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Abstract: The synthesis of four novel crystalline zeolitic imidazolate framework (ZIF) structures using a mixed-ligand approach is reported. The inclusion of both imidazolate and halogenated benzimidazolate-derived linkers leads to glass-forming behavior by all four structures. Melting temperatures are observed to depend on both electronic and steric effects. Solid-state NMR and terahertz (THz)/Far-IR demonstrate the presence of a Zn-F bond for fluorinated ZIF glasses. In situ THz/Far-IR spectroscopic techniques reveal the dynamic structural properties of crystal, glass and liquid phases of the halogenated ZIFs, linking the melting behavior of ZIFs to the propensity of the ZnN4 tetrahedra to undergo thermally-induced deformation. The inclusion of halogenated ligands within MOF-glasses improves their gas uptake properties.

Open Access

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Abstract: The irreversible loss of lithium from the cathode material during the first cycles of rechargeable Li‐ion batteries notably reduces the overall cell capacity. Here, a new family of sacrificial cathode additives based on Li2O:Li2/3Mn1/3O5/6 composites synthesized by mechanochemical alloying is reported. These nanocomposites display record (but irreversible) capacities within the Li–Mn–O systems studied, of up to 1157 mAh g−1, which represents an increase of over 300% of the originally reported capacity in Li2/3Mn1/3O5/6 disordered rock salts. Such a high irreversible capacity is achieved by the reaction between Li2O and Li2/3Mn1/3O5/6 during the first charge, where electrochemically active Li2O acts as a Li+ donor. A 13% increase of the LiFePO4 and LiCoO2 first charge gravimetric capacities is demonstrated by the addition of only 2 wt% of the nanosized composite in the cathode mixture. This result shows the great potential of these newly discovered sacrificial additives to counteract initial losses of Li+ ions and improve battery performance.

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Abstract: The structural dynamics of a quasi-one-dimensional (1D) mixed-metal cyanide, C u 1 / 3 A g 1 / 3 A u 1 / 3 CN , with intriguing thermal properties is explored. All the current known related compounds with straight-chain structures, such as group 11 cyanides CuCN, AgCN, AuCN, and bimetallic cyanides M x M ′ 1 − x CN ( M , M ′ = Cu , Ag, Au), exhibit 1D negative thermal expansion (NTE) along the chains and positive thermal expansion (PTE) perpendicular to them. C u 1 / 3 A g 1 / 3 A u 1 / 3 CN exhibits similar PTE perpendicular to the chains, however PTE, rather than NTE, is also observed along the chains. In order to understand the origin of this unexpected behavior, inelastic neutron scattering measurements were carried out, underpinned by lattice-dynamical density-functional-theory (DFT) calculations. Synchrotron-based pair-distribution-function analysis and 13 C solid-state nuclear-magnetic-resonance measurements were also performed to build an input structural model for the lattice dynamical study. The results indicate that transverse motions of the metal ions are responsible for the PTE perpendicular to the chains, as is the case for the related group 11 cyanides. However, NTE along the chain due to the tension effect of these transverse motions is not observed. As there are different metal-to-cyanide bond lengths in C u 1 / 3 A g 1 / 3 A u 1 / 3 CN , the metals in neighboring chains cannot all be truly coplanar in a straight-chain model. For this system, DFT-based phonon calculations predict small PTE along the chain due to low-energy chain-slipping modes induced by a bond-rotation effect on the weak metallophilic bonds. However the observed PTE is greater than that predicted with the straight-chain model. Small bends in the chain provide an alternative explanation for thermal behavior. These would mitigate the tension effect induced by the transverse motions of the metals and, as temperature increases and the chains move further apart, a straightening could occur resulting in the observed PTE. This hypothesis is further supported by unusual evolution in the phonon spectra, which suggest small changes in local symmetry with temperature.

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Abstract: We present new results on solid (monolithic) synthetic C-S-H made at room temperature from easily obtainable calcium sources (calcium oxide, calcium hydroxide) and nanosilica (w/s = 2) with a 2 minute mixing time. Using synchrotron X-ray diffraction combined with TGA/DSC, 29Si NMR and synchrotron pair distribution function (PDF) data we show that the solid C-S-H is crystallographically similar to the more conventionally made synthetic C-S-H slurry. We show that C-S-H is present after 1 day curing (C/S = 0.81) and no X-ray visible portlandite is present at day 3. PDF data shows that the ordered domain size is 2.5 – 4.5 nm, depending on the fit chosen.

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Abstract: Protic Ionic Liquids (PIL) prepared from super-strong base 1,7-diazabicyclo[5.4.0]undec-7-ene (DBU) and super-strong acids, trifluoromethane sulfonic acid (TfOH) and (trifluoromethanesulfonyl)-(nonafluorobutylsulfonyl)imide, (IM14H), have been prepared ([DBUH][TfO] and [DBUH][IM14], respectively; the latter for the first time) and their chemical physical properties and structural features been explored using a synergy of experimental and computational tools. The short range order in neat DBU, as well as the long range structural correlations induced by charge correlation and hydrogen bonding interactions in the ionic liquids, have been explored at ambient conditions, where these compounds are proposed for a variety of applications. Similarly to other [DBUH]-based PILs, the probed ones behave as good ionic liquids. Molecular Dynamics-rationalised X-ray diffraction patterns show the major role played by hydrogen bonding in affecting morphology in these systems. Additionally we find further evidence of the existence of fluorous domains in [DBUH][IM14], thus potentially extending the range of applications for these PILs.