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The structural and magnetic properties of a new series of iridium-based honeycomb lattices with the formula Na 3 − δ ( Na 1 − x Mg x ) Ir 2 O 6 ( 0 ≤ x ≤ 1 ) are reported. As x and δ are increased, the honeycomb lattice contracts and the strength of the antiferromagnetic interactions decreases systematically due to a reduction in Ir–O–Ir bond angles. Samples with imperfect stoichiometry exhibit disordered magnetic freezing at temperatures T f between 3.4 K and 5 K. This glassy magnetism likely arises due to the presence of non-magnetic Ir 3+ , which are distributed randomly throughout the lattice, with a possible additional contribution from stacking faults. Together, these results demonstrate that chemical defects and non-stoichiometry have a significant effect on the magnetism of compounds in the A 2 IrO 3 materials family. [ABSTRACT FROM AUTHOR]

Highlights: [•] D2 adsorbed in Ni2(dobdc) exhibits a close metal-D2 distance of 2.20(1)Å. [•] H2 quantum rotational levels determined for 3 adsorption sites. [•] Layering of H2 over D2 reveal the transitions of H2 at the second adsorption site. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure, phonon density-of-states, and magnetic properties of Mn(dca)2(o-phen) (dca=dicyanamide, N(CN)2 −; o-phen=1,10-phenanthroline) have been studied using several methods including magnetization, muon-spin relaxation, and neutron and X-ray scattering. From X-ray crystallography the structure was shown to consist of octahedral MnN6 sites that are connected via four μ1,5-bridging dca ligands while the two remaining cis-positions are occupied by N-donors of the o-phen ligand. Two Mn2+ ions are bridged together by two dca anions to afford [Mn2(dca)2(o-phen)2]2+ “dimers.” These dimers are linked in 2D via μ1,5-dca ligands to afford a polymeric structure whereas the o-phen ligands act as spacers. Bulk magnetic susceptibility data show a characteristic broad maximum at 2.65K while neutron scattering and muon-spin relaxation data establish T N =1.85K. For T ≪ T N, the magnetization, as obtained in pulsed-fields, saturates at 5.75T and reaches a moment typical of an isotropic S =5/2 ion. The magnetic structure was determined and found to consist of antiferromagnetically ordered Mn2+ moments oriented in the ac-plane with no spin-canting being evident. The magnetic space group symmetry for the Mn2+ moments is P21′/c with each Mn2+ ion carrying a magnetic moment of 4.7(1)μB, in good agreement with the value of 5.0μB expected for an isotropic, high-spin S =5/2 ion. The fact that LRO is observed in Mn(dca)2(o-phen) is unusual among low-dimensional dicyanamide complexes especially since only μ1,5-dca modes are involved. [Copyright &y& Elsevier]

Abstract: The catalytic dissociation of hydrogen molecules by metal nanoparticles and spillover of atomic hydrogen onto various supports is a well-established phenomenon in catalysis. However, the mechanisms by which metal catalyst nanoparticles can assist in enhanced hydrogen storage on high-surface area supports are still under debate. Experimental measurements of metal-assisted hydrogen storage have been hampered by inaccurate estimation of atomically stored hydrogen deduced from comparative measurements between metal-decorated and undecorated samples. Here we report a temperature cycling technique combined with inelastic neutron scattering (INS) measurements of quantum rotational transitions of molecular H2 to more accurately quantify adsorbed hydrogen aided by catalytic particles using single samples. Temperature cycling measurements on single-wall carbon nanohorns (SWCNHs) decorated with 2–3nm Pt nanoparticles showed 0.17% mass fraction of metal-assisted hydrogen storage (at ≈0.5MPa) at room temperature. Temperature cycling of Pt-decorated SWCNHs using a Sievert’s apparatus also indicated metal-assisted hydrogen adsorption of ≈0.08% mass fraction at 5MPa at room temperature. No additional metal-assisted hydrogen storage was observed in SWCNH samples without Pt nanoparticles cycled to room temperature. The possible formation of C–H bonds due to spilled-over atomic hydrogen was also investigated using both INS and density functional theory calculations. [Copyright &y& Elsevier]

Abstract: Ordered microporous carbons containing dispersed platinum nanoparticles were fabricated and chosen as suitable models to investigate micro-structure development and hydrogen transport properties of zeolite-templated carbons. X-ray photoelectron spectroscopy analysis revealed that the enhanced heat of adsorption is related to the narrow micro-channels templated from the zeolite and the presence of certain Con the carbon. The lack of a well-defined and intense rotational transition line and the persistent broad H2 recoil spectrum in neutron scattering results suggests a distribution of binding sites. Most interestingly, hydrogen diffusion occurs on two time scales, consisting of a fast liquid-like jump diffusion on the timescale of picoseconds along with an even faster bulk-like diffusion. The liquid-like motion is characterized by a diffusion constant of (2.1±0.3)×10−8 m2/s with an activation energy of ca. 77K; both values indicate somewhat lower mobility than similar dynamics of H2 on nanotubes, activated carbon XC-72, or Grafoil, yet greater mobility than that of bulk liquid. These unusual characteristics for hydrogen in carbons are believed to arise from the network of narrow pores in this zeolite-templated image of the zeolite. In fact, the diffusion constants of the templated carbons are extremely similar to those measured for zeolite 13X. [ABSTRACT FROM AUTHOR]

