Ruthenium Osmium Assembly

Although the above discussion is centered on the synthesis of polymeric osmium and ruthenium complexes, the methods employed are also very successful in the preparation of mononuclear complexes. In this context, the preparation of ruthenium or osmium complexes which are suitable for the formation of self-assembled monolayers (see Section 4.3 above) can be prepared by using the same approach. Starting from the precursor [M(bpy)2Cl2], one chloride atom can be replaced to yield complexes of the type [M(bpy)2Cl L]+, where L is the surface active ligand. In the presence of water, species of the type [M(bpy)2(L)2]2+ are obtained. 

P-Cyclodextrines, appended to a ruthenium complex, have been employed as hosts for iridium and osmium complexes bearing adamantyl or biphenyl moieties, which form strong host-guest complexes with P-cyclodextrines (see Fig. 3). In such systems, photoinduced energy transfer can occur from the periphery, upon complexation of the iridium units, toward the central ruthenium acceptor, or switched in the other direction, from the ruthenium to the periphery when the osmium moieties are assembled (see Fig. 3) 42). The lowest excited state is in fact localized on the osmium center, while the highest luminescent excited state belongs to the iridium complex (see Fig. 3 right). 

Fig. 3. Schematic representation of the assembled Ru—CD—Ir system in which it is possible, upon light excitation, to funnel the electronic excitation to the ruthenium core. To switch the direction of the energy transfer process, Ir complexes must be replaced with the osmium analogues. Right emission spectra for the three complexes.

Armaroli. N. Barigelletti. F. Calogero, G. Flamigni, L. White, C.M. Ward, M.D. Electronic energy transfer between ruthenium(II) and osmium(II) polypyridyl lumino-phores in a hydrogen-bonded supramolecular assembly. Chem. Commun. 1997, (22), 2181-2182. 

Encinas. S. Simpson, N.R.M. Andrews, P. Ward. M.D. White, C.M. Armaroli, N. Barigelletti, F. Houlton. A. Photoinduced energy transfer within hydrogen-bonded multi-component assemblies based on a ruthenium-poly-pyridyl donor and an osmium-polypyridyl or ferrocenyl acceptor. New J. Chem. 2000, 24 (12). 987-991. 

Constable, E.C. and Cargill Thompson, A.M.W. (1992) Ligand reactivity in iron(II) complexes of 4 -(4 "-pyridyl)-2,2 6, 2"-terpyridine J. Chem. Soc., Dalton Trans., 2947-2950 Constable, E.C. and Cargill Thompson, A.M.W. (1994) Pendant-functionalised ligands for metallosupramolecular assemblies ruthenium(II) and osmium(II) complexes of 4 -(4-pyridyl)-2,2 6, 2"-terpyridine J. Chem. Soc., Dalton Trans., In the press... 

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