Helicates lanthanide

In the study of the mechanism of formation of heUcates (Fig. 9.6) Ehlabiri et al. [34,35] have demonstrated that the self-assembly mechanism is mainly governed by cooperative electrostatic interactions between the metal and the Ugand 4. The initial coordination of two 

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Martin, N. Biinzli, J.-C. G. McKee, V. Piguet, C. Hopfgartner, G. Self-assembled dinuclear lanthanide helicates substantial luminescence enhancement upon replacing terminal benzimidazole groups by carboxamide binding units. Inorg. Chem. 1998, 37, 577-589. 

Elhabiri, M. Scopelliti, R. Biinzli, J.-C. G. Piguet, C. Lanthanide helicates self-assembled in water a new class of highly stable and luminescent dimetallic carboxy-lates. J. Am. Chem. Soc. 1999,121,10747-10762. 

Bocquet, B. Bernardinelli, G. Ouali, N. Floquet, S. Renaud, F. Hopfgartner, G. Piguet, C. The first self-assembled trimetallic lanthanide helicate different coordination sites in symmetrical molecular architectures. Chem. Commun. 2002, 930-931. 

Claude Piguet and Jean-Claude G. Biinzli, Self-Assembled Lanthanide Helicates From Basic Thermodynamics to Applications 301... 

The photophysical properties of the triple-stranded dimetallic helicates [Ln2(41)3] (Ln=Nd, Sm, Dy, Yb) were investigated in water and D2O solutions by Biinzil and coworkers [64]. Lanthanide-centered luminescence is well sensitized in the triple stranded homodimetallic helicate complexes. The absolute quanmm yield of the ligand-centered luminescence decreases dramatically upon formation of the lanthanide helicates because of a significant enhancement... 

Self-Assembled Lanthanide Helicates From Basic Thermodynamics to Applications... 

Modeling lanthanide helicate self-assembly in solution... 

FIGURE 13 Formation of (A) a binuclear saturated triple-stranded lanthanide helicate and (B) a binuclear unsaturated double-stranded side-by-side lanthanide complex (redrawn after Martin et al., 1998). 

A similar limitation has been recently reported for the synthesis of unsaturated triple-stranded binuclear lanthanide helicates with bis-bidentate acylpyrazolone ligand strands and some analogues of bis- S-diketonate ligands, for which only the ethyl spacer was found to form the targeted helical complex (Semenov et al., 2008). 

FIGURE 15 Top oxygen-donor ligands used by Basset et al. (2004) and Goodgame et al. (1993). Bottom tridentate 2,6-disubstituted pyridines used as binding units for the design of lanthanide helicate since 1992. 

FIGURE 40 Correlations between the symmetry of the segmental multitridentate ligands and the nature of the final lanthanide helicates. 

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