The time-of-flight method has a long and distinguished history. In one form or another it has been in use at the National Institute of Standards and Technology (NIST), formerly known as the National Bureau of Standards, since 1970. The current incumbent is the Disk Chopper Spectrometer (DCS) [1], a direct geometry machine with an optical filter and cooled graphite filter, seven disk choppers, a sample stage, and 913 non-position-sensitive detectors. Slots of different widths in the pulsing and monochromating choppers enable the user to choose among three distinct intensity/resolution conditions without having to change the wavelength or chopper speeds. In practice the high resolution option is not used because the beam does not have sufficient intensity. On the other hand we have used the narrowest (1.35°) slots in the choppers closest to the sample, with the remaining choppers stopped, for pulsed white beam transmission measurements (e.g. ref. [2]) and for Laue diffraction measurements (to determine the orientations of single crystals of helium grown in situ). [ABSTRACT FROM AUTHOR]

We review recent structural studies that we have undertaken aimed at elucidating the fundamental properties of metal-organic framework materials and their inter- actions with hydrogen. We have shown that exposing coordinatively unsaturated metal centers can greatly enhance the hydrogen binding energy and that they result in a significant increase of the surface packing density of adsorbed hydrogen molecules on materials' surface. We will review some of the structural aspects of these materials, especially the adsorbed hydrogen molecule surface packing density in one type of metal-organic framework, MOF-74, which can be packed even denser than that in solid hydrogen. [ABSTRACT FROM AUTHOR]

Abstract: The hydration of Mg-stabilized triclinic and monoclinic tricalcium silicate samples were studied using quasielastic neutron scattering to follow the fixation of hydrogen into the reaction products and by applying hydration models to the data. The quantity of Ca(OH)2 produced during hydration was also determined using inelastic neutron scattering. The monoclinic form was found to be intrinsically less reactive that the triclinic form. The monoclinic form was also confirmed to produce more product than the triclinic form after 50h, a process found to occur through a longer, rather than earlier, nucleation and growth regime. Results indicated an increase in the permeability of the hydration layer product relative to the triclinic form and the increase in the length of the nucleation and growth regime was thus attributed to an alteration in morphology or structure of the hydration layer product, extending the time for diffusion limited mechanics to be reached. [Copyright &y& Elsevier]

We have used quasielastic neutron scattering to probe the solid-state ligand dynamics in the coordination polymer Mn[N(CN)[SUB2]][SUB2](pyz) {pyz = pyrazine} which has double-interpenetrating 3D lattices. A reversible structural phase transition occurs at 410 K as shown by neutron spectroscopy and differential scanning calorimetry. The origin of this transition is linked to rotational dynamics associated with the bridging pyz ligands. At 425 K, the pyrazine ring motion can be solely regarded as a 180° reorientational jump about the axis defined by the Mn-N coordinative bonds, occurring with a correlation time of ~70 ps. This model can be extended to the 200-410 K temperature region using high-resolution backscattering spectroscopy to measure an identical motion on the time scale of nanoseconds with an activation energy of 24 ± 2 kJ mol[SUP-1]. In contrast, no quasielastic scattering is seen for the 2D layered variant β-Cu[N(CN)[SUB2]][SUB2]-(pyz), owing to its more compact layer packing motif. Importantly, this work represents the very first study of solid-state rotational dynamics in an interpenetrating lattice structure. [ABSTRACT FROM AUTHOR]

The hydrogen storage properties of Mg2(dobdc) (dobdc4−= 2,5-dioxido-1,4-benzenedicarboxylate), a metal–organic framework possessing hexagonal one-dimensional channels decorated with unsaturated Mg2+coordination sites, have been examined through low- and high-pressure adsorption experiments, infrared spectroscopy, and neutron scattering studies. [ABSTRACT FROM AUTHOR]

The structural implications of excess Ni in the TiNiSn half-Heusler compound are examined through a combination of synchrotron x-ray and neutron scattering studies, in conjunction with first principles density functional theory calculations on supercells. Despite the phase diagram suggesting that TiNiSn is a line compound with no solid solution, for small x in TiNi1+xSn there is indeed an appearance--from careful analysis of the scattering--of some solubility, with the excess Ni occupying the interstitial tetrahedral site in the half-Heusler structure. The analysis performed here would point to the excess Ni not being statistically distributed, but rather occurring as coherent nanoclusters. First principles calculations of energetics, carried out using supercells, support a scenario of Ni interstitials clustering, rather than a statistical distribution. [ABSTRACT FROM AUTHOR]

We identify the phase boundary between spiral spin and ferromagnetic phases in Au2 Mn at a critical pressure of 16.4 kbar, as determined by neutron diffraction, magnetization, and magnetoresistance measurements. The temperature-dependent critical field at a given pressure is accompanied by a peak in magnetoresistance and a step in magnetization. The critical field decreases with increasing temperature and pressure. The critical pressure separating the spiral phase and ferromagnetism coincides with the disappearance of the magnetoresistance peak, where the critical field goes to zero. The notable absence of an anomalous Hall effect in the the ferromagnetic phase is attributable to the high conductivity of this material. [ABSTRACT FROM AUTHOR]

