Jean-Claude Bunzli - Structural, photophysical and chiro-optical properties of lanthanide complexes with a bis(benzimidazole)pyridine-based chiral ligand

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      Publication Details (including relevant citation   information):

      Muller,G., Maupin,C.L., Riehl,J.P., Birkedal,H., Piguet,C.,   Bunzli,J.C.G. European Journal of Inorganic Chemistry  2003 (22) 4065-4072

      Abstract: The neutral Ln(III) 1:1 nitrato   complexes with the chiral ligand   2,6-bis(1-S-neopentylbenzimidazol-2-yl)pyridine (L-11) have been   synthesised and their stability constants measured in   acetonitrile (log K-1 = 4.0-6.4). The crystal and molecular   structure of [Eu(NO3)(3)(L-11)(MeCN)] shows the typical   meridional planar coordination of L-11 to the metal ion and low   symmetry of the coordination polyhedron. The influence of the   steric hindrance generated by the substituent at R-2 on the   crystal packing and bond lengths is discussed. Photophysical   measurements show that ligand L-11 induces a (3)pipi*-to-Ln   energy-transfer process in the Eu-III complex, while the Tb-III   compound is ten times less luminescent. Addition of a second   molecule of L-11 to give [Ln(ClO4)(2)(L-11)(2)](+) leads to a   large quenching of the Eu-III luminescence (140-fold) due to   several factors: a less efficient (1)pipi*-->(3)pipi* transfer   (ca. fourfold), a smaller intrinsic quantum yield Q(Eu) (ca.   threefold), and a substantially less efficient ligand-to-metal   transfer (ca. 12-fold). In the case of the Tb-III complex, the   decrease in the energy of the triplet state reduces further the   Tb-III emission through increased back transfer. The specific   rotary dispersion of the 1:1 and 1:2 complexes points to the   chirality of the complexes arising mainly from the ligand, while   the circularly polarized luminescence of these complexes with   Eu-III and Tb-III displays a weak effect, pointing to a small   diastereomeric excess in solution. Altogether, this study   demonstrates that electronic, thermodynamic and photophysical   properties of lanthanide complexes with aromatic terdentate   ligands can be tuned by modifying the number and the arrangement   of the ligands, as well as their substituents, particularly those   in the R-2 and R-3 positions

      Address (URL): J INORG CHEM