POLYNUCLEAR COMPLEXES OF RU(II) BASED ON THE OCTADENTATE LIGAND 5,5'-BIS(2-PYRIDYL)-3,3'-BI(1,2,4-TRIAZOLE) (BPBT) - SYNTHESIS, SPECTROSCOPIC AND PHOTOPHYSICAL PROPERTIES

The synthesis and characterization of the redox and excited state prop erties of three complexes (Ru(bpy)(2)(bpbtH(2))(2+), [Ru(bpy)(2)](2)(b pbtH(2))(4+) and [Ru(bpy)(2)](3)(bpbt)(4+)) derived from the title lig and ''bpbt'' are reported. The coordination of the Ru(bpy)2 unit is be lieved to occur via N-1 of the triazole and the pyridine nitrogen in t he mononuclear and binuclear complexes. In the trinuclear complex the third unit is linked via N-4 and N-4' of the bis(triazole) part of the ligand. Electrochemical studies of the mono-, bi- and trinuclear comp lexes show one, two and three one-electron oxidations(s) of the Ru-cen ter(s). On the reduction side, up to -2.0 V only reduction of the spec tator ligands bpy can be observed, each as two waves involving one, tw o and three electrons in the mono-, bi- and trinuclear complexes, resp ectively. FAB mass spectral data and fragmentation patterns of the bin uclear complex are discussed. Mixed-valence forms of the bi- and trinu clear complexes can be prepared by chemical oxidation and these show s trong absorption in the infra-red region corresponding to intervalence (IT) transitions. Analysis of the IT bands shows that the extent of e lectron delocalization is quite high in both cases, suggesting a fairl y strong metal-metal interaction. The lowest excited state in all case s involves charge transfer from Ru(II) to the bipyridine ligands, Ru(I I)-->bpy. All three complexes show emission in solution at ambient tem perature. The absorption and emission properties are sensitive to solu tion pH. Laser flash photolysis studies show a strong intensity depend ence for the luminescence and transient absorptions and this is attrib uted to excited state annihilation processes, possibly via electron tr ansfer.