(Clis)(2))(2) is crystallographically required to possess a center of inversion; the Ni-P and Ni-Br bond lengths are 2.251 (3) and 2.297 (2) angstrom, respectively. The five-coordinate Ni(III) complex NiBra(P(C6H6)(CH3)2)2 possesses a trigonal-bipyramidal geometry with axial phosphine groups. There is a slight distortion of the molecule in the plane of the Ni and three Br atoms, which could arise from Jahn-Teller effects. The Ni-P bond distances arc 2.263 (3) and 2.273 (3) A, and the Ni-Br bond distances are 2.349 (2), 2.375 (2), and 2.339 (2) angstrom.