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Abstract: The metal–organic framework (Me2NH2)2[Cd(NO2BDC)2] (SHF-81) comprises flattened tetrahedral Cd(O2CR)42− nodes, in which Cd(II) centres are linked via NO2BDC2− ligands (2-nitrobenzene-1,4-dicarboxylate) to give a doubly interpenetrated anionic network, with charge balanced by two Me2NH2+ cations per Cd centre resident in the pores. The study establishes that this is a twinned α-quartz-type structure (trigonal, space group P3x21, x = 1 or 2), although very close to the higher symmetry β-quartz arrangement (hexagonal, P6x22, x = 2 or 4) in its as-synthesised solvated form [Cd(NO2BDC)2]·2DMF·0.5H2O (SHF-81-DMF). The activated MOF exhibits very little N2 uptake at 77 K, but shows significant CO2 uptake at 273–298 K with an isosteric enthalpy of adsorption (ΔHads) at zero coverage of −27.4 kJ mol−1 determined for the MOF directly activated from SHF-81-DMF. A series of in situ diffraction experiments, both single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD), reveal that the MOF is flexible and exhibits breathing behaviour with observed changes as large as 12% in the a- and b-axes (|Δa|, |Δb| < 1.8 Å) and 5.5% in the c-axis (|Δc| < 0.7 Å). Both the solvated SHF-81-DMF and activated/desolvated SHF-81 forms of the MOF exhibit linear negative thermal expansion (NTE), in which pores that run parallel to the c-axis expand in diameter (a- and b-axis) while contracting in length (c-axis) upon increasing temperature. Adsorption of CO2 gas at 298 K also results in linear negative expansion (Δa, Δb > 0; Δc < 0; ΔV > 0). The largest change in dimensions is observed during activation/desolvation from SHF-81-DMF to SHF-81 (Δa, Δb < 0; Δc > 0; ΔV < 0). Collectively the nine in situ diffraction experiments conducted suggest the breathing behaviour is continuous, although individual desolvation and adsorption experiments do not rule out the possibility of a gating or step at intermediate geometries that is coupled with continuous dynamic behaviour towards the extremities of the breathing amplitude.

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Abstract: Renewable technologies, and in particular the electric vehicle revolution, have generated tremendous pressure for the improvement of lithium ion battery performance. To meet the increasingly high market demand, challenges include improving the energy density, extending cycle life and enhancing safety. In order to address these issues, a deep understanding of both the physical and chemical changes of battery materials under working conditions is crucial for linking degradation processes to their origins in material properties and their electrochemical signatures. In situ and operando synchrotron-based X-ray techniques provide powerful tools for battery materials research, allowing a deep understanding of structural evolution, redox processes and transport properties during cycling. In this review, in situ synchrotron-based X-ray diffraction methods are discussed in detail with an emphasis on recent advancements in improving the spatial and temporal resolution. The experimental approaches reviewed here include cell designs and materials, as well as beamline experimental setup details. Finally, future challenges and opportunities for battery technologies are discussed.

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Abstract: In this study we show how non-trivial equilibrium and kinetic adsorption behaviour in a flexible zeolite can be understood through a combination of experimental characterisation and modelling. Flexible zeolites, such as those in the RHO-family, can exhibit unusual stepped isotherms in the presence of CO2, but their structural complexity makes it hard to attribute a clear mechanism. Here we present a structural and kinetic study on (Na,TEA)-ZSM-25, an extended member of the RHO-family, and show that by combining diffraction data, lattice fluid modelling and dynamic column experiments, we obtain a plausible mechanism for CO2 adsorption and transport in this material. It is evident that by using any single technique, the behaviour is too complex to be readily understood. This is to our knowledge the first study to measure and model the changing kinetics due to adsorption induced framework flexibility.

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Abstract: Designing porous materials which can selectively adsorb CO2 or CH4 is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO2 and CH4 using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO2 and CH4 in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO2 molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO2. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.

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Abstract: Solid solutions between the known compounds Ca2FeO3CuCh and Sr2FeO3CuCh (Ch = S, Se) in which there are two fairly similar sites (8 and 9 coordinate) for the alkaline earth cations are not attainable under standard high temperature solid state syntheses under thermodynamic control. Instead compounds with greater condensation of FeO5 square pyramids form as these afford one 8-coordinate site and one 12-coordinate site for the alkaline earths which is better suited to the size-mismatched cations in the compounds Sr3-xCaxFe2O5Cu2Ch2 (Ch = S, Se; x = 1, 2). Sr2CaFe2O5Cu2S2, SrCa2Fe2O5Cu2S2, Sr2CaFe2O5Cu2Se2 and SrCa2Fe2O5Cu2Se2 all crystallise in the tetragonal space group I4/mmm with two formula units in the unit cell with the crystal structure first described for Sr3Fe2O5Cu2S2. Oxide slabs composed of vertex-sharing FeO5 square pyramids are separated by Cu2Ch2 anti-fluorite-type layers. The larger Sr2+ ions have a strong preference for the 12-coordinate site in the oxide slabs, while Ca2+ cations dominate the 8-coordinate sites separating the oxide and chalcogenide slabs. Powder neutron diffraction reveals that all the compounds display antiferromagnetic long range ordering of the Fe3+ moments with ordering temperatures well above room temperature and exceeding 526 K in the case of Ca2SrFe2O5Cu2Se2.