Allogons: isomerism in the crystal and molecular structure of the green form of dibromobis(benzyldiphenylphosphine)nickel(II); Ni[P(CH2Ph)Ph2]2Br2[square], 2Ni[P(CH2Ph)Ph2]2Br2[tetrahedral]

Abstract

The crystal structure of the green paramagnetic form of dibromobis(benzyldiphenylphosphine)nickel(II), determined from 3500 photographically observed intensities and refined to an R of 9·9%, shows that the triclinic unit cell contains three single molecules. One molecule has its nickel atom on a centre of symmetry and has the trans square-planar configuration. The other two molecules are related to each other by a centre of symmetry; their nickel bonds are arranged tetrahedrally. The whole is a molecular compound, Ni[P(CH₂Ph)Ph₂]₂Br₂[square], 2Ni[P(CH₂Ph)Ph₂]₂Br₂[tetrahedral], which is described as an interallogon compound. There is a significant difference between corresponding bond lengths in the two different stereochemical units, and this difference is the same for the two types of metal–ligand bond present; Ni–P (square-planar) 2·26, Ni–P (tetrahedral) 2·31, Ni–Br (square-planar) 2·30, and Ni–Br (tetrahedral) 2·35 Å.