N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic,Structural, and Luminescent Properties |
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Authors: | Amir Zaïm Dr Homayoun Nozary Dr Laure Guénée Dr Céline Besnard Dr Jean‐François Lemonnier Prof?Dr Stéphane Petoud Prof?Dr Claude Piguet |
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Institution: | 1. Department of Inorganic, Analytical, and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, 1211 Geneva 4 (Switzerland);2. Laboratory of Crystallography, University of Geneva, 24 quai E. Ansermet, 1211 Geneva 4 (Switzerland);3. Centre de Biophysique Moléculaire, CNRS UPR 4301, Rue Charles‐Sadron, 45071 Orléans Cedex 2 (France) |
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Abstract: | Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac?) and neutral, semi‐rigid, tridentate 2,6‐bis(benzimidazol‐2‐yl)pyridine ligands ( Lk ) to trivalent lanthanide atoms (LnIII). The solid‐state structures of Ln( Lk )(hfac)3] (Ln=La, Eu, Lu) showed that Ln(hfac)3] behaved as a neutral six‐coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron‐withdrawing trifluoromethyl substituents limited charge‐neutralization and favored cascade complexation with Lk ; 3) nine‐coordination was preserved for Ln( Lk )(hfac)3] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of Eu( Lk )(hfac)3], the ternary system LnIII/hfac?/ Lk is a promising candidate for the planned metal‐loading of preformed multi‐tridentate polymers. |
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Keywords: | lanthanides ligand effects nitrogen heterocycles photophysical properties thermodynamics |
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