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Bilbeisi R.A.,Abu Dhabi University | Olsen J.-C.,Indiana University Kokomo | Charbonniere L.J.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Trabolsi A.,Abu Dhabi University
Inorganica Chimica Acta | Year: 2014

Novelty, aesthetic appeal and the promise of a wide range of applications drive the current surge of interest in discrete metal-organic coordination complexes. This review covers achievements in the design, synthesis, characterization, and application of these multinuclear complexes in the years 2011-2013. Examples of their structural interconversion within dynamic combinatorial libraries are also presented. © 2014 Elsevier B.V. All rights reserved.

Brandel J.,University of Strasbourg | Lecointre A.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Kollek J.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Michel S.,University of Strasbourg | And 4 more authors.
Dalton Transactions | Year: 2014

The synthesis of ligand LTH8, based on a thiophene framework containing two bis(aminomethyldiphosphonate) functions in the ortho position to the central sulfur atom, is described, together with the characterization of the intermediate compounds. The physico-chemical properties of the ligand were first studied by means of potentiometry and UV-Vis absorption spectrophotometric titrations to determine its pK values. Six successive equilibrium constants were determined in aqueous solutions. The same means were then used to quantify the interactions of the ligand with Ni(II), Cu(II) and Zn(II). Following the conventional Irving-Williams trend, LT was shown to have the highest affinity towards Cu(II) (log K(CuLT) = 16.11(3)), while Zn(II) and Ni(II) showed similar values (log K(MLT) = 10.81(8) and 10.9(1), respectively), revealing a large selectivity of L T toward Cu(II). Based on a combination of UV-Vis absorption spectroscopy and EPR measurements as a function of pH, along with DFT calculations, the coordination behavior of the hard phosphonate, medium amino and soft thiophene entities are questioned regarding their coordination to the Cu atom. © the Partner Organisations 2014.

Charbonniere L.J.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Faulkner S.,University of Oxford | Platas-Iglesias C.,University of La Coruna | Regueiro-Figueroa M.,University of La Coruna | And 5 more authors.
Dalton Transactions | Year: 2013

Homodinuclear lanthanide complexes derived from a ligand featuring two DO3A chelating sites linked by a 4,4′-dimethyl-2,2′-bipyridyl spacer were prepared and characterized. The bipyridyl coordination site of 1 was used to introduce Ru(Bpy)2 and Re(CO)3Cl moieties, leading to the formation of heterometallic d-f2 complexes with general formulae [Ln2·1·Ru(Bpy)2]2+ (Ln = Nd, Eu, Tb, Yb and Lu) and [Ln2·1·Re(CO)3Cl] (Ln = Nd, Yb and Lu). The luminescence properties of the complexes were investigated by means of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy covering the visible and NIR regions. Both Ru and Re chromophores were shown to act as efficient sensitizers of the NIR emission of Yb and Nd in aqueous solutions. We also consider the unsaturated coordination spheres of the Ln cations in the Ln2·1 complexes, which form ternary complexes with bidentate anions without showing particular synergistic effects for polyanionic species. This journal is © 2013 The Royal Society of Chemistry.

Regueiro-Figueroa M.,University of La Coruna | Nonat A.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Rolla G.A.,University of Piemonte Orientale | Esteban-Gomez D.,University of La Coruna | And 5 more authors.
Chemistry - A European Journal | Year: 2013