Early-age hydration kinetics of Portland cement with nano-additives such as nano-silica (NS) was examined using quasielastic neutron scattering (QENS). Cement pastes with different ratios of Portland cement to NS were prepared. The concentration of the NS played a major role in controlling the free and bound water during the hydration of the cement paste. Additionally, the effects of metakaolin (MK) with NS in Portland cements revealed that MK acts as a retarder by decreasing the bounding water capacity during the early age of hydration. An increase in the concentration of NS affected the degree of hydration by reducing the amount of free and mobile water in the gel pores when compared to Portland cement paste. Here, we show that the concentration of NS governs the early-age hydration process in Portland cements. [ABSTRACT FROM AUTHOR]

Neutron diffraction and spectroscopy offer unique insight into structures and properties of solids and molecular materials. All neutron instruments located at the various neutron sources are distinct, even if their designs are based on similar principles, and thus, they are usually less familiar to the community than commercial X‐ray diffractometers and optical spectrometers. Major neutron instruments in the USA, which are open to scientists around the world, and examples of their use in coordination chemistry research are presented here, along with a list of similar instruments at main neutron facilities in other countries. The reader may easily and quickly find from this minireview an appropriate neutron instrument for research. The instruments include single‐crystal and powder diffractometers to determine structures, inelastic neutron scattering (INS) spectrometers to probe magnetic and vibrational excitations, and quasielastic neutron scattering (QENS) spectrometers to study molecular dynamics such as methyl rotation on ligands. Key and unique features of the diffraction and neutron spectroscopy that are relevant to inorganic chemistry are reviewed. Major instruments in the USA for (1) single‐crystal and powder neutron diffraction and (2) inelastic neutron scattering (INS) and quasielastic neutron scattering (QENS) spectroscopy are presented with examples of their use in coordination chemistry. Similar instruments at main neutron facilities in other countries are listed for the reader to find a suitable neutron instrument for research. [ABSTRACT FROM AUTHOR]

The search for appropriate materials for technological applications is challenging, as real materials are subject to uncontrolled doping and thermal effects. Tetragonal NaMnBi of the I-Mn-V class of antiferromagnetic semiconductors with a Néel transition (TN), above room temperature, can exhibit an extreme magnetoresistance (MR), greater than 10 000% at 2 K and 600% at room temperature and 9 T by quenching disorder into the system. Coupled with the large MR is a re-orientation of the magnetic moment, from a collinear spin arrangement along c to a canted one along the (011) crystallographic axis. The extreme MR is observed in samples with about 15% of Bi vacancies which in turn effectively introduces charge carriers into the lattice, leading to a drastic change in the electronic transport, from semiconducting to metallic, and to the very large MR under the magnetic field. In the absence of Bi defects, the MR is severely suppressed, suggesting that the hybridization of the Mn and Bi orbitals may be key to the field induced large MR. This is the only material of its class that exhibits the extreme MR and may potentially find use in microelectronic devices. [ABSTRACT FROM AUTHOR]

The article presents materials science research study on how Aluminum formate, an earth-abundant material for CO2 capture. Topics include combination of gas adsorption and gas breakthrough measurements show that the metal-organic framework, Al(HCOO)3 (ALF), which can be made inexpensively from commodity chemicals; and preferential adsorption of CO2 is a size-selective separation that depends on the subtle difference between the kinetic diameters of CO2 and nitrogen gas (N2).

Early age hydration kinetics of Portland cement with pozzolanic volcanic ash was examined using quasielastic neutron scattering. Volcanic ash consisting of two different particle sizes was used to prepare cement pastes with different ratios of Portland cement to volcanic ash. The concentration of the volcanic ash played a major role in the bound water index and self-diffusion coefficients of hydration water confined in the cement paste. An increase in the particle size of the volcanic ash affected the degree of hydration by allowing more free and mobile water in the gel pores, suggesting that volcanic ash may not have completely reacted during the experimental time frame. This study shows that the particle size along with variation in volcanic ash composition governs the early age hydration process in volcanic ash cements. [ABSTRACT FROM AUTHOR]

Layered bismuth oxyhalides with bilayered (Bi2O2) fluorite (FL) slabs are promising visible‐light photocatalysts because of their excellent stability and the ability to adjust band levels depending on the layers combined. It is interesting to manipulate the Bi2O2 slab itself, but only trilayered FL blocks (e.g., Bi3O4) are reported so far. Here, a structurally uncharacterized Bi12O17Cl2, which is extensively studied as a photocatalyst for a variety of reactions, has a sextuple Bi6O8.5 block separated by Cl is shown. Unlike double and triple layered cases, the inner region of the Bi6O8.5 block contains 1D rock‐salt (RS) units in the FL matrix along the a‐axis, causing in‐plane corrugation. A topochemical reaction involving anion‐exchange gives Bi12O17–0.5xFxCl2 (x ≤ 6) with alternate FL and RS slabs along the c‐axis. The elimination of the structural corrugation increases higher photo‐conductivity and improves photocatalytic activity against acetic acid decomposition under visible light irradiation. This study paves new opportunities of controlling the properties of layered bismuth oxyhalides by the thickness of Bi–O block, FL/RS configuration, and structural modulation. [ABSTRACT FROM AUTHOR]

