X-ray and neutron scattering

Abstract:

and catalytic Lys258 Nζ amino groups an equally shared deuterium is observed in an apparent low-barrier hydrogen bond (LBHB). Density functional theory calculations were performed to provide further evidence of this LBHB interaction. The structural arrangement and the juxtaposition of PMP and Lys258, facilitated by the LBHB, suggests active site preorganization for the incoming ketoacid substrate that initiates the second half-reaction.

Abstract:

We present the results of muon spin relaxation (μSR) and neutron scattering on the Ce-based quasikagome lattice CeRh1-xPdxSn (x=0.1 to 0.75). Our zero-field (ZF) μSR results reveal the absence of both static long-range magnetic order and spin freezing down to 0.05 K in the single-crystal sample of x=0.1. The weak temperature-dependent plateaus of the dynamic spin fluctuations below 0.2 K in ZF-μSR together with its longitudinal-field (LF) dependence between 0 and 3 kG indicate the presence of dynamic spin fluctuations persisting even at T=0.05K without static magnetic order. On the other hand, the magnetic specific heat divided by temperature C4f/T increases as -logT on cooling below 0.9 K, passes through a broad maximum at 0.13 K, and slightly decreases on further cooling. The ac susceptibility also exhibits a frequency-independent broad peak at 0.16 K, which is prominent with an applied field H along the c direction. We, therefore, argue that such a behavior for x=0.1 [namely, a plateau in spin relaxation rate (λ) below 0.2 K and a linear T dependence in C4f below 0.13 K] can be attributed to a metallic spin-liquid-like ground state near the quantum critical point in the frustrated Kondo lattice. The LF-μSR study suggests that the out of kagome plane spin fluctuations are responsible for the spin-liquid (SL) behavior. Low-energy inelastic neutron scattering (INS) of x=0.1 reveals gapless magnetic excitations, which are also supported by the behavior of C4f proportional to T1.1 down to 0.06 K. Our high-energy INS study shows very weak and broad scattering in x=0 and 0.1, which transforms into well-localized crystal-field excitations with increasing x. The ZF-μSR results for the x=0.2 polycrystalline sample exhibit similar behavior to that of x=0.1. A saturation of λ below 0.2 K suggests a spin-fluctuating SL ground state down to 0.05 K. The ZF-μSR results for the x=0.5 sample are interpreted as a long-range antiferromagnetic (AFM) ground state below TN=0.8K, in which the AFM interaction of the enlarged moments probably overcomes the frustration effect. The long-range AFM ordering is also supported by the evolution of magnetic Bragg peaks in x=0.75 sample observed below 5 K in the neutron diffraction data.

Abstract:

Here, we propose the combination of glassy or crystalline metal-organic frameworks (MOFs) with inorganic glasses to create novel hybrid composites and blends.The motivation behind this new composite approach is to improve the processability issues and mechanical performance of MOFs, whilst maintaining their ubiquitous properties. Herein, the precepts of successful composite formation and pairing of MOF and glass MOFs with inorganic glasses are presented. Focus is also given to the synthetic routes to such materials and the challenges anticipated in both their production and characterisation. Depending on their chemical nature, materials are classified as crystalline MOF-glass composites and blends. Additionally, the potential properties and applications of these two classes of materials are considered, the key aim being the retention of beneficial properties of both components, whilst circumventing their respective drawbacks.

Abstract:

Abstract The orientational disorder in crystalline sulfur hexafluoride, SF6, has been studied using a combination of neutron total scattering and the reverse Monte Carlo method. Analysis of the atomic configurations has shown the extent of the disorder through the evaluation of the S–F bond orientational distribution function, consistent with, but improving upon, the results of earlier neutron powder diffraction data. The correlations between orientations of neighbouring molecules have been studied through analysis of the distributions of F–F distances, showing that nearest-neighbour F–F close contacts are avoided, consistent with previous molecular dynamics simulation results. The results present a new case study of the application of neutron total scattering and the reverse Monte Carlo methods for the study of orientational disorder, where in this instance the disorder arises from orientational frustration rather than from a mismatch of molecular and site symmetries.