58 research outputs found
A Permanently Porous Yttrium–Organic Framework Based on an Extended Tridentate Phosphine Containing Linker
No full textThe metal–organic framework [Y(tbpp)]·nDMF (1) was synthesized from yttrium(III) nitrate and the tritopic linker tris(4′-carboxy[1,1′-biphenyl]-4-yl)phosphine (H3tbpp). The distance between the coordinating atoms of the carboxylate groups of the extended tridentate phosphine linker is more than 1.8 nm, resulting in an average pore dimension of 0.9 nm in the noninterpenetrated metal–organic framework. The material exhibits high thermal stability and permanent porosity after removal of guest molecules from the one-dimensional pore system. The desolvated compound adsorbs nitrogen, argon, hydrogen, and carbon dioxide. Favorable adsorption of CO2 over N2 is predicted using ideal adsorbed solution theory (IAST). The isosteric enthalpies of adsorption of H2 and CO2 of −7 and −22 kJ mol–1, respectively, are representative for metal−organic frameworks with no accessible strong host–guest binding sites, despite the bifunctional nature of the organic ligand. The absence of strong specific adsorption sites was confirmed by in situ powder synchrotron X-ray diffraction of the reversible isobaric CO2 sorption process. Analysis of the diffraction data indicates that the CO2 molecules in the pores are disordered and nonlocalized. Despite this, it was possible to quantify the evolution of the occupation of the pores. CO2 is adsorbed at an approximately constant below 320 K from 10% loading to full capacity at 195 K.acceptedVersio
The iron member of the CPO-27 coordination polymer series: Synthesis, characterization, and intriguing redox properties
No full textThe microporous coordination polymer CPO-27-Fe was synthesized from iron salts and 2,5-dihydroxyterephthalic acid by microwave assisted solvothermal synthesis. The crystal structures of the as-synthesized compounds were determined by Rietveld refinement from powder X-ray diffraction data using synchrotron radiation, revealing a honeycomb-type framework, isostructural to the other compounds in the CPO-27-M series. Exposure to oxygen was found to have pronounced effects on the material, like change of color, band gap, and structural details which we associate with oxidation of the iron(II) in the M2(dhtp) framework to iron(III). XPS measurements confirm the presence of iron in these oxidation states in the respective compounds. The desolvation process of CPO-27-Fe was investigated using variable temperature powder X-ray diffraction and mass spectrometry. CPO-27-Fe passes through several phase transitions when heated up during which it reversibly changes between oxidation states +2 and +3, remaining in divalent state in the empty framework structure Fe2(dhtp) in the last crystalline phase. These measurements also indicate that methanol contained in the pore after synthesis is transformed into formaldehyde during the heating process, potentially making CPO-27-Fe a viable catalyst in redox processes. The effect of the extraordinary high concentration of accessible open metal sites in the desolvated CPO-27-Fe was investigated by gas adsorption experiments using hydrogen, carbon dioxide and oxygen. Oxygen adsorption was reversible at low temperatures, but exposure to oxygen at room temperature led to blocking of the open metal site and partial deconstruction of the framework. Significantly larger amounts of oxygen than nitrogen are adsorbed at room temperature
Variability in the formation and framework polymorphism of metal-organic frameworks based on yttrium(III) and the bifunctional organic linker 2,5-dihydroxyterephthalic acid
No full textDepending on the solvothermal reaction conditions, we obtained three different metal‐organic frameworks with yttrium(III) as metal component and 2,5‐dihdyroxyterepthalic acid (H4dhtp) as bifunctional organic linker: Y2(H2dhtp)3(dmf)4·(dmf)2 (CPO‐29) contains dinuclear, paddle‐wheel like inorganic secondary building units (SBUs) connected by the organic linker to a network with α‐Po topology, while Y2(H2dhtp)(dhtp)(dmf)2 (CPO‐30) and Y2(H2dhtp)(dhtp)(dmf)2(H2O)2·(H2O)4 (CPO‐31) contain one‐dimensional inorganic SBUs that differ in how the half‐ and fully deprotonated ligands are connected to and arranged around them. Only the carboxylic acid groups of the organic linker are deprotonated in CPO‐29, while CPO‐30 and CPO‐31 contain both 2,5‐dihydroxyterephthalate (H2dhtp2–) linkers and fully deprotonated 2,5‐dioxidoterephthalate (dhtp4–) linkers. All three compounds contain large volumes filled with solvent, but we were able to demonstrate permanence of porosity only for CPO‐30. Variable temperature powder X‐ray diffraction reveals that CPO‐29 and CPO‐31 undergo discontinuous phase transitions upon heating, and the flexibility of the framework structure indicated by these might be the reason for the inability to access the pore volume. Desolvated CPO‐30 and CPO‐31 are polymorphs, whose network structures differ in whether the H2dhtp2– and dhtp4– linkers are located in cis or trans arrangement around the inorganic SBU.publishedVersio
Variation of desolvation behavior in two isostructural metal–organic frameworks based on a flexible, racemic bifunctional organic linker
