STEREOCHEMISTRY AND POLYMETALLIC LIGAND-BRIDGED MOLECULAR ASSEMBLIES

There have been many recent developments in synthetic methodologies fo r polymetallic ligand-bridged molecular assemblies, encouraged by the prospect that such materials have potential application to photochemic al molecular devices. The assemblies have involved ruthenium(II) metal centers, which are invariably octahedral. However, the synthetic adva nces have often occurred without consideration of the problem of stere ochemical ambiguity in the products. The present review examines this uncertainty and ways in which it may be addressed. In particular, it a ssesses approaches to the pre-determination of the stereochemistry of polynuclear assemblies incorporating Ru(II) and related centers {e.g. Os(II)} by the use of precursors with an established geometry, and the use of chromatographic techniques in the separation of stereoisomeric mixtures. Some of our own work is elaborated. where we have been able to separate stereoisomers of chromophore-quencher complexes and of di nuclear and trinuclear ligand-bridged species. Additionally, the revie w summarizes our preliminary studies of their physical properties as a function of the spatial arrangement of the components. (C) 1997 Elsev ier Science S.A.