MnCl2(urea)2 is a new linear chain coordination polymer that exhibits slightly counter-rotated Mn2Cl2 rhomboids along the chain-axis. The material crystallizes in the noncentrosymmetric orthorhombic space group Iba2, with each Mn(II) ion equatorially surrounded by four Cl- that lead to bibridged ribbons. Urea ligands coordinate via O atoms in the axial positions. Hydrogen bonds of the Cl···H-N and O···H-N type link the chains into a quasi-3D network. Magnetic susceptibility data reveal a broad maximum at 9 K that is consistent with short-range magnetic order. Pulsed-field magnetization measurements conducted at 0.6 K show that a fully polarized magnetic state is achieved at Bsat = 19.6 T with another field-induced phase transition occurring at 2.8 T. Zero-field neutron diffraction studies made on a powdered sample of MnCl2(urea)2 reveal that long-range magnetic order occurs below TN = 3.2(1) K. Additional Bragg peaks due to antiferromagnetic (AFM) ordering can be indexed according to the Ib′a2′ magnetic space group and propagation vector τ = [0, 0, 0]. Rietveld profile analysis of these data revealed a Néel-type collinear ordering of Mn(II) ions with an ordered magnetic moment of 4.06(6) μB (5 μB is expected for isotropic S = 5/2) oriented along the b-axis, i.e., perpendicular to the chain-axis that runs along the c-direction. Owing to the potential for spatial exchange anisotropy and the pitfalls in modeling bulk magnetic data, we analyzed inelastic neutron scattering data to retrieve the exchange constants: Jc = 2.22 K (intrachain), Ja = −0.10 K (interchain), and D = −0.14 K with J > 0 assigned to AFM coupling. This J configuration is most unusual and contrasts the more commonly observed AFM interchain coupling of 1D chains. [ABSTRACT FROM AUTHOR]

Sr2FeMoO6 has been extensively studied for application in spintronic devices. Through the topochemical de-intercalation of oxygen anions with metal hydride reduction, we demonstrate that the high temperature cubic phase is stabilized, at room temperature, whilst leaving the magnetic ordering intact. Synchrotron X-ray and neutron powder diffraction were used to characterize the structure and stoichiometry of the reduced oxide. [ABSTRACT FROM AUTHOR]

The article discusses the importance of high-performing and scalable adsorbent materials in addressing the global demand for energy and mitigating the consequences of burning fossil fuels. Adsorbent materials have porous atomic crystal structures that enable the capture and storage of certain gases at useful temperatures and pressures. The article focuses on a specific material called aluminum formate (ALF), which has shown promise in capturing CO2 and storing hydrogen gas. ALF's simple preparation from commodity chemicals and low cost make it a viable solution for CO2 capture and grid-scale H2 storage. However, ALF's instability in humid conditions and the question of what to do with potentially massive quantities of ALF are challenges that need to be addressed. The article also highlights ALF's ability to separate gases and store appreciable amounts of H2 gas at moderate temperatures and pressures, making it a potential solution for large-scale grid-scale H2 storage. [Extracted from the article]

Abstract: Energy barriers for rotation of –NH3 and –BH3 in the orthorhombic phase of ammonia borane, NH3BH3, were determined using quasielastic neutron scattering (QENS). QENS confirms the 3-site jump model of rotational diffusion and yields barrier heights of 23.6±1.0kJ/mol and 14.8±0.4kJ/mol for the borane and amine groups, respectively, which are comparable to barrier heights determined by recent 2H and 15N NMR studies suggesting no significant isotope effect on rotational motion in the orthorhombic phase of ammonia borane. [Copyright &y& Elsevier]

Layered hybrid organic–inorganic compounds of the transition metal hydroxides, in which part of the hydroxide ions are exchanged for organic ligands that act as spacers of the 2-dimensional inorganic layers, elicit new or enhanced properties. The interlayer ligands enable fine-tuning of the physicochemical properties of the metal hydroxide layers, including their magnetism. Specifically, within the Co(OH) 2 family of transition ion hydroxides, this approach has been leveraged to stabilize antiferromagnetic and ferrimagnetic ground states for pillared and layered complexes, respectively. Here, we further investigate the effects of changing dimensionality, local Co coordination, and interlayer spacing on the magnetic ground state of brucite-like β -Co(OH) layered complexes. We report the hydrothermal synthesis of a new crystalline material, Co(OH)(sorb), where the inorganic layers are spaced by monotopic, doubly unsaturated sorbate ligands (sorb = [C 6 H 7 O 2 ]−). The material was structurally characterized using powder X-ray and neutron diffraction measurements and the crystal structure was solved ab initio from powder diffraction data and refined using the Rietveld method. The magnetic susceptibility and magnetization measurements reveal canted antiferromagnetic ordering with T N = 41.7 K. This report augments our understanding of tuning magnetism through dimensionality in layered complexes and represents a step forward in the design of new 2D layered hybrid compounds. [ABSTRACT FROM AUTHOR]

