25 research outputs found

    Distributive Nd-to-Yb Energy Transfer within Pure [YbNdYb] Heterometallic Molecules

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    Facile access to site-selective hetero-lanthanide molecules will open new avenues in the search of novel photophysical phenomena based on Ln-to-Ln′ energy transfer (ET). This challenge demands strategies to segregate efficiently different Ln metal ions among different positions in a molecule. We report here the one-step synthesis and structure of a pure [YbNdYb] (1) coordination complex featuring short Yb···Nd distances, ideal to investigate a potential distributive (i.e., from one donor to two acceptors) intramolecular ET from one Nd3+ ion to two Yb3+ centers within a well-characterized molecule. The difference in ionic radius is the mechanism allowing to allocate selectively both types of metal ion within the molecular structure, exploited with the simultaneous use of two β-diketone-type ligands. To assist the photophysical investigation of this heterometallic species, the analogues [YbLaYb] (2) and [LuNdLu] (3) have also been prepared. Sensitization of Yb3+ and Nd3+ in the last two complexes, respectively, was observed, with remarkably long decay times, facilitating the determination of the Nd-to-Yb ET within the [YbNdYb] composite. This ET was demonstrated by comparing the emission of iso-absorbant solutions of 1, 2, and 3 and through lifetime determinations in solution and solid state. The comparatively high efficiency of this process corroborates the facilitating effect of having two acceptors for the nonradiative decay of Nd3+ created within the [YbNdYb] molecule

    Luminiscent and Magnetic Tb-MOF Flakes Deposited on Silica

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    The synthesis of a terbium-based 2D metal-organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)2] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of tlf ⇡ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications

    Molecular Structure of Copper and μ-Oxodiiron Octafluorocorrole Derivatives: Insights into Ligand Noninnocence

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    Single-crystal X-ray structures were obtained for the copper and μ-oxodiiron complexes of 2,3,7,8,12,13,17,18-octafluoro-5,10,15-triphenylcorrole, hereafter denoted as Cu[F8TPC] and {Fe[F8TPC]}2O. A comparison with the crystal structures of other undecasubstituted Cu corroles, including those with H, Ar, Br, I, and CF3 as β-substituents, showed that the degree of saddling increases in the order: H ≲ F < Ar ≲ Br ≲ I < CF3. In other words, Cu[F8TPC] is marginally more saddled than β-unsubstituted Cu triarylcorroles, but substantially less saddled than Cu undecaarylcorroles, β-octabromo-meso-triarylcorroles, and β-octaiodo-meso-triarylcorroles, and far less saddled than Cu β-octakis(trifluoromethyl)-meso-triarylcorroles. As for {Fe[F8TPC]}2O, the moderate quality of the structure did not allow us to draw firm conclusions in regard to bond length alternations in the corrole skeleton and hence also the question of ligand noninnocence. The Fe–O bond distances, 1.712(8) and 1.724(8), however, are essentially identical to those observed for {Fe[TPFPC]}2O, where TPFPC3– is the trianion of 5,10,15-tris(pentafluorophenyl)corrole, suggesting that a partially noninnocent electronic structural description may be applicable for both compounds

    A Thorium Chalcogenolate Series Generated by Atom Insertion into Thorium–Carbon Bonds

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    A new thorium monoalkyl complex, Th­(CH<sub>2</sub>SiMe<sub>3</sub>)­(L<sub>3</sub>) (L = MeC­(N<sup><i>i</i></sup>Pr)<sub>2</sub>) (<b>2</b>), undergoes insertion of chalcogen atoms resulting in a series of thorium chalcogenolate complexes, Th­(ECH<sub>2</sub>SiMe<sub>3</sub>)­(L<sub>3</sub>) (E = S, SS, Se, Te; <b>5</b>–<b>8</b>). Complex <b>6</b> represents the first alkyl disulfide thorium species and illustrates the ability of <b>2</b> to undergo controllable, stoichiometric atom insertion. All complexes have been characterized by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy, FTIR, EA, and melting point, and in the case of <b>1</b>, <b>2</b>, and <b>4</b>–<b>8</b>, X-ray crystallography. Insertion was achieved by balancing the thermodynamic driving force of chalcogenolate formation versus the BDE of the pnictogen–chalcogen bond in the transfer reagent. Utilizing Me<sub>3</sub>NO as an oxygen atom transfer reagent led to C–H activation and SiMe<sub>4</sub> extrusion rather than oxygen atom insertion, resulting in the alkoxide complex Th­(OCH<sub>2</sub>NMe<sub>2</sub>)­(L<sub>3</sub>) (<b>4</b>)
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