Observation of a liquid-gas-type transition in the pyrochlore spin ice compound Dy2Ti2O7 in a magnetic field

Low temperature magnetization measurements on the pyrochlore spin ice compound Dy2Ti2O7 reveal that the ice-rule breaking spin flip, appearing at H approximately 0.9 T applied parallel to the [111] direction, turns into a novel first-order transition for T<0.36 K which is most probably of a liquid-gas type. T-linear variation of the critical field observed down to 0.03 K suggests the unusual situation that the entropy release across the transition remains finite [approximately 0.5 (J/K) x mol-Dy] as T-->0, in accordance with a breaking of the macroscopic degeneracy in the intermediate "kagomé ice" state.     

Submillimeter-wave ESR measurements of Ca1−xCuO2 (x = 0.164) with edge-sharing CuO2 chains

Quasi-one-dimensional (1-D) cupric oxide Ca_1?xCuO₂ (x = 0.164) is the system with 25–40% hole-doped edge-sharing CuO₂ chains. However, the holes are almost localized in Ca_1?xCuO₂ and its magnetic susceptibility with a peak at 30 K was explained by the model considering both 1-D antiferromagnetic chains and spin dimers (Z. Hiroi, M. Okumura, Y. Nabeshima, T. Yamada, M. Takano: J. Phys. Soc. Jpn.69, 1824, 2000). To clarify the magnetic nature of Ca_1?xCuO₂, we performed submillimeter-wave electron spin resonance (ESR) measurements on a powder sample of Ca_0.83?6CuO₂. The resonance above 12 K showed typical powder ESR of Cu²⁺ and theg-values were determined to be g∥= 2.33 and g_⊥ = 2.06 from the analysis. The resonance below 12 K changed completely from ESR. The frequency-field relation of ESR at 1.8 K clearly showed the easy-axis type antiferromagnetic resonance.     

Dehydrative glycosylation of tri-O-benzylated 1-hydroxyribofuranose catalyzed by a copper(II) complex

A phosphine/Cu(II) complex catalyzes the dehydrative glycosylation of tri-O-benzylated 1-hydroxyribofuranose to give the ribofuranoside with high stereoselectivity.     

Nickel-catalysed bis-allylation of internal alkynes with triallylindium

The Ni-catalysed reaction of triallylindium with internal alkynes underwent bis-allylation to afford octa-1,4,7-trienes in high yield.     

On the electronic structure and hydrogen evolution reaction activity of platinum group metal-based high-entropy-alloy nanoparticles

We report the synthesis of high-entropy-alloy (HEA) nanoparticles (NPs) consisting of five platinum group metals (Ru, Rh, Pd, Ir and Pt) through a facile one-pot polyol process. We investigated the electronic structure of HEA NPs using hard X-ray photoelectron spectroscopy, which is the first direct observation of the electronic structure of HEA NPs. Significantly, the HEA NPs possessed a broad valence band spectrum without any obvious peaks. This implies that the HEA NPs have random atomic configurations leading to a variety of local electronic structures. We examined the hydrogen evolution reaction (HER) and observed a remarkably high HER activity on HEA NPs. At an overpotential of 25 mV, the turnover frequencies of HEA NPs were 9.5 and 7.8 times higher than those of a commercial Pt catalyst in 0.05 M H₂SO₄ and 1.0 M KOH electrolytes, respectively. Moreover, the HEA NPs showed almost no loss during a cycling test and were much more stable than the commercial Pt catalyst. Our findings on HEA NPs may provide a new paradigm for the design of catalysts.

RuRhPdIrPt high-entropy-alloy nanoparticles with a broad and featureless valence band spectrum show high hydrogen evolution reaction activity.     

A practical procedure for the synthesis of esonarimod, (R,S)-2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid,an antirheumatic agent (part 1)

An efficient and practical procedure for the synthesis of esonarimod, (R,S)-2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (1), a new antirheumatic drug, has been developed. The intermediate, 2-methylene-4-(4-methylphenyl)-4-oxobutanoic acid (2), was prepared by Friedel-Crafts acylation of toluene with itaconic anhydride (3) in the presence of aluminum trichloride and nitrobenzene in 63% yield without silica gel column purification. Compound 1 was prepared by Michael addition of 2 with thioacetic acid (4) in 74% yield. Overall, 1 was obtained in 47% yield from 3. The structures and synthetic mechanisms of by-products (five compounds) of 2 were also clarified.     

Neutron Diffraction Study on the Structure of Aqueous LiNO3 Solutions

Neutron diffraction measurements were carried out at 25 °C for aqueous LiNO₃ heavy water solutions, (*LiNO₃) _x (D₂O)_1?x where x = 0.1, 0.05 and 0.01, in which the ⁶Li/⁷Li isotopic ratios were varied. Structural information on intermolecular nearest neighbor Li⁺···D₂O interactions in the extensive concentration range was derived from the first-order difference function, ?_Li(Q), obtained from the difference in scattering cross sections between ⁶Li- and ⁷Li-enriched sample solutions. The nearest neighbor Li⁺···O distance and coordination number for sample solution with x = 0.1 were determined to be r _LiO = 1.969 (8) Å and n _LiO = 4.12 (6), respectively, corresponding to the four-coordinated Li⁺ ion in the solution. On the other hand, those obtained for the solution with x = 0.01 are r _LiO = 2.00 (2) Å and n _LiO = 6.0 (2), respectively, indicating that hexaaqua Li⁺ is dominant in the dilute solution. These results clearly indicate that a concentration dependence of the hydration number of Li⁺ occurs in the aqueous solutions.     

Partial pair correlation functions of low-density supercritical water determined by neutron diffraction with the H/D isotopic substitution method

Neutron diffraction measurements were carried out on H/ D isotopically substituted water in the low-density supercritical condition (T = 673 K, P = 26.3 MPa, and rho = 0.0068 molecules.A-3) in order to obtain direct information on the intermolecular partial structure functions, gHH inter(r), gOH inter(r), and gOO inter(r). In correspondence to the high-density supercritical water previously reported, the intermolecular nearest neighbor peaks in gHH inter(r), gOH inter(r), and gOO inter(r) are diffuse compared with the ambient ones. The nearest neighbor O...O distance (3.3 A) and its coordination number (2.6) were determined from the observed gOO inter(r). These results indicate that the orientational correlation between neighboring water molecules is considerably lost in low-density supercritical water. Small clusters involving a few water molecules are preferentially formed in low-density supercritical water, which is consistent with results obtained by previous IR and NMR studies.     

An Anti CuO2‐type Metal Hydride Square Net Structure in Ln2M2As2Hx (Ln=La or Sm,M=Ti,V, Cr,or Mn)

Using a high pressure technique and the strong donating nature of H⁻, a new series of tetragonal La₂Fe₂Se₂O₃‐type layered mixed‐anion arsenides, Ln₂M₂As₂H_x, was synthesized (Ln=La or Sm, M=Ti, V, Cr, or Mn; x≈3). In these compounds, an unusual M₂H square net, which has anti CuO₂ square net structures accompanying two As³⁻ ions, is sandwiched by (LaH)₂ fluorite layers. Notably, strong metal–metal bonding with a distance of 2.80 Å was confirmed in La₂Ti₂As₂H_2.3, which has metallic properties. In fact, these compounds are situated near the boundary between salt‐like ionic hydrides and transition‐metal hydrides with metallic characters.