Monomeric ruthenium() complexes [Ru(L) 3 ] 2ϩ containing unsymmetric bipyridine ligands [Where L = 5-methyl-2,2Ј-bipyridine (L 1 ), 5-ethyl-2,2Ј-bipyridine (L 2 ), 5-propyl-2,2Ј-bipyridine (L 3 ), 5-(2-methylpropyl)-2,2Ј-bipyridine (L 4 ), 5-(2,2-dimethylpropyl)-2,2Ј-bipyridine (L 5 ) or 5-(carbomethoxy)-2,2Ј-bipyridine (L 6 )] have been studied and the meridional and facial isomers isolated by the use of cation-exchange column chromatography (SP Sephadex C-25) eluting with either sodium toluene-4-sulfonate or sodium hexanoate. The relative yield of the facial isomer was found to decrease with increasing steric bulk, preventing the isolation of fac-[Ru(L 5 ) 3 ] 2ϩ . The two isomeric forms were characterized by 1 H NMR spectroscopy, with the complexes [Ru(L 1-3 ) 3 ] 2ϩ demonstrating an unusually large coupling between the H 6 and H 4 protons. Crystals suitable for X-ray structural analysis of [Ru(L 1 ) 3 ] 2ϩ were obtained as a mixture of the meridional and facial isomers, indicating that separation of this isomeric mixture could not be achieved by fractional crystallisation. The optical isomers of the complex [Ru(L 3 ) 3 ] 2ϩ were chromatographically separated on SP Sephadex C-25 relying upon the inherent chirality of the support. It is apparent that chiral interactions can inhibit geometric isomer separation using this technique.
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