Homodinuclear lanthanide complexes (Ln=La, Eu, Gd, Tb, Yb and Lu) derived from a bis-macrocyclic ligand featuring two 2,2',2''-(1,4,7,10- tetraazacyclododecane-1,4,7-triyl)triacetic acid chelating sites linked by a 2,6-bis(pyrazol-1-yl)pyridine spacer (H2L3) were prepared and characterized. Luminescence lifetime measurements recorded on solutions of the EuIII and TbIII complexes indicate the presence of one inner-sphere water molecule coordinated to each metal ion in these complexes. The overall luminescence quantum yields were determined (φ H 2O=0.01 for [Eu2(L3)] and 0.50 for [Tb2(L3)] in 0.01 M TRIS/HCl, pH 7.4; TRIS=tris(hydroxymethyl)aminomethane), pointing to an effective sensitization of the metal ion by the bispyrazolylpyridyl unit of the ligand, especially with Tb. The nuclear magnetic relaxation dispersion (NMRD) profiles recorded for [Gd2(L3)] are characteristic of slowly tumbling systems, showing a low-field plateau and a broad maximum around 30 MHz. This suggests the occurrence of aggregation of the complexes giving rise to slowly rotating species. A similar behavior is observed for the analogous GdIII complex containing a 4,4'-dimethyl-2,2'-bipyridyl spacer ([Gd2(L1)]). The relaxivity of [Gd2(L 3)] recorded at 0.5 T and 298 K (pH 6.9) amounts to 13.7 mM -1 s-1. The formation of aggregates has been confirmed by dynamic light scattering (DLS) experiments, which provided mean particle sizes of 114 and 38 nm for [Gd2(L1)] and [Gd2(L 3)], respectively. TEM images of [Gd2(L3)] indicate the formation of nearly spherical nanosized aggregates with a mean diameter of about 41 nm, together with some nonspherical particles with larger size. LnIII-based nanosized materials: A bis-macrocyclic ligand containing two 2,2',2''-(1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid chelating sites linked by a 2,6-bis(1H-pyrazol-1-yl)pyridine spacer forms binuclear complexes [Ln2(L)] giving stable nanosized aggregates in water with a mean size of about 40 nm (see figure). These aggregates provide a very efficient sensitization of EuIII, and particularly Tb III, and high relaxivities for the GdIII complex, which make them potential candidates as bimodal probes for optical and magnetic resonance imaging. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonat A.,Laboratoire dIngenierie Moleculaire Appliquee A lAnalyse | Regueiro-Figueroa M.,University of La Coruna | Esteban-Gomez D.,University of La Coruna | De Blas A.,University of La Coruna | And 3 more authors.
Chemistry - A European Journal | Year: 2012

Ligand L, based on two do3a moieties linked by the methylene groups of 6,6'-dimethyl-2,2'-bipyridine, was synthesized and characterized. The addition of Ln salts to an aqueous solution of L (0.01 M Tris-HCl, pH 7.4) led to the successive formation of [LnL] and [Ln 2L] complexes, as evidenced by UV/Vis and fluorescence titration experiments. Homodinuclear [Ln 2L] complexes (Ln=Eu, Gd, Tb, Yb, and Lu) were prepared and characterized. The 1H and 13C NMR spectra of the Lu and Yb complexes in D 2O solution (pD=7.0) showed C 1 symmetry of these species in solution, pointing to two different chemical environments for the two lanthanide cations. The analysis of the chemical shifts of the Yb complex indicated that the two coordination sites present square antiprismatic (SAP) coordination environments around the metal ions. The spectroscopic properties of the [Tb 2L] complex upon ligand excitation revealed conventional behavior with τ H2O=2.05(1) ms and φ H2O=51 %, except for the calculation of the hydration number obtained from the luminescent lifetimes in H 2O and D 2O, which pointed to a non-integer value of 0.6 water molecules per Tb III ion. In contrast, the Eu complex revealed surprising features such as: 1) the presence of two and up to five components in the 5D 0→ 7F 0 and 5D 0→ 7F 1 emission bands, respectively; 2) marked differences between the normalized spectra obtained in H 2O and D 2O solutions; and 3) unconventional temporal evolution of the luminescence intensity at certain wavelengths, the intensity profile first displaying a rising step before the occurrence of the expected decay. Additional spectroscopic experiments performed on [Gd 2-xEu xL] complexes (x=0.1 and 1.9) confirmed the presence of two distinct Eu sites with hydration numbers of 0 (site I) and 2 (site II), and showed that the unconventional temporal evolution of the emission intensity is the result of an unprecedented intramolecular Eu-to-Eu energy-transfer process. A mathematical model was developed to interpret the experimental data, leading to energy-transfer rates of 0.98 ms -1 for the transfer from the site with q=0 to that with q=2 and vice versa. Hartree-Fock (HF) and density functional theory (DFT) calculations performed at the B3LYP level were used to investigate the conformation of the complex in solution, and to estimate the intermetallic distance, which provided Förster radii (R 0) values of 8.1 Å for the energy transfer from site I to site II, and 6.8 Å for the reverse energy transfer. These results represent the first evidence of an intramolecular energy-transfer equilibrium between two identical lanthanide cations within a discrete molecular complex in solution. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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