Bimetallic Lanthanide Complexes Derived from Macrocycle‐Appended m‐Xylyl Derivatives: Synthesis and Spectroscopic Properties

Abstract

Dedicated to Professor Jean-Claude Bünzli on the occasion of his 65th birthday.A series of bimetallic lanthanide complexes was prepared from a bimacrocyclic system in which two DO3A units are linked by a m-xylyl unit appended with either a NO 2 or an NH 2 group (DO3A ¼ 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). The Nd-, Eu-, Tb-and Yb-complexes were all luminescent: time-resolved studies indicated that the lipophilic xylyl group restricts close approach of H 2 O to the metal centre.Introduction. -Lanthanide complexes have been widely used in imaging and assay applications for many years, particularly as a consequence of the widespread application of luminescent complexes in ultrasensitive bioassays [1] and of Gdcomplexes as magnetic-resonance-imaging (MRI) contrast agents [2]. Luminescence from lanthanide complexes is long-lived as a consequence of the forbidden nature of ff transitions, meaning that time-gating techniques can be used to distinguish long-lived luminescence from fluorescent background signals [3]. However, the forbidden nature of f -f transitions also means that lanthanide ions have very low extinction coefficients, so that direct excitation requires the use of high-intensity light sources [4]: this disadvantage can be overcome by using sensitising chromophores with large extinction coefficients. Such excitation is normally mediated by the triplet state [5] via both Fçrster [6] and Dexter [7] mechanisms, though other routes have also been implicated [8]. The energy of the emissive state of the lanthanide determines which chromophores can be used and also has a considerable impact upon the luminescence lifetime and quantum yield, since the sensitising donor state must be significantly higher in energy than the emissive state of the lanthanide to avoid back energy transfer, and since nonradiative quenching of the emissive state occurs most readily for ions with lowenergy emissive states (i.e., those that emit light in the near-IR part of the spectrum). This means that, although Eu-and Tb-complexes have high luminescence quantum yields when used with appropriate chromophores, the choice of chromophore is restricted to those which absorb in the UV, or at the blue edge of the VIS spectrum [9]. By contrast, Yb and Nd can be used with a wide range of sensitisers, including those

Using Remote Substituents to Control Solution Structure and Anion Binding in Lanthanide Complexes

“…[16] All three of these molecules contain the same m-xylyl bridged binuclear europium complex. [17] In the case of 1, this fragment has already been shown to bind to isophthalate in aqueous buffers and methanol/water solvent mixtures. [15a, 15b] The approach used to achieve the synthesis of these compounds relies upon the kinetic stability of the complexes 1 and 4, which has already been amply demonstrated through their use in preparing lanthanide arrays.…”

Thermodynamics of Self‐Assembly of Dicarboxylate Ions with Binuclear Lanthanide Complexes

“…5‐nitro‐α,α′‐(DO3Ayl)‐ m ‐xylene (H 6 ⋅ 1 ) and its binuclear europium complex (Eu 2 ⋅ 1 ) were prepared as previously described . Although this ligand was among the first m ‐xylyl‐bridged bismacrocycles to be prepared, we have previously only carried out very limited studies upon the binding of anionic guest species beyond establishing the affinity for dinicotinate in tris(hydroxymethyl)aminomethane (TRIS) buffer .…”

“…5-nitro-a,a'-(DO3Ayl)-m-xylene (H 6 ·1)a nd its binuclear europium complex( Eu 2 ·1)w ere prepared as previously described. [34] Although this ligand was amongt he first m-xylyl-bridgedb ismacrocycles to be prepared, we have previously only carried out very limited studies upon the bindingo fa nionic guest speciesb eyonde stablishing the affinity for dinicotinate in tris(hydroxymethyl)aminomethane( TRIS) buffer. [28] In this study, we report am uch broader range of data and establish the affinity for four different anions, and define the bindingi nm ethanolic anda queous media at arange of temperatures.…”

“…It is worth noting that the inner sphere hydration (where q is the number of inner sphere solvent molecules) of Eu 2 ⋅ 1 is significantly greater than that of Eu 2 ⋅ 2 ( q (Eu 2 ⋅ 1 )=1.2 and q (Eu 2 ⋅ 2 )=0.8, see Ref. ). As such, Eu 2 ⋅ 1 would be expected to display a greater affinity for phosphate, since phosphate can act as a bidentate donor at one of the lanthanide centres.…”

5f-Element complexes with a p-tert-butylcalix[4]arene bearing phosphinoyl pendant arms: Separation from rare earths and structural studies

“…Therefore, complexes with weakly a-emitting, long half-life radio-elements such as uranium [2][3][4][5][6] and tetravalent thorium [7] have been the most studied while lanthanide ions (Ln), in an indirect way, have afforded knowledge on the chemical behavior of trivalent actinides [8,9]. Thorium coordination chemistry is also well documented, both with respect to hydration and hydrolysis [10], complexes with oxygen-and nitrogen-donor ligands [7], macrocyclic complexes [11][12][13], and even quadruple-stranded helicates [14].…”