Dynamics of Linkers in Metal-Organic Framework Glasses.

Metal-organic framework (MOF) glasses have emerged as a new class of organic-inorganic hybrid glass materials. Considerable efforts have been devoted to unraveling the macroscopic dynamics of MOF glasses by studying their rheological behavior; however, their microscopic dynamics remain unclear. In this work, we studied the effect of vitrification on linker dynamics in ZIF-62 by solid-state 2H nuclear magnetic resonance (NMR) spectroscopy. 2H NMR relaxation analysis provided a detailed picture of the mobility of the ZIF-62 linkers, including local restricted librations and a large-amplitude twist; these details were verified by molecular dynamics. A comparison of ZIF-62 crystals and glasses revealed that vitrification does not drastically affect the fast individual flipping motions with large-amplitude twists, whereas it facilitates slow cooperative large-amplitude twist motions with a decrease in the activation barrier. These observations support the findings of previous studies, indicating that glassy ZIF-62 retains permanent porosity and that short-range disorder exists in the alignment of ligands because of distortion of the coordination angle.

Reduction-Induced Uptake of Cs+ in Metal-Organic Frameworks Loaded with Polyoxometalates.

Materials for Cs+ adsorption continue to be important for the treatment of various solutions. Metal-organic frameworks (MOFs) with large specific surface areas promise adsorption properties for various gases, vapors, and ions. However, the utilization of MOFs for alkali ion capture, specifically, Cs+ capture is still in its infancy. Herein, MOFs are hybridized with polyoxometalates (POMs) to study the effect of i) MOF type, ii) POM type, and iii) POM loading amounts on Cs+ capture. In particular, the composite of ZIF-8 and [α-PMo12O40]3- (PMo12/ZIF-8) adsorbed Cs+ ions effectively when compared to pristine ZIF-8. In addition, the reduction of Mo within the POM from MoVI to MoV by ascorbic acid during the Cs+ uptake process doubled the Cs+ uptake capacity of PMo12/ZIF-8. This observation can be attributed to the increased overall negative charge of the POM facilitating Cs+ uptake to compensate for the charge imbalance. Hybridization with other MOFs (MIL-101 and UiO-66) largely suppresses the Cs+ uptake, highlighting the importance of hydrophobicity in Cs+ capture. Furthermore, PMo12/ZIF-8 led to an outstanding Cs+ uptake (291.5 mg g-1) with high selectivity (79.6%) from quinary mixtures of alkali metal cations even among other representative porous materials (Prussian blue and zeolites).

A redox-active inorganic crown ether based on a polyoxometalate capsule.

Cation-uptake has been long researched as an important topic in materials science. Herein we focus on a molecular crystal composed of a charge-neutral polyoxometalate (POM) capsule [MoVI72FeIII30O252(H2O)102(CH3CO2)15]3+ encapsulating a Keggin-type phosphododecamolybdate anion [α-PMoVI12O40]3-. Cation-coupled electron-transfer reaction occurs by treating the molecular crystal in an aqueous solution containing CsCl and ascorbic acid as a reducing reagent. Specifically, multiple Cs+ ions and electrons are captured in crown-ether-like pores {MoVI3FeIII3O6}, which exist on the surface of the POM capsule, and Mo atoms, respectively. The locations of Cs+ ions and electrons are revealed by single-crystal X-ray diffraction and density functional theory studies. Highly selective Cs+ ion uptake is observed from an aqueous solution containing various alkali metal ions. Cs+ ions can be released from the crown-ether-like pores by the addition of aqueous chlorine as an oxidizing reagent. These results show that the POM capsule functions as an unprecedented "redox-active inorganic crown ether", clearly distinguished from the non-redox-active organic counterpart.

Size-Controlled Synthesis of Luminescent Few-Atom Silver Clusters via Electron Transfer in Isostructural Redox-Active Porous Ionic Crystals.

