Improving the mechanical stability of zirconium-based metal-organic frameworks by incorporation of acidic modulators

Acidic modulating ligands have been shown to stabilize UiO metal-organic frameworks against structural collapse under ball-milling.T.D.B. would like to thank Trinity Hall for funding, along with Professor Anthony K. Cheetham for use of lab facilities. D.D.V. is grateful to IWT (MOF Shape), KU Leuven for support in the Metusalem grant CASAS and IAP 7/05 Functional Supramolecular Systems. I.S. and B.B. thank Research Foundation – Flanders (FWO) for Ph.D. fellowships.This is the accepted manuscript. The final published version is available from RSC at http://pubs.rsc.org/en/Content/ArticleLanding/2015/TA/c4ta06396a#!divAbstract

Connecting defects and amorphization in UiO-66 and MIL-140 metal-organic frameworks: a combined experimental and computational study.

The mechanism and products of the structural collapse of the metal-organic frameworks (MOFs) , and upon ball-milling are investigated through solid state (13)C NMR and pair distribution function (PDF) studies, finding amorphization to proceed by the breaking of a fraction of metal-ligand bonding in each case. The amorphous products contain inorganic-organic bonding motifs reminiscent of the crystalline phases. Whilst the inorganic Zr6O4(OH)4 clusters of remain intact upon structural collapse, the ZrO backbone of the frameworks undergoes substantial distortion. Density functional theory calculations have been performed to investigate defective models of and show, through comparison of calculated and experimental (13)C NMR spectra, that amorphization and defects in the materials are linked.The manuscript was written through contributions of all authors. TDB conceived the initial project. T.D.B. acknowledges Trinity Hall (University of Cambridge) and Professor Anthony K. Cheetham for use of lab facilities. D.G.R. acknowledges the UK MRC for financial support. The authors acknowledge Diamond Light Source for the provision of synchrotron access to Beamline I15 (ex p. EE9691) and Philip A. Chater and Andrew Cairns for assistance with data collection. T.K.T. and C.M.D. thank the French National Research Agency (ANR project: HOPFAME ANR-13-BS07-0002-01) and the Foundation de l'Orangerie for funding. The calculations have been performed using the HPC resources from GENCI (CINES/TGCC/IDRIS) through Grant (2015-097343 and -091461). B.B., B.V.d.V. and D.D.V . gratefully acknowledge the FWO for funding (aspirant grant).This is the final version of the article. It was first available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5CP06798

Towards metal-organic framework based field effect chemical sensors: UiO-66-NH2 for nerve agent detection

We present a highly sensitive gas detection approach for the infamous 'nerve agent' group of alkyl phosphonate compounds. Signal transduction is achieved by monitoring the work function shift of metal-organic framework UiO-66-NH2 coated electrodes upon exposure to ppb-level concentrations of a target simulant. Using the Kelvin probe technique, we demonstrate the potential of electrically insulating MOFs for integration in field effect devices such as ChemFETs: a three orders of magnitude improvement over previous work function-based detection of nerve agent simulants. Moreover, the signal is fully reversible both in dry and humid conditions, down to low ppb concentrations. Comprehensive investigation of the interactions that lead towards this high sensitivity points towards a series of confined interactions between the analyte and the pore interior of UiO-66-NH2

Curvature homogeneous spacelike Jordan Osserman pseudo-Riemannian manifolds

Let s be at least 2. We construct Ricci flat pseudo-Riemannian manifolds of signature (2s,s) which are not locally homogeneous but whose curvature tensors never the less exhibit a number of important symmetry properties. They are curvature homogeneous; their curvature tensor is modeled on that of a local symmetric space. They are spacelike Jordan Osserman with a Jacobi operator which is nilpotent of order 3; they are not timelike Jordan Osserman. They are k-spacelike higher order Jordan Osserman for $2\le k\le s$; they are k-timelike higher order Jordan Osserman for $s+2\le k\le 2s$, and they are not k timelike higher order Jordan Osserman for $2\le s\le s+1$.Comment: Update bibliography, fix minor misprint

Connecting defects and amorphization in UiO-66 and MIL-140 metal–organic frameworks: a combined experimental and computational study

The mechanism and products of the structural collapse of the metal–organic frameworks (MOFs) UiO-66, MIL-140B and MIL-140C upon ball-milling are investigated through solid state 13C NMR and pair distribution function (PDF) studies, finding amorphization to proceed by the breaking of a fraction of metal–ligand bonding in each case. The amorphous products contain inorganic–organic bonding motifs reminiscent of the crystalline phases. Whilst the inorganic Zr6O4(OH)4 clusters of UiO-66 remain intact upon structural collapse, the ZrO backbone of the MIL-140 frameworks undergoes substantial distortion. Density functional theory calculations have been performed to investigate defective models of MIL-140B and show, through comparison of calculated and experimental 13C NMR spectra, that amorphization and defects in the materials are linked.status: publishe

Synthesis modulation as a tool to increase the catalytic activity of metal-organic frameworks: the unique case of UiO-66(Zr)

The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions