Jean-Claude Bunzli - Structural and Photophysical Properties of Lanthanide Nitrate 1-1 Complexes with Planar Tridentate Nitrogen Ligands Analogous to 2,2'-6',2''-Terpyridine

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      Piguet,C., Williams,A.F., Bernardinelli,G., Moret,E.,   Bunzli,J.C.G. Helvetica Chimica Acta  1992 75 (5) 1697-1717

      Abstract: The ligand   2,6-bis(1-methylbenzimidazol-2-yl)pyridine (mbzimpy, 1) reacts   with Eu(III) to give [Eu(mbzimpy)(NO3)3(CH3OH)] [4] whose crystal   structure (EuC22H21N8O10, a = 7.658(3) angstrom, b = 19.136(2)   angstrom, c = 8.882 angstrom, beta = 104.07(1)-degrees,   monoclinic. P2(1), Z = 2) shows a mononuclear structure where   Eu(III) is ten-coordinate by a meridional tridentate mbzimpy   ligand, three bidentate nitrates, and one CH3OH molecule, leading   to a low-symmetry coordination sphere around the metal ion.   Essentially the same coordination is found in the crystal   structure of [Eu(obzimpy)(NO3)3] (8) (EuC35H45N8O9, a = 9.095(2)   angstrom, b = 16.624(2) angstrom, c = 26.198(6) angstrom, beta =   95.85(1)-degrees, monoclinic, P2(1)/c, Z = 4) obtained by   reaction of 2,6-bis(1-octylbenzimidazol-2-yl)pyridine (obzimpy.   2) with Eu(III). Detailed photophysical studies of crystalline   [Ln(mbzimpy)(NO3)3(CH3OH)] and [Ln(obzimpy)(NO3)3] complexes (Ln   = Eu, Gd, Tb, Lu) show that 1 and 2 display 1-pi-pi* and 3-pi-pi*   excited states very similar to those observed in   2,2':6',2''-terpyridine, leading to efficient ligand to Ln(III)   intramolecular energy transfer. Spectroscopic results show that   an extremely efficient mbzimpy-to-Eu(III) transfer occurs in   [Ln(mbzimpy)(NO3)3(CH3OH)] and, in the case of Tb(III), a   Tb(III)-to-mbzimpy back transfer is also implied in the   deactivation process. The origin of these peculiar effects and   the influence of ligand design by going from mbzimpy to obzimpy   are discussed. H-1-NMR and luminescence data indicate that the   structure found in the crystal is essentially maintained in   solution

      Address (URL): WOS:A1992JK61600022