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

Published inHelvetica Chimica Acta, vol. 75, no. 5, p. 1697-1717
Publication date1992
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.

Citation (ISO format)
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
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