Hepta- and higher nuclearity clusters

Changing two monophosphine for a diphosphine ligand converts the bicapped trigonal bipyramid, [HRu4Au3(CO)i2(PPh3)3] (43), to a bicapped-square pyramid, [HRu4Au3(CO)i2(PPh3)(dppm)] (44).[  

From all these results we can conclude that in most cases skeletal isomers are obtained under the same reaction conditions. When an equilibrium mixture is possible, one or other isomer can be obtained in the solid state by choosing the appropriate counter-anion, solvent, or rate of crystallization. A small change in a ligand, usually a phosphine, can also induce the precipitation of one isomer rather than the other. 

The different bonding mode of ligands to a metal core, usually accompanied by a change in the electron contribution to the cluster electron count, seems to be one of the major causes of skeletal isomerism. These ligands are mainly organic, sulfur-donor, or carbonyl ligands. Some other causes of skeletal isomerism are the bonding versatility of AuPRs, the unsaturation of 16e Pt centers, or the mere presence of an heterometal. 

The increasing number of metal clusters containing heterometal atoms and/or organic fragments suggest that skeletal isomerism will develop considerably in the near future. 

Catalysis and Dynamics and Physical Properties of Metal Clusters Edited by P. Braunstein, L. A. Oro P. R. Raithby Copyright WILEY-VCH Verlag GmbH, D-69469 Weinheim (Federal Republic of Germany), 1999 

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