Imidazolate bridged polynuclear rhodium(I) complexes. X-ray structure of [Rh(2-Meimidazolate)(CO)2]4

The synthesis and properties of polynuclear complexes of general formulae M(RIm)(diolefin)_x, M(RIm)(CO)₂]_x and M(RIm)(CO)L]_x (M  Rh, Ir; RIm  imidazolate, 2-methylimidazolate, 2-benzylbenzimidazolate; L  PPh₃ or P(OPh)₃) are reported. The crystal structure of the novel complex Rh(2-MeIm)-(CO)₂]₄ (2-MeIm  2-methylimidazolate) has been determined by X-ray methods. The crystals are orthorhombic, space group P2₁2₁2₁, with Z  4 in a unit cell of dimensions a 19.427(12), b 13.419(8), c 12.346(9) Å. The structure has been solved by combined Patterson and direct methods and refined by full-matrix least-squares to R  0.043 for 937 independent observed reflections. It consists of discrete tetrameric complexes in which each Rh atom is in a nearly cis square planar arrangement, bonded to two carbon atoms of carbonyl groups and to two nitrogen atoms of two 2-methylimidazolate ligands, each of which, acting as an exo-bidentate ligand, bridging two metal atoms, so that the four bridging 2-MeIm ligands and the four Rh atoms form a multiatomic ring.