Cation-exchange chromatographic techniques have been developed to separate stereoisomers of polymetallic complexes, using SP Sephadex C-25 as support. Through the example of the ligand-bridged dinuclear cation [{Ru(dmbpy) 2 } 2 (µ-bipym)] 4ϩ (dmbpy = 4,4Ј-dimethyl-2,2Ј-bipyridine, bipym = 2,2Ј-bipyrimidine), the isolation and characterisation of the meso and rac diastereoisomers by elution with aqueous sodium toluene-4-sulfonate solution are demonstrated. The effects of variation in salt concentration and temperature on the efficacy of the separation are discussed. The enantiomeric pair of the rac diastereoisomer (∆∆ and ΛΛ) was subsequently chromatographically resolved on SP Sephadex C-25, relying upon the inherent chirality of the support. Optical resolutions using eluents with chiral anions [aqueous sodium (ϩ)-O,OЈ-dibenzoyl--tartrate and sodium (Ϫ)-O,OЈ-dibenzoyl--tartrate] were investigated, with the (Ϫ)-enantiomer demonstrating a positive [the (ϩ)-enantiomer a negative] synergistic effect in combination with the Sephadex support. Crystals of the meso form were isolated, allowing an X-ray structural determination.The study of polymetallic 'supramolecular' assemblies is a rapidly expanding field of chemistry, largely because of their potential application in materials for such diverse purposes as photochemical molecular devices, 1-4 and as photoprobes of structure and function of polynucleotides such as DNA. 5-9 In particular, much attention has been focused upon the polypyridyl complexes of ruthenium and osmium as the basis for such assemblies as a result of their favourable photochemical and redox characteristics. 1 When bidentate ligands are involved in such centres, stereoisomerism is inherent in the resultant assemblies, but surprisingly this problem has until recently received only tacit attention.In general, studies of chirality in octahedral tris(bidentate ligand)ruthenium() centres have been limited to mononuclear species, and isolation of enantiomers has relied on the sometimes inefficient technique of diastereoisomer formation using chiral auxiliary anions. 10-13 Such complexes can then be used as chiral building blocks for larger assemblies, 12 but this approach requires tedious synthetic procedures where care must be taken to preserve the chiral integrity at each metal centre during every reaction step. Additionally, in the vast majority of the targets studied, crystallisation has proved the most favourable method of diastereoisomeric discrimination. Our aim was to develop general chromatographic techniques for the separation of stereoisomers not only of mononuclear complexes, but also of oligomeric transition-metal assemblies containing polypyridyl ligands. In the latter case the simplest example is that of a dinuclear complex of the type [{Ru(pp) 2 } 2 (µ-L b )] nϩ [pp is a symmetrical bidentate ligand, L b is a bis(bidentate) bridging ligand]. There are the possibilities of the meso (Λ∆) and the rac diastereoisomers, the rac form consisting of an enantiomeric pair (ΛΛ and ∆∆), as illustrat...

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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The potential of IR absorption and Raman spectroscopy for rapid identification of novel psychoactive substances (NPS) has been tested using a set of 221 unsorted seized samples suspected of containing NPS. Both IR and Raman spectra showed large variation between the different sub-classifications of NPS and smaller, but still distinguishable, differences between closely related compounds within the same class. In initial tests, screening the samples using spectral searching against a limited reference library allowed only 41% of the samples to be fully identified. The limiting factor in the identification was the large number of active compounds in the seized samples for which no reference vibrational data were available in the libraries rather than poor spectral quality. Therefore, when 33 of these compounds were independently identified by NMR and mass spectrometry and their spectra used to extend the libraries, the percentage of samples identified by IR and Raman screening alone increased to 76%, with only 7% of samples having no identifiable constituents. This study, which is the largest of its type ever carried out, therefore demonstrates that this approach of detecting non-matching samples and then identifying them using standard analytical methods has considerable potential in NPS screening since it allows rapid identification of the constituents of the majority of street quality samples. Only one complete feedback cycle was carried out in this study but there is clearly the potential to carry out continuous identification/updating when this system is used in operational settings.