Metal cluster topology. 19. Fused octahedra and trigonal bipyramids in iridium carbonyl clusters

In metal carbonyl clusters having fused polyhedral structures the octahedral cavities generally exhibit globally delocalized skeletal bonding topologies whereas the tetrahedral cavities exhibit edge-localized skeletal bonding topologies. Thus, the clusters Ir9(CO)203− and Ir12(CO)262− have structures based on the linear face-sharing fusion of two or three octahedra with numbers of skeletal electrons and orbitals consistent with multicenter delocalized core bonds in the centers of all of the octahedral cavities as well as surface bonding similar to the known simple octahedral Ir6(CO)16. More complicated partially delocalized skeletal bonding models can be analogously developed for the clusters Ir10(CO)212−, Ir11(CO)233−, and Ir12(CO)242− having various combinations of octahedral and tetrahedral cavities, with the latter cavities often appearing pairwise as trigonal bipyramids. The paramagnetic cluster Ir14(CO)27− has a 14-vertex ν2-trigonal bipyramid structure in which all 36 edges are parts of tetrahedral cavities consistent with an edge-localized skeletal bonding topology.