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Title

Structural and Photophysical Properties of Lanthanide Nitrate 1:1 Complexes with Planar Tridentate Nitrogen Ligands Analogous to 2,2′:6′,2′′-Terpyridine

Authors
Moret, Emmanuel
Bünzli, Jean-Claude G.
Published in Helvetica Chimica Acta. 1992, vol. 75, no. 5, p. 1697-1717
Abstract The ligand 2,6‐bis(1‐methylbenzimidazol‐2‐yl)pyridine (mbzimpy, 1) reacts with EuIII to give [Eu(mbzimpy)(NO₃)₃(CH₃OH)] [4] whose crystal structure (EuC₂₂H₂₁N₈O₁₀, a = 7.658(3) Å, b = 19.136(2) Å, c = 8.882 Å, β = 104.07(1)°, monoclinic, P2₁, Z = 2) shows a mononuclear structure where EuIII 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 metalion. Essentially the same coordination is found in the crystal structure of [Eu(obzimpy)(NO₃)₃] (8) (EuC₃₅H₄₅N₈O₉, a = 9.095(2) Å, b = 16.624(2) Å, c = 26.198(6) Å, β = 95.85(1)°, monoclinic, P2₁/c, Z = 4) obtained by reaction of 2,6‐bis(1‐octylbenzimidazol‐2‐yl)pyridine (obzimpy, 2) with EuIII. 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 ¹ππ* and ³ππ* excited states very similar to those observed in 2,2′:6′,2″‐terpyridine, leading to efficient ligand to LnIII intramolecular energy transfer. Spectroscopic results show that an extremely efficient mbzimpy‐to‐EuIII transfer occurs in [Ln(mbzimpy)(NO₃)₃(CH₃OH)] and in the case of TbIII, a TbIII‐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. ¹H‐NMR and luminescence data indicate that the structure found in the crystal is essentially maintained in solution.
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Other version: http://doi.wiley.com/10.1002/hlca.19920750523
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PIGUET, Claude et al. Structural and Photophysical Properties of Lanthanide Nitrate 1:1 Complexes with Planar Tridentate Nitrogen Ligands Analogous to 2,2′:6′,2′′-Terpyridine. In: Helvetica Chimica Acta, 1992, vol. 75, n° 5, p. 1697-1717. doi: 10.1002/hlca.19920750523 https://archive-ouverte.unige.ch/unige:117895

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