Ag clusters with a controlled number of atoms have received significant interest because they show size-dependent catalytic, optical, electronic, or magnetic properties. However, the synthesis of size-controlled, ligand-free, and air-stable Ag clusters with high yields has not been well-established. Herein, it is shown that isostructural porous ionic crystals (PICs) with redox-active polyoxometalates (POMs) can be used to synthesize Ag clusters via electron transfer from POMs to Ag+ . Ag clusters with average numbers of three, four, or six atoms emitting blue, green, or red colors, respectively, are formed and stabilized in the PICs under ambient conditions without any protecting ligands. The cluster size solely correlates with the degree of electron transfer, which is controlled by the reduction time and types of ions or elements of the PICs. Thus, advantages have been taken of POMs as electron sources and PICs as scaffolds to demonstrate a convenient method to obtain few-atom Ag clusters.

Vanadium-substituted polycationic Al-oxo cluster in a porous ionic crystal exhibiting Lewis acidity.

Herein we present the first example of a vanadium-substituted δ-Keggin Al13-based (Al28V4) porous Ionic crystal (PIC) (Al28V4-PW9V3). Structural and theoretical studies suggested that Al28V4 may exhibit Lewis acidity, which was confirmed by acetalization reaction with Al28V4-PW9V3 as a solid catalyst and investigations with pyridine or 2,6-lutidine as basic probe molecules. A comparative study with the δ-Keggin Al13 monomer based PIC indicated that the vanadium-substitution gave rise to the Lewis acidity.

Polyoxocationic antimony oxide cluster with acidic protons.

The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H10.7Sb32.1O44][H2.1Sb2.1I8O6][Sb0.76I6]2·25H2O (HSbOI), forming a face-centered cubic structure with cationic Sb32O44 clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb3+ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements.

Basicity of isostructural porous ionic crystals composed of Nb/Ta-substituted Keggin-type polyoxotungstates.

Three isostructural porous ionic crystals (PICs) based on Keggin-type POMs with different compositions but equal negative charge ([BW12O40]5- (BW12), [SiW11NbO40]5- (SiW11Nb), and [SiW11TaO40]5- (SiW11Ta)) are synthesized. Experimental and theoretical characterizations of the three PICs (1_BW12, 1_SiW11Nb, and 1_SiW11Ta) show that the substitution of Nb/Ta for W in the POMs enhances the basicity of PICs, which increases in the order of 1_BW12 < 1_SiW11Nb < 1_SiW11Ta. These findings clearly show that the increase in basicity is due not only to the increase in negative charge of the POM molecule as is often explained, but also to the character of the substituted element itself.

Oxygen Evolution Reaction Driven by Charge Transfer from a Cr Complex to Co-Containing Polyoxometalate in a Porous Ionic Crystal.

Considerable efforts have been devoted to developing oxygen evolution reaction (OER) catalysts based on transition metal oxides. Polyoxometalates (POMs) can be regarded as model compounds of transition metal oxides, and cobalt-containing POMs (Co-POMs) have received significant interest as candidates. Nanocomposites based on Co-POMs have been reported to show high OER activities due to synergistic effects among the components; however, the role of each component is unclear due to its complex structure. Herein, we utilize porous ionic crystals (PICs) based on Co-POMs, which enable a composition-structure-function relationship to be established to understand the origin of the synergistic catalysis. Specifically, a Keggin-type POM [α-CoW12O40]6- and a Cr complex [Cr3O(OOCCH2CN)6(H2O)3]+ are implemented as PIC building blocks for the OER under nonbasic conditions. The potentially OER-active but highly soluble [α-CoW12O40]6- was successfully anchored in the crystalline PIC matrix via Coulomb interactions and hydrogen bonding induced by polar cyano groups of the Cr complex. The PIC exhibits efficient and sustained OER catalytic activity, while each building block is inactive. The Tafel slope of the linear sweep voltammetry curve and the relatively large kinetic isotope effect value suggest that elementary steps closely related to the OER rate involve single-electron and proton transfer reactions. Electrochemical and spectroscopic studies clearly show that the synergistic catalysis originates from the charge transfer from the Cr complex to [α-CoW12O40]6-; the increased electron density of [α-CoW12O40]6- may increase its basicity and accelerate proton abstraction as well as enhance electron transfer to stabilize the reaction intermediates adsorbed on [α-CoW12O40]6-.

