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Three molecular structures, each containing three different lanthanide(III) centres, have been prepared by coupling three kinetically inert lanthanide(III) complexes in an Ugi reaction. These 2 kDa molecules were purified by dialysis and characterised by NMR and luminescence techniques. The photophysical properties of these heterotrimetallic complexes were investigated and are discussed by comparison with simpler, but related, heterodimetallic compounds. It was found that an aminonaphthalene unit inhibits the sensitisation of terbium, and that the spatial arrangement of the chromophores and lanthanide(III) centres in these molecules inhibits the efficient sensitisation of europium. We conclude that the intramolecular collisions required for efficient Dexter energy transfer from the sensitiser to the lanthanide(III) centre can be prevented by steric congestion. [ABSTRACT FROM AUTHOR]

Lanthanide complexes of tetrapicolyl cyclen displayed remarkably high affinities for fluoride (log K≈5) in water, and were shown to form 1:1 complexes. The behaviour of these systems can be rationalised by changes to the magnitude of the crystal-field parameter [ABSTRACT FROM AUTHOR]

Self-assembly of a range of carboxylic acids (benzoic acid, dinicotinic acid, nicotinic acid, and isophthalic acid) with the europium complex of 5-nitro-α,α′-bis(DO3Ayl)- m-xylene (where DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) has been explored to establish the thermodynamics of binding in a range of solvent systems and in a range of aqueous buffer solutions. In this system, profound effects are observed as a consequence of competition by the hydroxide ion, which outcompetes even dinicotinate at high pH. In the case of isophthalate, which binds most strongly, and dinicotinate, both enthalpic and entropic contributions to binding have been identified. The europium complex with 5-nitro-α,α′-bis(DO3Ayl)- m-xylene is found to have a solution structure significantly different from the related europium complex of 5-amino-α,α′-bis(DO3Ayl)- m-xylene. It is found that phosphate binds strongly to the europium complex of the nitro derivate but not to the europium complex of amino derivative. Lactate, citrate, and pyruvate also bind strongly to 5-nitro-α,α′-bis(Eu⋅DO3Ayl)- m-xylene, and it is concluded that the solution structure of this binuclear lanthanide complex is significantly different from that of the amino-substituted complex. [ABSTRACT FROM AUTHOR]

The association between dinuclear lanthanide complexes and dicarboxylate guests has been studied to elucidate the factors that influence the self-assembly of these ternary structures. The self-assembly between α,α′-bis(Eu ·DO3A)- m-xylyl (H3DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) host complexes and dicarboxylate guests and the association of a dinicotinate guest and an α,α′-bis(Ln ·DO3A)-3,5-dimethylpyridine host in water were demonstrated, and the study of lanthanide-mediated self-assembly and the methods used to investigate the self-assembly are discussed in detail. Furthermore, the self-assembly has been extended to involve five ions from across the lanthanide series, namely, Nd3+, Eu3+, Tb3+, Dy3+ and Yb3+. The self-assembly process, measured by the association constant Ka, is independent of the nature of the lanthanide centre but it is highly solvent dependent. The association constants between a given host-guest pair vary by several orders of magnitude when determined in methanol, methanol/water and water. We conclude that although a lanthanide-centred self-assembly process can be controlled through design, the strength of the association can only be rationalised after the event. The multiple parameters involved in the determination of the value of the association constant appear to be dominated by the solvation contribution to a degree that specific and general solvation has to be understood before we can fully rationalise the association between dinuclear lanthanide complexes and dicarboxylate guests. [ABSTRACT FROM AUTHOR]

A study of the anion-binding properties of three structurally related lanthanide complexes, which all contain chemically identical anion-binding motifs, has revealed dramatic differences in their anion affinity. These arise as a consequence of changes in the substitution pattern on the periphery of the molecule, at a substantial distance from the binding pocket. Herein, we explore these remote substituent effects and explain the observed behaviour through discussion of the way in which remote substituents can influence and control the global structure of a molecule through their demands upon conformational space. Peripheral modifications to a binuclear lanthanide motif derived from α,α′-bis(DO3 Ayl)- m-xylene are shown to result in dramatic changes to the binding constant for isophthalate. In this system, the parent compound displays considerable conformational flexibility, yet can be assumed to bind to isophthalate through a well-defined conformer. Addition of steric bulk remote from the binding site restricts conformational mobility, giving rise to an increase in binding constant on entropic grounds as long as the ideal binding conformation is not excluded from the available range of conformers. [ABSTRACT FROM AUTHOR]

Luminescence spectroscopy provides a window into conformational space and its influence on the anion binding properties of a series of binuclear lanthanide complexes. Bulky remote substituents are shown to have a profound influence on the affinity of such complexes for a given guest. For more information see the Full Paper by T. J. Sørensen, S. Faulkner et al. on page 16566 ff. [ABSTRACT FROM AUTHOR]

Abstract: The luminescent Pt(II) complex [Pt(4,4′- t Bu2-bipy){CC-(5-pyrimidinyl)}2] (1) was prepared by coupling of [Pt(4,4′- t Bu2-bipy)Cl2] with 5-ethynyl-pyrimidine, and contains two pyrimidinyl units pendant from a Pt(II) bipyridyl diacetylide core; it shows luminescence at 520nm which is typical of Pt(II) luminophores of this type. Reaction with [Ln(hfac)3(H2O)2] (hfac=anion of hexafluoroacetylacetone) affords as crystalline solids the compounds [1 ·{Ln(hfac)3(H2O)}{Ln(hfac)3(H2O)2}] (Ln=Nd, Gd, Er, Yb), in which the {Ln(hfac)3(H2O)} unit is coordinated to one pyrimidine ring via an N atom, whereas the {Ln(hfac)3(H2O)2} unit is associated with two N atoms, one from each pyrimidine ring of 1, via N⋯HOH hydrogen-bonding interactions involving the coordinated water ligands on the lanthanide centre. Solution spectroscopic studies show that the luminescence of 1 is partly quenched on addition of [Ln(hfac)3(H2O)2] (Ln=Er, Nd) by formation of Pt(II)/Ln(III) adducts in which Pt(II)→Ln(III) photoinduced energy-transfer occurs to the low-lying f–f levels of the Ln(III) centre. Significant quenching occurs with both Er(III) and Nd(III) because both have several f–f states which match well the 3MLCT emission energy of 1. Time-resolved luminescence studies show that Pt(II)→Er(III) energy-transfer (7.0×107 M−1) is around three times faster than Pt(II)→Nd(III) energy-transfer (≈2×107 M−1) over the same distance because the luminescence spectrum of 1 overlaps better with the absorption spectrum of Er(III) than with Nd(III). In contrast Yb(III) causes no significant quenching of 1 because it has only a single f–f excited level which is a poor energy match for the Pt(II)-based excited state. [Copyright &y& Elsevier]