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Ruthenium(II) as a Novel "Labile" Partner in Thermodynamic Self-Assembly of Heterobimetallic d-f Triple-Stranded Helicates

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Published in Chemistry - A European Journal. 2004, vol. 10, no. 14, p. 3503-3516
Abstract Unsymmetrical substituted bidentate benzimidazol-2-ylpyridine ligands L2 and L3 react with [Ru(dmso)4Cl2] in ethanol to give statistical 1:3 mixtures of fac-[Ru(Li)3]2+ and mer-[Ru(Li)3]2+ (i=2, 3; Gisomerisation=-2.7 kJ mol-1). In more polar solvents (acetonitrile, methanol), the free energy of the facialmeridional isomerisation process favours mer-[Ru(Li)3]2+, which is the only isomer observed in solution at the equilibrium (Gisomerisation-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 (RuC60H51N9O8Cl2, monoclinic, P21/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 facialmeridional isomerisation is reversed (Gisomerisation11.4 kJ mol-1), and the RuN bonds are labile enough to allow the quantitative thermodynamic self-assembly of HHH-[RuLu(L1)3]5+ within hours ([RuLu(L1)3](CF3SO3)4.5Cl0.5(CH3OH)2.5: RuLuC106H109Cl0.5N21O19S4.5F13.5, triclinic, P, Z=2). Electrochemical and photophysical studies show that the benzimidazol-2-ylpyridine units in L1-L3 display similar -acceptor properties to, but stronger -donor properties than, those found in 2,2-bipyridine. This shifts the intraligand * 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+.
Keywords Helical structuresIsomerizationLanthanidesRutheniumSelf-assembly
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Research group Groupe Hauser
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TORELLI, Stéphane et al. Ruthenium(II) as a Novel "Labile" Partner in Thermodynamic Self-Assembly of Heterobimetallic d-f Triple-Stranded Helicates. In: Chemistry - A European Journal, 2004, vol. 10, n° 14, p. 3503-3516. https://archive-ouverte.unige.ch/unige:3258

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Deposited on : 2009-09-21

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