No full textA racemic mixture of the chiral ligand 4,4′-(1,2-dihydroxyethane-1,2-diyl)dibenzoic acid was used to prepare two isostructural metal–organic frameworks, CPO-49-Zn and CPO-49-Mn, which contain coordinated solvent molecules at the metal site. The compounds showed different behavior upon desolvation. The dissociation of the solvent molecule from the metal site leads to a single-crystal-to-single-crystal transformation. In CPO-49-Zn, a change of coordination geometry from trigonal bipyramidal to tetrahedral occurs at the zinc atom. In CPO-49-Mn, a rearrangement of coordination mode of a carboxylate group occurs instead, leading to a 4+1 coordination of the manganese cation in the form of a capped distorted tetrahedron. N2 gas adsorption confirms that both desolvated structures are permanently porous. The behavior of the compounds upon heating has also been studied using variable temperature powder X-ray diffraction. The presence of a coordinated solvent molecule in the as-synthesized structures indicates the possibility to access the metal cation with reactive substrates. Both materials were evaluated in the catalytic oxidation of styrene. CPO-49-Mn showed significantly higher conversion than the CPO-49-Zn material.acceptedVersio
Dimethyl 3,3′-dimethoxybiphenyl-4,4′-dicarboxylate
No full textIn the title compound, C18H18O6, the biphenyl moiety is twisted with a dihedral angle of 29.11 (10)°. The carbomethoxy groups form C—C—C—O torsion angles of −18.3 (3) and −27.7 (3)° with the attached rings, as a result of steric hindrances from the nearby methoxy groups. In the absence of stacking interactions and with no H...O contacts shorter than 2.7 Å, the packing is dominated by weaker van der Waals interactions
Methyl 5-iodo-2-methoxybenzoate
No full textIn the title compound, C9H9IO3, the molecules are close to planar [maximum deviation from benzene ring plane = 0.229 (5) Å for the methyl carboxylate C atom] with the methyl groups oriented away from each other. In the crystal, molecules form stacked layers parallel to the ab plane, where every layer has either the iodine or methoxy/methyl carboxylate substituents pointing towards each other in an alternating fashion
Modification of Network and Pore Dimensionality in Metal–Organic Frameworks Containing a Secondary Phosphine Functionality
No full textThree new metal-organic frameworks containing a triphenylphosphine moiety, namely [Zn3(tpp)2(DMF)2]·nDMF (1), [Zn3(tpp)2(4,4’-bipy)2]·nDMF (2) and [Zn3(tpp)2(3,3’-bipy)]·nDMF (3), were synthesized using 4,4',4''-phosphanetriyltribenzoic acid (H3tpp) as a tritopic tridentate linker. The absence or presence of additional N-donor linker molecules in the reaction mixture directed the formation of (3,6)-c layered, (3,8)-c pillared layered or (3,4,6)-c frameworks. Compound 1 is composed of a trinuclear zinc secondary building unit (SBU) and the tpp3- anion arranged in a layered (3,6)-c network with kgd topology. There are guest DMF molecules coordinated to the terminal Zn atoms of the trinuclear inorganic SBU. The addition of the neutral N-donor molecules 3,3’-bipyridine (3,3’-bipy) and 4,4’-bipyridine (4,4’-bipy) as second organic linker molecule lead to an increase of dimensionality of the networks. Compound 2 is a (3,4,6)-nodal three-dimensional MOF. Its structure consists of two equivalent interpenetrated nets with the point symbol (52·64)(52·6)2(54·66·72·8·92) with solvent filled pockets. The free electron pair of phosphorus atom of the triphenylphosphine moiety is pointing towards the 0-dimensional pores. The structure of 3 can be described as layers of 1 which are connected by additional 3,3’-bipyridine as pillar into a three-dimensional (3,8)-c network with the point symbol (43)2(46·618·84). The non-interpenetrated structure of 3 contains a solvent filled three-dimensional pore system. All three materials exhibit uptake of CO2 at 195 K after removal of the guest DMF molecules. It is particularly surprising for 2, with its 0-dimensional pores in the single crystal structure and absence of N2 adsorption at 77 K. 3 showed a large gate opening effect for CO2 adsorption at 195 K.acceptedVersio
Measurement of the Xi(-)(b) and Omega(-)(b) baryon lifetimes
No full textUsing a data sample of pp collisions corresponding to an integrated luminosity of 3 fb−1, the Ξ−b and Ω−b baryons are reconstructed in the Ξ−b → J/ψΞ− and Ω−b → J/ψΩ− decay modes and their lifetimes measured to be
τ(Ξ−b) = 1.55+0.10−0.09 (stat) ± 0.03 (syst) ps,
τ(Ω−b) = 1.54+0.26−0.21 (stat) ± 0.05 (syst) ps.
These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions
Effective lifetime measurements in the B-s(0) -> K+K-, B-0 -> K+pi(-) and B-s(0) -> pi K-+(-) decays
No full textMeasurements of the effective lifetimes in the View the MathML source, B0→K+π− and View the MathML source decays are presented using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance.
This is the most precise determination to date of the effective lifetime in the View the MathML source decay and provides constraints on contributions from physics beyond the Standard Model to the View the MathML source mixing phase and the width difference ΔΓs
Measurement of the CP-violating phase phi(s) in (B)over-bar(s)(0) -> J / psi pi(+)pi(-) decays
No full textThe mixing-induced CP -violating phase ϕs in View the MathML source and View the MathML source decays is measured using the J/ψπ+π− final state in data, taken from 3 fb−1 of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centre-of-mass pp collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct CP violation, yields a value for the phase ϕs=70±68±8 mrad. This result is consistent with the Standard Model expectation and previous measurements
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