Luminescence tuning of MOFs via ligand to metal and metal to metal energy transfer by co-doping of 2∞[Gd2Cl6(bipy)3]*2bipy with europium and terbium

The series of anhydrous lanthanide chlorides LnCl3, Ln=Pr–Tb, and 4,4'-bipyridine (bipy) constitute isotypic MOFs of the formula 2∞[Ln2Cl6(bipy)3]*2bipy. The europium and terbium containing compounds both exhibit luminescence of the referring trivalent lanthanide ions, giving a red luminescence for Eu3+ and a green luminescence for Tb3+ triggered by an efficient antenna effect of the 4,4'-bipyridine linkers. Mixing of different lanthanides in one MOF structure was undertaken to investigate the potential of this MOF system for colour tuning of the luminescence. Based on the gadolinium containing compound, co-doping with different amounts of europium and terbium proves successful and yields solid solutions of the formula 2∞[Gd2-x-yEuxTbyCl6(bipy)3]*2bipy (1–8), 0≤x, y≤0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4'-bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb3+ to Eu3+ is as well vital for the emission colour. However, no involvement of Gd3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity

Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

Biomimetic mineralization of metal-organic frameworks as protective coatings for biomacromolecules

Enhancing the robustness of functional biomacromolecules is a critical challenge in biotechnology, which if addressed would enhance their use in pharmaceuticals, chemical processing and biostorage. Here we report a novel method, inspired by natural biomineralization processes, which provides unprecedented protection of biomacromolecules by encapsulating them within a class of porous materials termed metal-organic frameworks. We show that proteins, enzymes and DNA rapidly induce the formation of protective metal-organic framework coatings under physiological conditions by concentrating the framework building blocks and facilitating crystallization around the biomacromolecules. The resulting biocomposite is stable under conditions that would normally decompose many biological macromolecules. For example, urease and horseradish peroxidase protected within a metal-organic framework shell are found to retain bioactivity after being treated at 80 °C and boiled in dimethylformamide (153 °C), respectively. This rapid, low-cost biomimetic mineralization process gives rise to new possibilities for the exploitation of biomacromolecules.Kang Liang, Raffaele Ricco, Cara M. Doherty, Mark J. Styles, Stephen Bell, Nigel Kirby, Stephen Mudie, David Haylock, Anita J. Hill, Christian J. Doonan, Paolo Falcar

Comportement de la Xonotlite Exposée aux Hautes Températures

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Comportement de la xonotlite exposée aux hautes températures

Afin de modéliser le comportement thermomécanique de matériaux dédiés à la protection incendie, l'étude de leur comportement thermophysique est mise en œuvre. Le produit composite étudié est essentiellement composé de xonotlite, un silicate de calcium hydraté renforcé par des fibres organiques de type cellulose. Différentes méthodes d'analyses sont utilisées pour suivre l'évolution de la structure du produit soumis à un incendie (T$\,{>}\,$1000$^{\circ}$C et présence de flammes) : mesures ATD/TG, diffraction des rayons X (température ambiante ou thermodiffraction). Les résultats de ces analyses sont croisés avec des visualisations MEB. L'analyse de l'évolution des phases cristallines associée à une évolution importante et rapide de température permet de comprendre comment le matériau supporte l'incendie. L'identification de ses conditions de ruine du produit découle de cette étude

Rational Design of Dual IR and Visible Highly Luminescent Light-Lanthanides-Based Coordination Polymers

International audienceA series of isostructural homo- and heterolanthanide coordination polymers of formula [Ln(dcpa)(HO)] with Ln = La-Gd have been obtained by reactions in water between the lightest lanthanide chlorides and the disodium salt of 4,5-dichlorophthalic acid (Hdcpa). They present particularly high thermal stability for coordination compounds (up to 400 °C). Their luminescent properties have been studied in detail. Interestingly an insensitivity to water coordination as well as a very strong effect of optical dilution is observed. Therefore, molecular alloys with very high lanthanum concentration have been prepared. Some of them present highly tunable and very intense luminescence. For example, to the best of our knowledge, [SmLa(dcpa)(HO)] presents one of the highest overall quantum yields measured so far for a Sm-based coordination compound ( = 9.2%), and [NdSmEuLa(dcpa)(HO)] is one of the brightest (12 Cd·m under 0.75 mW·cm UV flux) multiemissive visible and near-infrared lanthanide-coordination polymers reported to date

Lanthanide-based molecular alloys with hydroxyterephthalate: A versatile system

International audienceReactions in water between lanthanide chlorides and the disodium salt of 2-hydroxyterephthalic acid (H2hbdc) lead to six families of lanthanide-based coordination polymers depending on the lanthanide ion and the crystal growth method. Compounds that constitute family F1 have the general chemical formula [Ln(Hhbdc)(hbdc)·9H2O]∞ with Ln = La-Nd and have been obtained by slow evaporation. [Ln2(hbdc)3(H2O)6·4H2O]∞ with Ln = Sm-Eu constitute family F2 and have been obtained by solvothermal synthesis. Family F3 includes compounds, obtained by a solvothermal method, with the general chemical formula [Ln2(hbdc)3(H2O)4·4H2O]∞ with Ln = Ho-Lu plus Y and compounds obtained by slow diffusion through gels with Ln = Eu-Tb. [Ln(Hhbdc)(hbdc)(H2O)3·H2O]∞ with Ln = Tb-Dy have been obtained by solvothermal methods and constitute family F4. [Gd2(hbdc)3(H2O)8·6H2O]∞ (F5) has been obtained by slow evaporation. The last family (F6) includes compounds with the general chemical formula [Ln2(hbdc)3(H2O)8·2H2O]∞ with Ln = Nd-Tb that have been obtained by slow diffusion through gel media. Gd-Based micro-crystalline powders can be obtained by direct mixing of aqueous solutions of Gd3+ and hbdc2-. Unexpectedly, the micro-crystalline powder belongs to F5 when the lanthanide solution is added to the ligand one and to F6 when the opposite occurs. This phenomenon is also observed for the Tb- and/or Eu-based heterolanthanide coordination polymers. Their optical properties have been studied in detail

Origin of second-order transverse magnetic anisotropy in Mn12-acetate

The symmetry breaking effects for quantum tunneling of the magnetization in Mn-12-acetate, a molecular nanomagnet, represent an open problem. We present structural evidence that the disorder of the acetic acid of crystallization induces sizable distortion of the Mn(III) sites, giving rise to six different isomers. Four isomers have symmetry lower than tetragonal and a nonzero second-order transverse magnetic anisotropy, which has been evaluated using a ligand field approach. The result of the calculation leads to an improved simulation of electron paramagnetic resonance spectra and justifies the tunnel splitting distribution derived from the field sweep rate dependence of the hysteresis loops