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Lanthanide triple helical complexes with a chiral bis(benzimidazole)pyridine derivative

Muller, Gilles
Riehl, James P.
Schenk, Kurt J.
Bünzli, Jean-Claude G.
Published in European Journal of Inorganic Chemistry. 2002, vol. 2002, no. 12, p. 3101-3110
Abstract The ligand neopentyl 2,6-bis[(1-methylbenzimidazol-2-yl)]pyridine-4-carboxylate (L12) has been synthesised to test the effect of the chiral neopentyl ester group in the 4-position of the pyridine ring on (i) the helical wrapping, (ii) the diastereomeric induction and (iii) the thermodynamic and photophysical properties of the [Ln(L12)3]3+ complexes. The crystal structure of ligand L12 shows the expected trans-trans conformation of the tridentate binding unit. The ligand forms stable 1:3 complexes in anhydrous acetonitrile (log3 in the range 17.3-19.0, logK3 in the range 2.9-4.6). The triple helical structure in solution is responsible for the four times larger specific rotary dispersion measured in the complexes. Circularly polarised luminescence of the Eu triple helical complex displays a weak effect, suggesting a small diastereomeric excess in solution. Ligand L12 appears to favour a 3*-to-Ln energy transfer process for Eu, but temperature-dependent nonradiative processes lead to a very small quantum yield. High-resolution luminescence spectra indicate that the Eu complex has a distorted D3 local symmetry at the metal ion site.
Keywords LanthanidesTridentate ligandsChiralityLuminescenceStability constants
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MULLER, Gilles et al. Lanthanide triple helical complexes with a chiral bis(benzimidazole)pyridine derivative. In: European Journal of Inorganic Chemistry, 2002, vol. 2002, n° 12, p. 3101-3110. doi: 10.1002/1099-0682(200212)2002:12<3101::AID-EJIC3101>3.0.CO;2-9 https://archive-ouverte.unige.ch/unige:2360

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Deposited on : 2009-08-10

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