760949-34-6Relevant articles and documents
Ruthenium(II) as a novel labile partner in thermodynamic self-assembly of heterobimetallic d-f triple-stranded helicates
Torelli, Stephane,Delahaye, Sandra,Hauser, Andreas,Bernardinelli, Gerald,Piguet, Claude
, p. 3503 - 3516 (2004)
Unsymmetrical substituted bidentate benzimidazol-2-ylpyridine ligands L2 and L3 react with [Ru(dm-so)4Cl2] in ethanol to give statistical 1:3 mixtures of fac-[Ru(Li)3]2+ mer-[Ru(Li)3]2+ (i=2, 3; ΔGθ isomerisation= -2.7 kJ mol-1). In more polar solvents (acetonitrile, methanol), the free energy of the facial?meridional isomerisation process favours mer-[Ru(Li)3]2+, which is the only isomer observed in solution at the equilibrium (ΔGθ isomerisation≤-11.4 kJ mol-1). Since the latter process takes several days for [Ru(L2)3]2+, fac-[Ru(L2) 3]2+ and mer-[Ru(L2)3]2+ have been separated by chromatography, but the 28-fold increase in velocity observed for [Ru (L3)3]2+ provides only mer-[Ru(L3)3] (ClO4)2 after chromatography (RuC60H 51N9O8Cl2, monoclinic, P2 1/n, Z=4). The facial isomer can be stabilised when an appended tridentate binding unit, connected at the 5-position of the benzimidazol-2- ylpyridine unit in ligand L1, interacts with nine-coordinate lanthanides (III). The free energy of the facial?meridional isomerisation is reversed (ΔGθisomerisation≥ 11.4 kJ mol-1), and the Ru-N bonds are labile enough to allow the quantitative thermodynamic self-assembly of HHH-[RuLu(L1)3]5+ within hours ([RuLu(L1)3](CF3SO3)4.5Cl 0.5(CH3OH)2.5: RuLuC106H 109Cl0.5N21O19S4.5F 13.5, triclinic, P1, Z=2). Electrochemical and photophysical studies show that the benzimidazol-2-ylpyridine units in L1-L3 display similar π-acceptor properties to, but stronger π-donor properties than, those found in 2,2′-bipyridine. This shifts the intraligand π→π * and the MLCT transitions toward lower energies in the pseudo-octahedral [Ru(Li)3]2+ (i=2, 3) chromophores. The concomitant short lifetime of the 3MLCT excited state points to efficient, thermally activated quenching via low-energy Ru-centred d-d states, a limitation which is partially overcome by mechanical coupling in HHH-[RuLu(L1)3] 5+.
