Europium ligand complexes

Carboxylbenzoyl and 1-carboxyl 8-naphthoyl partially substituted polystyrene have teen prepared by the Friedel Crafts reaction between polystyrene and the corresponding dicarboxylic anhydrides. Rare earth (Europium-III) complexes of these polymer based ligands have been obtained [20] (Fig. 10). 

As it is well known, sensitization of Ln-centered luminescence can be achieved via an intramolecular energy transfer upon excitation of organic ligands, instead of using direct excitation of the weak Lnm absorption bands. This phenomenon now called antenna effect or luminescence sensitization has first been observed in 1942 by Weissman for europium(III) complexes formed with salicylaldehyde and with /3-diketonates, more particularly benzoyl-acetonate (ba, 48a), dibenzoylmethanate (dbm, 48b) and wieta-nitrobenzoylacctonatc (47a, fig. 41) (Weissman, 1942). 

Mononuclearity in Ln(II) CH-alkoxides has not yet been proven by X-ray crystallography [28,55,56]. The dimeric heteroleptic complex (Yb[N(SiMe3)2] ( -tritox) 2 established the alkoxide ligand as the bridging moiety [28]. Mono-europium(II) complexes with tri-fert-butoxygermanate-, -Stannate and -plum-bate ligands were reported and Eu [Sn(OtBu)3]2 was characterized by X-ray structure analysis (Table 2) [55b]... 

These assays are based upon the use of a europium or terbium chelate (a transition metal-ligand complex displaying long-lived fluorescent properties) and labeled anti-phosphopeptide or anti-phos-photyrosine antibodies that can bind to phosphorylated peptides. The antibodies are usually labeled... 

Shao, N., Jin, J., Wang, G, et al. (2008) Europium(lll) complex-based luminescent sensing probes for multi-phosphate anions modulating selectivity by ligand choice. Chemical Communications, 1127-1129. 

Europium (III) complexes of other -diketones. The complexes, (C2H5)3NH[Eu(hfa)4] and (CH3)4N[Eu(hfa)4], were synthesized by the methods described by Melby, Rose, Abramson, and Caris (15). The tris bidentate chelates, Eu(tfa)3 2H2O, and Eu(tta)3 3H2O, were obtained commercially (Distillation Products Industries) and were analyzed prior to use. The ligands corresponding to the various symbols are as follows tfa—l,l,l-trifluoro-2,4-pentanedionate, hfa—1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, and tta—4,4,4-trifluoro-1 (2-thienyl) -1,3-butanedionate. 

The differences observed in the temperature dependences of luminescence for europium and terbium(III) clathrochelates can also be due to the absence of back energy transfer from encapsulated Eu cation to the clathrochelate ligand. The expression for the rate constant of metal-to-ligand back transfer contains the AE value, which is the energy difference between the triplet level of the bipyridine fragment and the metal ion phosphorescence level. The back transfer rate for the europium (III) ion is much less than that for the terbium(III) ion. This process is essential for the terbium(III) ion, and this is confirmed by differences in the temperature dependence of excited-state lifetimes for europium and terbium (III) clathrochelates in D5O the luminescence of the terbium(III) complex at 77 K is approximately an order of magnitude higher than that at 300 K, whereas for the europium(III) complex, it does not depend on temperature. 

The fluorescence properties of several europium and samarium ) -diketonates have been measured and assignments of the transitions made. Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to fluoresce. The luminescence of the heptafluoroheptane-2,4-dione complexes of Sm, Eu, and Tb has been measured in dilute ethanol at pH8 and 610nm mixed-ligand complexes with 1,10-phenanthroline exhibited an enhanced luminescence. Photolysis of the Tb chelate of 2,2,6,6-tetramethylheptane-3,5-dione has been examined at 311 nm in various alcohols, and loss of one -diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 

The effect of varying alkyl substituents at the two and six positions on the bridging ability of the aryloxide ligands in europium(II) complexes... 

At one extreme, a derivative free of coordination by water or anions has been prepared by the reaction of europium metal with NOBF4 in dry acetonitrile (Albin et al., 1983). The resulting Eu(CH3CN) (Y) species (Y = BF4, PF ) reacts further with two equivalent ionophoric ligands to give bis(ligand) complexes. 

Simple ligand association is commonly used especially for metal complexes with low electron counts where stability benefits from additional electron density. With the first NHC-samarium complexes, Arduengo reported that coordination of IMe to a europium(III) complex with a tris-(2,2,6,... 

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