Close H---H contacts exist in LaNiInH1.6 and in CeNiInH1.4, which leads to softening and splitting of the metal-hydride modes in the spectra compared to the parent LaNiInH0.67 compound. A team of researchers - with members from the NIST Center for Neutron Research (NCNR), Oak Ridge National Laboratory (ORNL), and the Institute for Energy Technology (Kjeller, Norway) - investigated the neutron vibrational spectroscopic signatures of close H---H contacts in the I R i NiInH I SB x sb i metal hydrides [[6]]. By coupling NVS experiments with DFT calculations, the researchers showed the spectral signatures of close H---H contacts in the I R i NiInH I SB x sb i family of metal hydrides. [Extracted from the article]

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan is one other place in the solar system that has large amounts of these compounds. On Titan, organic molecules are produced in the atmosphere and carried to the surface where they can mineralize. Here, we report the phase diagram of mixtures of acetonitrile and benzene, and provide an account of the structure and composition of the phases. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The results provide new insights into the structure and stability of potential extraterrestrial minerals. In light of Dragonfly, NASA's upcoming mission to Titan, revisiting the fundamental chemistry of the smallest molecules with modern methods and techniques can have significant contributions to this epochal mission and can open new research directions in chemistry. [ABSTRACT FROM AUTHOR]

The graphite intercalation compound KC24 adsorbs hydrogen gas at low temperatures up to a maximum stoichiometry of KC24(H2)2, with a differential enthalpy of adsorption of approximately -9 kJ mol-1. The hydrogen molecules and potassium atoms form a two-dimensional condensed phase between the graphite layers. Steric barriers and strong adsorption potentials are expected to strongly hinder hydrogen diffusion within the host KC24 structure. In this study, self-diffusion in a KC24(H2)0.5 sample is measured experimentally by quasielastic neutron scattering and compared to values from molecular dynamics simulations. Self-diffusion coefficients are determined by fits of the experimental spectra to a honeycomb net diffusion model and found to agree well with the simulated values. The experimental H2 diffusion coefficients in KC24 vary from 3.6 × 10-9 m2 s-1 at 80 K to 8.5 × 10-9 m2 s-1 at 110 K. The measured diffusivities are roughly an order of magnitude lower that those observed on carbon adsorbents, but compare well with the rate of hydrogen self-diffusion in molecular sieve zeolites. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks featuring open metal coordination sites have been widely studied for the separation of gas mixtures. For CO2/N2 separations, these materials have shown considerable promise. Herein, we report the characterization of a subset of the well-known PCN-250 class of frameworks upon CO2 adsorption via powder neutron diffraction methods. Noteably, in contrast to previously reported data, they display only moderate CO2 adsorption enthalpies, based on metal cation–CO2 interactions. Further, we show charge balance in these materials is likely achieved via ligand vacancies rather than the presence of μ3-OH groups in the trimetallic cluster that comprises them. [ABSTRACT FROM AUTHOR]

In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deutrated tetrahydrofuran-water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J=0 and 1 states) at approximately 14 meV in both energy gain and loss. These transitions could be unequivocally assigned since there was residual orthohydrogen at low temperatures (slow conversion to the ground state) resulting in an observable J=1→0 transition at 5 K (kT=0.48 meV). A doublet in neutron energy loss at approximately 28.5 meV is interpreted as J=1→2 transitions. In addition to the transitions between rotational states, there are a series of peaks that arise from transitions between center-of-mass translational quantum states of the confined hydrogen molecule. A band at approximately 9 meV can be unequivocally interpreted as a transition between translational states, while broad features at 20, 25, 35, and 50–60 meV are also interpreted to as transitions between translational quantum states. A detailed comparison is made with a recent five-dimensional quantum treatment of hydrogen in the smaller dodecahedral cage in the SII ice-clathrate structure. Although there is broad agreement regarding the features such as the splitting of the J=1 degeneracy, the magnitude of the external potential is overestimated. The numerous transitions between translational states predicted by this model are in poor agreement with the experimental data. Comparisons are also made with three simple exactly solved models, namely, a particle in a box, a particle in a sphere, and a particle on the surface of a sphere. Again, there are too many predicted features by the first two models, but there is reasonable agreement with the particle on a sphere model. This is consistent with published quantum chemistry results for hydrogen in the dodecahedral 512 cage, where the center of the cage is found to be energetically unfavorable, resulting in a shell-like confinement for the hydrogen molecule wave function. These results demonstrate that translational quantum effects are very significant and a classical treatment of the hydrogen molecule dynamics is inappropriate under such conditions. [ABSTRACT FROM AUTHOR]

Herein we present a detailed study of the hydrogen adsorption properties of Cu‐BTTri, a robust crystalline metal–organic framework containing open metal‐coordination sites. Diffraction techniques, carried out on the activated framework, reveal a structure that is different from what was previously reported. Further, combining standard hydrogen adsorption measurements with in‐situ neutron diffraction techniques provides molecular level insight into the hydrogen adsorption process. The diffraction experiments unveil the location of four D2 adsorption sites in Cu‐BTTri and shed light on the structural features that promote hydrogen adsorption in this material. Density functional theory (DFT), used to predict the location and strength of binding sites, corroborate the experimental findings. By decomposing binding energies in different sites in various energetic contributions, we show that van der Waals interactions play a crucial role, suggesting a possible route to enhancing the binding energy around open metal coordination sites. The correct structure of a well‐known metal–organic framework (MOF), Cu‐BTTri, has been defined by means of in‐situ diffraction techniques. The in‐situ neutron diffraction technique, coupled with detailed DFT studies, has led to a deep understanding of the chemical and structural parameters influencing hydrogen adsorption in MOFs. [ABSTRACT FROM AUTHOR]

