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N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate) 3 ] Units: Thermodynamic, Structural, and Luminescent Properties
Author(s) -
Zaïm Amir,
Nozary Homayoun,
Guénée Laure,
Besnard Céline,
Lemonnier JeanFrançois,
Petoud Stéphane,
Piguet Claude
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102827
Subject(s) - chemistry , lanthanide , ternary operation , crystallography , pyridine , luminescence , dissociation (chemistry) , ligand (biochemistry) , stereochemistry , inorganic chemistry , ion , medicinal chemistry , organic chemistry , materials science , computer science , programming language , biochemistry , receptor , optoelectronics
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 ( L k ) to trivalent lanthanide atoms (Ln III ). The solid‐state structures of [Ln( L k )(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 L k ; 3) nine‐coordination was preserved for [Ln( L k )(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( L k )(hfac) 3 ], the ternary system Ln III /hfac − / L k is a promising candidate for the planned metal‐loading of preformed multi‐tridentate polymers.