Stereochemistry and polymetallic ligand-bridged molecular assemblies

There have been many recent developments in synthetic methodologies for polymetallic ligand-bridged molecular assemblies, encouraged by the prospect that such materials have potential application to photochemical molecular devices. The assemblies have involved ruthenium (II) metal centers, which are invariably octahedral. However, the synthetic advances have often occurred without consideration of the problem of stereochemical ambiguity in the produets. The present review examines this uncertainty and ways in which it may be addressed. In particular, it assesses approaches to the pre-determination of the stereochemistry of poly-nuclear 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 chiomophore-quencher complexes and of dinuclear and trinuclear ligand-bridged species. Additionally, the review summarizes our preliminary studies of their physical properties as a function of the spatial arrangement of the components