Co(acac)2(H2O)2 (1, acac = acetylacetonate), a transition metal complex (S = 3/2), displays field‐induced slow magnetic relaxation as a single‐molecule magnet. For 1 and its isotopologues Co(acac)2(D2O)2 (1‐d4) and Co(acac‐d7)2(D2O)2 (1‐d18) in approximately D4h symmetry, zero‐field splitting of the ground electronic state leads to two Kramers doublets (KDs): lower energy MS = ±1/2 (ϕ1,2) and higher energy MS = ±3/2 (ϕ3,4) states. This work employs inelastic neutron scattering (INS), a unique method to probe magnetic transitions, to probe different magnetic excitations in 1‐d4 and 1‐d18. Direct‐geometry, time‐of‐flight Disk‐Chopper Spectrometer (DCS), with applied magnetic fields up to 10 T, has been used to study the intra‐KD transition as a result of Zeeman splitting, MS = –1/2 (ϕ1) → MS = +1/2 (ϕ2), in 1‐d18. This is a rare study of the MS = –1/2 → MS = +1/2 excitation in transition metal complexes by INS. Indirect‐geometry INS spectrometer VISION has been used to probe the inter‐KD, ZFS transition, MS = ±1/2 (ϕ1,2) → MS = ±3/2 (ϕ3,4) in both 1‐d4 and 1‐d18, by variable‐temperature (VT) properties of this excitation. The INS spectra measured on VISION also give phonon features of the complexes that are well described by periodic DFT phonon calculations. Inelastic Neutron Scattering (INS) has been used to probe intra‐ and inter‐Kramers doublet transitions in Co(acac‐d7)2(D2O)2 (1‐d18) using both variable‐magnetic fields and temperatures. These measurements and INS of Co(acac)2(D2O)2 (1‐d4), coupled with periodic DFT phonon calculations, help reveal magnetic and vibrational properties of the single‐molecule magnets (SMMs). [ABSTRACT FROM AUTHOR]

Square‐planar coordinate Ni2+ ions in oxides are exclusively limited to a low‐spin state (S=0) owing to extensive crystal field splitting. Layered oxychalcogenides A2NiIIO2Ag2Se2 (A=Sr, Ba) with the S=1 NiO2 square lattice are now reported. The structural analysis revealed that the Ni2+ ion is under‐bonded by a significant tensile strain from neighboring Ag2Se2 layers, leading to the reduction in crystal field splitting. Ba2NiO2Ag2Se2 exhibits a G‐type spin order at 130 K, indicating fairly strong in‐plane interactions. The high‐pressure synthesis employed here possibly assists the expansion of NiO2 square lattice by taking the advantage of the difference in compressibility in oxide and selenide layers. All in a spin: A high‐pressure reaction allows the synthesis of A2NiO2Ag2Se2 (A=Sr, Ba) with a square‐planar NiO2 sheet. These materials (and Cu/Mn analogues) have extremely long Ni−O (Cu/Mn−O) bonds owing to an extensive strain from AgSe layers, enabling an otherwise missing S=1 square‐planar state. The distinct compressibility between oxide and chalcogenide layers accounts for this phenomenon. [ABSTRACT FROM AUTHOR]

Square‐planar coordinate Ni2+ ions in oxides are exclusively limited to a low‐spin state (S=0) owing to extensive crystal field splitting. Layered oxychalcogenides A2NiIIO2Ag2Se2 (A=Sr, Ba) with the S=1 NiO2 square lattice are now reported. The structural analysis revealed that the Ni2+ ion is under‐bonded by a significant tensile strain from neighboring Ag2Se2 layers, leading to the reduction in crystal field splitting. Ba2NiO2Ag2Se2 exhibits a G‐type spin order at 130 K, indicating fairly strong in‐plane interactions. The high‐pressure synthesis employed here possibly assists the expansion of NiO2 square lattice by taking the advantage of the difference in compressibility in oxide and selenide layers. [ABSTRACT FROM AUTHOR]

Structurally related to the iron-based superconductors, two new intercalated iron chalcogenides (H0.5NH3)Fe2Ch2 where Ch = S, Se have been prepared. By topochemical conversion, the protons were exchanged by lithium to form (Li0.5NH3)Fe2Ch2. Hydrogen bonding plays a significant role in the guest–host interactions of these intercalated phases. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of two novel pillared coordination cages is reported. By utilizing 1,4-diazabicyclo[2.2.2]octane (dabco) as a pillar with increased basicity as compared to pyrazine or 4,4′-bipyridine, a stable copper-based material was prepared. Extending this strategy to iron(ii) afforded an isostructural material that similarly retains high porosity and crystallinity upon solvent evacuation. Importantly, the iron solid represents a rare example of porous iron paddlewheel-based metal–organic material that is stable to solvent evacuation. Neutron powder diffraction studies on these materials indicate the triangular and square windows of the cage are prime ethane and ethylene adsorption sites. [ABSTRACT FROM AUTHOR]