Evaluation of the nutrient foramen as a suitable landmark in spinal surgery.

BACKGROUND CONTEXT: The posterior cervical approach is a very popular surgical procedure. Because of the slope-shaped laminae, a suitable landmark for laminectomy, laminoplasty, and pedicle screw placement does not exist. PURPOSE: We investigated the association between the nutrient foramen and spinal canal, and the safety of bone gutter placement using nutrient foramina for safe and effective spinal surgery. STUDY DESIGN: Observational SETTING: University Hospital PATIENT SAMPLES: Two hundred and sixty-six consecutive patients treated for cervical pathologies in our university hospital between January 2005 and December 2019. OUTCOME MEASURES: We identified the location of nutrient foramina and their anatomical association with the spinal canal using preoperative three-dimensional CT scanning. METHODS: We studied the distance between each foramen and the spinal canal, and the angle of the nutrient foramen at each vertebral level. RESULTS: The nutrient foramina were always located outside the spinal canal, with an average distance of +3.06±1.74 mm. The lower the spinal level, the closer the nutrient foramen to the spinal canal. CONCLUSIONS: The nutrient foramen can be considered a reliable landmark when using the posterior cervical approach.

Phase Control of Solid-Solution Nanoparticles beyond the Phase Diagram for Enhanced Catalytic Properties.

The crystal structure, which intrinsically affects the properties of solids, is determined by the constituent elements and composition of solids. Therefore, it cannot be easily controlled beyond the phase diagram because of thermodynamic limitations. Here, we demonstrate the first example of controlling the crystal structures of a solid-solution nanoparticle (NP) entirely without changing its composition and size. We synthesized face-centered cubic (fcc) or hexagonal close-packed (hcp) structured Pd x Ru1-x NPs (x = 0.4, 0.5, and 0.6), although they cannot be synthesized as bulk materials. Crystal-structure control greatly improves the catalytic properties; that is, the hcp-Pd x Ru1-x NPs exceed their fcc counterparts toward the oxygen evolution reaction (OER) in corrosive acid. These NPs only require an overpotential (η) of 200 mV at 10 mA cm-2, can maintain the activity for more than 20 h, greatly outperforming the fcc-Pd0.4Ru0.6 NPs (η = 280 mV, 9 min), and are among the most efficient OER catalysts reported. Synchrotron X-ray-based spectroscopy, atomic-resolution electron microscopy, and density functional theory (DFT) calculations suggest that the enhanced OER performance of hcp-PdRu originates from the high stability against oxidative dissolution.

Incorporating highly basic polyoxometalate anions comprising Nb or Ta into nanoscale reaction fields of porous ionic crystals.

Polyoxometalates (POMs) are oxide cluster anions composed of high-valence early transition metals and are widely used as catalysts. Yet base catalysis of POMs remains an ongoing challenge; group V (V, Nb, and Ta) elements form more negatively charged POMs than group VI (Mo and W) elements, and in particular, polyoxoniobates and polyoxotantalates are known to show strong basicity in solution due to the highly negative surface oxygen atoms. Herein, we report for the first time porous ionic crystals (PICs) comprising Nb or Ta. The PICs are composed of Dawson-type Nb/W or Ta/W mixed-addenda POMs with oxo-centered trinuclear CrIII carboxylates and potassium ions as counter cations to control the crystal structure. Among the PICs, those with Nb or Ta tri-substituted POMs exhibit the highest yield (78-82%) and selectivity (99%) towards the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate (353 K, 6 h), which is a typical base-catalyzed reaction, as reusable solid catalysts, and they can also catalyze the reaction of other active methylene compounds. A detailed investigation into the crystal structures together with DFT calculations and in situ IR spectroscopy with methanol as a basic probe molecule shows that the exposure of [Nb3O13] or [Ta3O13] units with highly negative surface oxygen atoms to the pore surface of PICs is crucial to the catalytic performance. These findings based on the composition-structure-function relationships show that Nb- and Ta-containing PICs can serve as platforms for rational designing of heterogeneous base catalysts.

