STRUCTURAL SYSTEMATICS IN PENTANUCLEAR AND HEXANUCLEAR METAL-CLUSTERSCONTAINING CARBOCYCLIC LIGANDS

This article describes the structural chemistry of penta- and hexanucl ear ruthenium and osmium carbonyl clusters which contain one or more a rene (eta(6)-Ar) Or cyclopentadienyl (eta(5)-Cp) groups, and compares and contrasts their structures with those of related binary carbonyl a nd carbonyl hydride clusters. The pentanuclear structures described ar e based on the trigonal bipyramidal metal framework, or on frameworks derived from this by the cleavage of one or more metal-metal edges. Th e steric and electronic factors which determine the position of the M( eta(6)-Ar) or M(eta(5)-Cp) units in the framework are discussed. For t he hexanuclear clusters two basic metal core geometries are observed, the bicapped tetrahedron, comprising three fused tetrahedra, and the o ctahedron. The two series of compounds exhibit guile different structu ral chemistries. The bicapped tetrahedral structures exhibit quite ext ensive isomerism for the carbocyclic ligand substituted complexes, the positions of the M(eta(6)-Ar) or M(eta(5)-Cp) being dependent on both steric and electronic factors. For the octahedral carbocyclic ligand substituted complexes isomerism is less prevalent, but an analysis of the ligand polyhedra in these systems shows that low energy transforma tions, consistent with the fluxional properties of these complexes, ar e possible. The metal core geometries and ligand polyhedral geometries of related series of hexanuclear clusters are analysed statistically using half-normal probability plots and scatter plots. (C) 1998 Elsevi er Science Ltd. All rights reserved.