Crystal and molecular structure of tetra-µ3-carbonyl-octacarbonyl-tetrakis(triphenyl phosphite)-octahedro-hexarhodium

Abstract

The title compound, [Rh₆(µ₃-CO)₄(CO)₈{P(OPh)₃}₄], crystallises in the orthorhombic space group Aba2 with cell dimensions a= 19.654(5), b= 21.474(7), c= 19.955(4)Å, and Z= 4. The structure determination is based on 3 478 independent X-ray counter data, refinement being carried out by blocked matrix leat squares to a conventional R value of 0.038. The molecule contains a slightly distorted octahedral cluster, with a mean Rh–Rh bond length of 2.789 Å. The ligand stereochemistry is derived from that of the parent [Rh₆(CO)₁₆] species, with four terminal CO groups substituted by triphenyl phosphite ligands, bound to four ‘equatorial’ coplanar rhodium atoms (mean Rh–P 2.265 Å). The Rh–C and C–O bond lengths for the terminal CO groups have mean values 1.88 and 1.14 Å respectively. The four triple-bridging carbonyls are slightly but significantly asymmetric, showing shorter bonds to the Rh atoms bearing the phosphite ligands (mean Rh–C 2.16 vs. 2.24 Å).