Isomeric effects on the acidity of Al13 Keggin clusters in porous ionic crystals.

We demonstrate a facile synthesis method of a porous ionic crystal (PIC) composed of the little-known δ-Keggin-type cationic polyoxoaluminum cluster ([δ-Al13O4(OH)24(H2O)12]7+, δ-Al13) with an oppositely-charged polyoxometalate, which enabled us to investigate the activity as a solid acid. The δ-Al13 based PIC exhibited much higher activity in pinacol rearrangement, a typical acid-catalyzed reaction, than the PIC based on the well-known and thermodynamically stable rotational isomer (ε-Al13). This work is a rare example of rotational isomers of polyoxoaluminum clusters exhibiting remarkably different catalytic activities.

Fabrication of Integrated Copper-Based Nanoparticles/Amorphous Metal-Organic Framework by a Facile Spray-Drying Method: Highly Enhanced CO2 Hydrogenation Activity for Methanol Synthesis.

We report on Cu/amUiO-66, a composite made of Cu nanoparticles (NPs) and amorphous [Zr6 O4 (OH)4 (BDC)6 ] (amUiO-66, BDC=1,4-benzenedicarboxylate), and Cu-ZnO/amUiO-66 made of Cu-ZnO nanocomposites and amUiO-66. Both structures were obtained via a spray-drying method and characterized using high-resolution transmission electron microscopy, energy dispersive spectra, powder X-ray diffraction and extended X-ray absorption fine structure. The catalytic activity of Cu/amUiO-66 for CO2 hydrogenation to methanol was 3-fold that of Cu/crystalline UiO-66. Moreover, Cu-ZnO/amUiO-66 enhanced the methanol production rate by 1.5-fold compared with Cu/amUiO-66 and 2.5-fold compared with γ-Al2 O3 -supported Cu-ZnO nanocomposites (Cu-ZnO/γ-Al2 O3 ) as the representative hydrogenation catalyst. The high catalytic performance was investigated using in situ Fourier transform IR spectra. This is a first report of a catalyst comprising metal NPs and an amorphous metal-organic framework in a gas-phase reaction.

Integrating molecular design and crystal engineering approaches in non-humidified intermediate-temperature proton conductors based on a Dawson-type polyoxometalate and poly(ethylene glycol) derivatives.

Anionic metal-oxygen clusters known as polyoxometalates (POMs) have been widely researched as components of proton conductors. While proton conduction under non-humidified intermediate-temperature (100-250 °C) conditions is advantageous from the viewpoint of kinetics, few solid-state materials, not to mention POM-based crystals, show truly effective proton conduction without the aid of water vapor. In this context, non-volatile proton-conductive polymers have been confined into POM-based frameworks, while fast proton conduction was infeasible. Herein, we demonstrate a new strategy to synthesize POM-polymer composites exhibiting fast proton conduction under non-humidified intermediate-temperature conditions. Specifically, a molecular design approach utilizing poly(ethylene glycol)s (PEGs) of different terminal groups or chain lengths controls the proton carrier density, and a crystal engineering approach using a large Dawson-type POM ([α-P2W18O62]6-) with an anisotropic molecular shape and alkali metal ions as counter cations fine-tunes the mobility of the confined PEGs as proton carriers. By integrating these approaches, proton conductivity over 10-4 S cm-1 at 150 °C, comparable to the well-known highly proton-conductive solid-state materials, is achieved. The proton conduction mechanism is discussed with alternative current impedance spectroscopy jointly with specific heat capacity measurements and solid-state NMR spectroscopy.

Ultrahigh Proton Conduction via Extended Hydrogen-Bonding Network in a Preyssler-Type Polyoxometalate-Based Framework Functionalized with a Lanthanide Ion.