Recent reports on high capacities delivered by Li-excess transition-metal oxide cathodes have triggered intense interest in utilizing reversible oxygen redox for high-energy battery applications. To control oxygen electrochemical activities, fundamental understanding of redox chemistry is essential yet has so far proven challenging. In the present study, micrometer-sized Li1.3Nb0.3Mn0.4O2 single crystals were synthesized for the first time and used as a platform to understand the charge compensation mechanism during Li extraction and insertion. We explicitly demonstrate that the oxidation of O2- to On- (0 < n < 2) and O2 loss from the lattice dominates at 4.5 and 4.7 V, respectively. While both processes occur in the first cycle, only the redox of O2-/On- participates in the following cycles. The lattice anion redox process triggers irreversible changes in Mn redox, which likely causes the voltage and capacity fade observed on this oxide. Two drastically different redox activity regions, a single-phase behavior involving only Mn3+/4+ and a two-phase behavior involving O2-/On- (0 ≤ n < 2), were found in LixNb0.3Mn0.4O2 (0 < x < 1.3). Morphological damage with particle cracking and fracturing was broadly observed when O redox is active, revealing additional challenges in utilizing O redox for high-energy cathode development. [ABSTRACT FROM AUTHOR]

A growing number of transition metal oxyhydrides have recently been reported, but they are all confined to perovskite-related structures with corner-shared octahedra. Using high pressure synthesis, we have obtained vanadium oxyhydrides BaVO3-xHx (0.3 ≤ x ≤ 0.8) with a 6H-type hexagonal layer structure consisting of face-shared as well as corner-shared octahedra. Synchrotron X-ray and neutron diffraction measurements revealed that, in BaVO2.7H0.3, H- anions are located selectively at the face-shared sites, as supported by DFT calculations, while BaVO2.2H0.8 contains H- anions at both sites though the face-shared preference is partially retained. The selective hydride occupation for BaVO2.7H0.3 appears to suppress electron hopping along the c axis, making this material a quasi-two-dimensional metal characterized by anomalous temperature dependence of the electrical resistivity and strong antiferromagnetic fluctuations. In contrast, the anion disordered BaVO3-xHx in hexagonal (x ≈ 0.8) and cubic (x ≈ 0.9) forms exhibits a semiconducting behavior. This study offers a wide opportunity to develop transition metal oxyhydrides having various polyhedral linkages, along with site preference of H/O anions, aimed at finding interesting phenomena. [ABSTRACT FROM AUTHOR]

Purification of the C8 alkylaromatics o-xylene, mxylene, p-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal-organic frameworks Co2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) and Co2(m-dobdc) (mdobdc4- = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co2(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co2(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C8 guest molecule with two adjacent cobalt(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M2(dobdc) structure, Co2(dobdc) exhibits an unexpected structural distortion in the presence of either o-xylene or ethylbenzene that enables the accommodation of additional guest molecules. [ABSTRACT FROM AUTHOR]

Long carrier lifetime is what makes hybrid organic-inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance. [ABSTRACT FROM AUTHOR]

Small-molecule binding in metal-organic frameworks (MOFs) can be accurately studied both experimentally and computationally, provided the proper tools are employed. Herein, we compare and contrast properties associated with guest binding by means of density functional theory (DFT) calculations using nine different functionals for the M2(dobdc) (dobdc4- = 2,5-dioxido,1,4-benzenedicarboxylate) series, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. Additionally, we perform Quantum Monte Carlo (QMC) calculations for one system to determine if this method can be used to assess the performance of DFT. We also make comparisons with previously published experimental results for carbon dioxide and water and present new methane neutron powder diffraction (NPD) data for further comparison. All of the functionals are able to predict the experimental variation in the binding energy from one metal to the next; however, the interpretation of the performance of the functionals depends on which value is taken as the reference. On the one hand, if we compare against experimental values, we would conclude that the optB86b-vdW and optB88-vdW functionals systematically overestimate the binding strength, while the second generation of van der Waals (vdW) nonlocal functionals (vdw-DF2 and rev-vdW-DF2) correct for this providing a good description of binding energies. On the other hand, if the QMC calculation is taken as the reference then all of the nonlocal functionals yield results that fall just outside the error of the higher-level calculation. The empirically corrected vdW functionals are in reasonable agreement with experimental heat of adsorptions but under bind when compared with QMC, while Perdew-Burke-Ernzerhof fails by more than 20 kJ/mol regardless of which reference is employed. All of the functionals, with the exception of vdW-DF2, predict reasonable framework and guest binding geometries when compared with NPD measurements. The newest of the functionals considered, rev-vdW-DF2, should be used in place of vdW-DF2, as it yields improved bond distances with similar quality binding energies. [ABSTRACT FROM AUTHOR]

