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Lanthanide Triple Helical Complexes with a Chiral Bis(benzimidazole)pyridine Derivative
Author(s) -
Muller Gilles,
Riehl James P.,
Schenk Kurt J.,
Hopfgartner Gérard,
Piguet Claude,
Bünzli JeanClaude G.
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200212)2002:12<3101::aid-ejic3101>3.0.co;2-9
Subject(s) - chemistry , lanthanide , ligand (biochemistry) , pyridine , crystallography , diastereomer , luminescence , crystal structure , quantum yield , stereochemistry , medicinal chemistry , fluorescence , ion , organic chemistry , physics , quantum mechanics , biochemistry , receptor , optoelectronics
The ligand neopentyl 2,6‐bis[(1‐methylbenzimidazol‐2‐yl)]pyridine‐4‐carboxylate ( L 12 ) 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( L 12 ) 3 ] 3+ complexes. The crystal structure of ligand L 12 shows the expected trans ‐ trans conformation of the tridentate binding unit. The ligand forms stable 1:3 complexes in anhydrous acetonitrile (logβ 3 in the range 17.3−19.0, log K 3 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 L 12 appears to favour a 3 ππ*‐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 D 3 local symmetry at the metal ion site. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)