The exploration of composition-structure-function relationship in proton-conducting solids remains a challenge in materials chemistry. Polyoxometalate-based compounds have been long considered as candidates for proton conductors; however, their low structural stability and a large decrease in conductivity under reduced relative humidity (RH) have limited their applications. To overcome such limitations, the hybridization of polyoxometalates with proton-conducting polymers has emerged as a promising method. Besides, 4f lanthanide ions possess a high coordination number, which can be utilized to attract water molecules and to build robust frameworks. Herein, a Preyssler-type polyoxometalate functionalized with a 9-coordinate Eu3+ (Eu[P5W30O110K]11-) is newly synthesized and combined with poly(allylamine) with amine moieties as protonation sites. The resulting robust crystalline composite exhibits an ultrahigh proton conductivity >10-2 S cm-1 at 368 K and 90% RH, which is still >10-3 S cm-1 at 50% RH, due to the strengthened and extended hydrogen-bonding network.

Crystalline to amorphous transformation in solid-solution alloy nanoparticles induced by boron doping.

We synthesized a palladium-ruthenium-boron (Pd-Ru-B) solid-solution ternary alloy. Elemental mappings confirmed successful alloying of B with Pd-Ru body without changing the particle sizes, demonstrating the first discovery of this ternary alloy. Pair distribution function analysis revealed a drastic decrease in atomic correlation in Pd-Ru nanoparticles by B doping. This result gives the first example of structural transformation from crystalline to amorphous in solid-solution alloy nanoparticles induced by the doping of light elements.

Isostructural mesoporous ionic crystals as a tunable platform for acid catalysis.

Eleven isostructural mesoporous ionic crystals (meso-PICs) are synthesized. The initial activities of the Barbier-Grignard reaction, which is a typical C-C bond formation reaction, catalyzed by the meso-PICs are dependent on the acid dissociation constant of the aqua ions of Mn+ and the types of polyoxometalates, which construct the meso-PICs.

Probing dynamics of carbon dioxide in a metal-organic framework under high pressure by high-resolution solid-state NMR.

The application of high-resolution NMR analysis for CO2 adsorbed in a MOF under high pressure is reported for the first time. The results showed that CO2 adsorbed in MOF-74 had an unusually slow mobility (τ ∼ 10-8 s). CO2-CO2 interactions suppressed the mobility of CO2 under high pressure, which, in turn, would have contributed to the stability of CO2 at the adsorption sites.

Eosinophilic Cholecystitis Associated with Eosinophilic Granulomatosis with Polyangiitis.

We report a case of eosinophilic cholecystitis associated with eosinophilic granulomatosis with polyangiitis (EGPA) complicated by cerebral hemorrhage. A 60-year-old man presented to a local hospital with a diagnosis of acute cholecystitis, with persistent fever and epigastric pain for 2 weeks. His symptoms persisted despite 3-week hospitalization; therefore, he was transferred to our hospital for further evaluation. Laboratory investigations upon admission showed white blood cells 26,300/µL and significant eosinophilia (eosinophils 61%). Abdominal computed tomography revealed no gallbladder enlargement but a circumferentially edematous gallbladder wall. Additional blood test results were negative for antineutrophil cytoplasmic and perinuclear antineutrophil cytoplasmic antibodies; however, immunoglobulin (Ig)G and IgE levels were high at 1,953 mg/dL and 3,040/IU/mL, respectively. He improved following endoscopic transnasal gallbladder drainage for cholecystitis and was diagnosed with EGPA and received corticosteroid and immunosuppressant combination therapy. The eosinophil count decreased immediately after treatment, and abdominal pain and numbness resolved. He returned with left-sided suboccipital hemorrhage likely attributed to EGPA 6 months after discharge. EGPA is characterized by inflammation of small blood vessels and clinically manifests with an allergic presentation of bronchial asthma, as well as renal dysfunction, interstitial pneumonia, enteritis, and cerebral hemorrhage. Few reports have described cholecystitis as a presenting symptom of EGPA. We report a rare case of such a presentation with added considerations.