Extreme toxicity, corrosiveness, and volatility pose serious challenges for the safe storage and transportation of elemental chlorine and bromine, which play critical roles in the chemical industry. Solid materials capable of forming stable nonvolatile compounds upon reaction with elemental halogens may partially mitigate these challenges by allowing safe halogen release on demand. Here we demonstrate that elemental halogens quantitatively oxidize coordinatively unsaturated Co(II) ions in a robust azolate metal-organic framework (MOF) to produce stable and safe-to-handle Co(III) materials featuring terminal Co(III)-halogen bonds. Thermal treatment of the oxidized MOF causes homolytic cleavage of the Co(III)-halogen bonds, reduction to Co(II), and concomitant release of elemental halogens. The reversible chemical storage and thermal release of elemental halogens occur with no significant losses of structural integrity, as the parent cobaltous MOF retains its crystallinity and porosity even after three oxidation/reduction cycles. These results highlight a material operating via redox mechanism that may find utility in the storage and capture of other noxious and corrosive gases. [ABSTRACT FROM AUTHOR]

We present a general strategy to synthesize metastable layered materials via topochemical deintercalation of thermodynamically stable phases. Through kinetic control of the deintercalation reaction, we have prepared two hypothesized metastable compounds, CoSe and CoS, with the anti-PbO type structure from the starting compounds KCo2Se2 and KCo2S2, respectively. Thermal stability, crystal structure from X-ray and neutron diffraction, magnetic susceptibility, magnetization, and electrical resistivity are studied for these new layered chalcogenides; both CoSe and CoS are found to be weak itinerant ferromagnets with Curie temperatures close to 10 K. Due to the weak van der Waals forces between the layers, CoSe is found to be a suitable host for further intercalation of guest species such as Li-ethylenediamine. From first-principles calculations, we explain why the Co chalcogenides are ferromagnets instead of superconductors as in their iron analogues. Bonding analysis of the calculated electronic density of states both explains their phase stability and predicts the limits of our deintercalation technique. Our results have broad implications for the rational design of new two-dimensional building blocks for functional materials. [ABSTRACT FROM AUTHOR]

By using a high-pressure reaction, we prepared a new oxynitride ZnTaO2N that crystallizes in a centrosymmetric (R3̅c) high-temperature LiNbO3-type structure (HTLN-type). The stabilization of the HTLN-type structure down to low temperatures (at least 20 K) makes it possible to investigate not only the stability of this phase, but also the phase transition to a noncentrosymmetric (R3c) LiNbO3-type structure (LN-type) which is yet to be clarified. Synchrotron and neutron diffraction studies in combination with transmission electron microscopy show that Zn is located at a disordered 12c site instead of 6a, implying an order-disorder mechanism of the phase transition. It is found that the closed d-shell of Zn2+, as well as the high-valent Ta5+ ion, is responsible for the stabilization of the HTLN-type structure, affording a novel quasitriangular ZnO2N coordination. Interestingly, only 3% Zn substitution for MnTaO2N induces a phase transition from LN- to HTLN-type structure, implying the proximity in energy between the two structural types, which is supported by the first-principles calculations. [ABSTRACT FROM AUTHOR]

Two ordered phases of the novel solid superionic conductor sodium 1-carba- closo -decaborate (NaCB 9 H 10 ) were identified via synchrotron x-ray powder diffraction in combination with first-principles calculations and neutron vibrational spectroscopy. A monoclinic packing of the large ellipsoidal CB 9 H 10 − anions prevails at the lowest temperatures, but a first-order transformation to a slightly modified orthorhombic packing is largely complete by 240 K. The CB 9 H 10 − anion orientational alignments and Na + cation interstitial sitings in both phases are arranged so as to minimize the cation proximities to the uniquely more positive C-bonded H atoms of the anions. These results provide valuable structural information pertinent to understanding the relatively low-temperature, entropy-driven, order-disorder phase transition for this compound. [ABSTRACT FROM AUTHOR]

The high-pressure synthesis of a manganese oxyhydride LaSrMnO3.3H0.7 is reported. Neutron and X-ray Rietveld analyses showed that this compound adopts the K2NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen-deficient phases down to LaSrMnO3.5. This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition-metal oxyhydrides. Magnetic susceptibility revealed a spin-glass transition at 24 K that is due to competing ferromagnetic (Mn2+-Mn3+) and antiferromagnetic (Mn2+-Mn2, Mn3+-Mn3+) interactions. [ABSTRACT FROM AUTHOR]

The high-pressure synthesis of a manganese oxyhydride LaSrMnO3.3H0.7 is reported. Neutron and X-ray Rietveld analyses showed that this compound adopts the K2NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen-deficient phases down to LaSrMnO3.5. This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition-metal oxyhydrides. Magnetic susceptibility revealed a spin-glass transition at 24 K that is due to competing ferromagnetic (Mn2+-Mn3+) and antiferromagnetic (Mn2+-Mn2, Mn3+-Mn3+) interactions. [ABSTRACT FROM AUTHOR]

A chromium(II)-based metal-organic framework Cr3[(Cr4Cl)3(BTT)8]2 (Cr-BTT; BTT3−=1,3,5-benzenetristetrazolate), featuring coordinatively unsaturated, redox-active Cr2+ cation sites, was synthesized and investigated for potential applications in H2 storage and O2 production. Low-pressure H2 adsorption and neutron powder diffraction experiments reveal moderately strong Cr-H2 interactions, in line with results from previously reported M-BTT frameworks. Notably, gas adsorption measurements also reveal excellent O2/N2 selectivity with substantial O2 reversibility at room temperature, based on selective electron transfer to form CrIII superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O2 binding. [ABSTRACT FROM AUTHOR]