Energetic properties of nio surface examined by heat-of-adsorption measurement

Heat of adsorption and isotherm of water vapor on NiO samples were measured simultaneously at 301 K to examine the energetic properties of the surface. They revealed that NiO has a relatively uniform surface. The heat of adsorption ranging 80–90 kJ·mol^–1 indicates the production of surface hydroxyl groups on the (100) plane of NiO. It is relatively small compared with that of other metal oxides, which suggests a weak nature of the Ni²⁺ ion sites for chemisorption of water. It is suspected that half of the surface Ni²⁺ ions are covered with hydroxyl groups and the remainings act as relatively strong physisorption sites for water molecules.The authors are grateful for the help of Prof. S. Kittaka of Okayama University of Science in taking electron micrographs. This work was partly supported by Grant-in-Aid for Scientific Research No. 02640348 from the Ministry of Education, Science and Culture of Japanese Government.     

Stability of naturally occurring pyrazines and construction route of pyrazine rings

Naturally occurring pyrazines fit well the theory that conformity to the TCS rule gives a stable molecular system. Thus, many pyrazines so far synthesized and those in nature which are energetically very stable molecules can be synthetically quite accessible. The TCS rule applies very well to the construction route of pyrazine rings.     

Mössbauer study of the transition metal phosphorus trichalcogenide FePS3 and spin glass Mn0.5Fe0.5PS3

The transition metal phosphorus trichalcogenides MnPS₃ and the FePS₃ are CdCl₂ type layered compounds, where the transition metal ions form a hexagonal lattice. While these compounds order anti-ferromagnetically at low temperature, the magnetic structures are different. We have reported that these mixtures Mn_0.5Fe_0.5PS₃ is a spin glass with a glass transition temperature T _g=33.7 K. Then, in this work, we report that the results of the temperature variation of the ⁵⁷Fe Mössbauer spectra of FePS₃ and Mn_0.5Fe_0.5PS₃, in detail. In the anti-ferromagnetic state of FePS₃, the hyperfine magnetic field H _int increases with decreasing temperature and the Isomer shift I. S. increases slightly with decreasing temperature. However in Mn_0.5Fe_0.5PS₃, the two broadened peaks are observed and the two peaks became a single peak with decreasing temperature at about 50.0 K, which is higher than T _g=33.7 K. In the spin glass Mn_0.5Fe_0.5PS₃, the Mössbauer spectra suggest that the magnetic interactions exist far above T _g.     

Phase behavior of binary mixtures composed of ethylene carbonate and various organic solvents

Phase behaviors of the binary mixtures composed of ethylene carbonate (EC) and aliphatic alcohols, ω-phenyl alcohols, and alkylbenzenes were investigated. In addition, heat of solution of EC into these organic solvents was measured. The EC/methanol and EC/ethanol systems gave homogeneous solution at the temperature above their liquidus lines, while the mixtures of EC and alcohols with longer alkyl chain showed a miscibility gap in a liquid phase and provided the monotectic-type phase diagram. The liquid–liquid phase separation region expanded with the increase in the alkyl chain length. A similar phase behavior was also observed for the mixtures of EC and alkylbenzenes. On the other hand, the EC mixtures with ω-phenyl alcohols showed no miscibility gap in a liquid phase at least up to 4-phenylbutan-1-ol which has C4 alkyl chain intervening between phenyl and hydroxyl groups. This result demonstrates that both of the hydroxyl and phenyl groups act to facilitate the mixing of aliphatic compounds with EC. The phase behavior of these EC mixtures was analyzed applying the modified regular solution model in which the pair interaction energy was regarded as free energy. The model calculation with the use of heat of solution of EC at infinite dilution as the pair interaction enthalpy reproduced well both of the experimentally obtained liquidus line and mutual solubility curve as well as monotectic point.     

Organic reactions mediated by electrochemically generated ArS+

Low-temperature electrochemical oxidation of ArSSAr was carried out to generate a pool of "ArS(+)". Spectroscopic studies ((1)H NMR and CSI-MS) of the resulting solution revealed the accumulation of ArS(ArSSAr)(+). The resulting "ArS(+)" pool reacted with alkenes and alkynes to give diarylthio-substituted products. The "ArS(+)" pool rapidly reacted with thioacetals to give the corresponding alkoxycarbenium ion pools, which reacted with various carbon nucleophiles (indirect cation pool method). The reaction of the alkoxycarbenium ion pools with stilbene derivatives in the presence of ArSSAr gave thiochroman derivatives. In addition to such stoichiometric reactions, a catalytic amount of "ArS(+)" serves as an initiator and a chain carrier of some cationic chain reactions involving intramolecular carbon-carbon bond formation. In situ generation of "ArS(+)" by electrochemical oxidation of ArSSAr with a catalytic amount of electricity in the presence of a substrate is also effective for such cationic chain reactions.     

High-pressure hydrothermal crystal growth and multiferroic properties of a perovskite YMnO3

Orthorhombic perovskites RMnO(3) are representative of spin-driven ferroelectrics. When the radius of the rare-earth ion R is smaller than that of Dy, for instance in YMnO(3), the orthorhombic phase becomes metastable at ambient pressure, which impedes the crystal growth; thus, the detailed magnetic and multiferroic properties of the metastable phase have not been characterized. In this work, we successfully obtained single crystals of orthorhombic YMnO(3) using quasi-hydrothermal conditions under a high pressure of 5.5 GPa. Magnetic and dielectric measurements under magnetic fields revealed that the magnetic ground state is the commensurate E-type antiferromagnetic, while a cycloidal spin phase likely coexists in the intermediate temperature range, which enhances the magnetoelectric response to external fields.     

Properties of ionic liquids containing silver(I) or protic alkylethylenediamine cations with a bis(trifluoromethanesulfonyl)amide anion

Ionic liquids of an N-alkylethylenediamine-silver(I) complex cation (alkyl=hexyl, 2-ethylhexyl, and octyl) or a protic N-alkylethylenediaminium cation (alkyl=butyl, hexyl, 2-ethylhexyl, octyl, decyl, and dodecyl) with a bis(trifluoromethanesulfonyl)amide counter anion (Ag-ILs and PILs, respectively) were prepared and their physicochemical properties were investigated. The trend of solidification decreased in the order octyl?hexyl>2-ethylhexyl for the Ag-ILs, and butyl>dodecyl>decyl>octyl>hexyl?2-ethylhexyl for the PILs. The diffusion coefficients of the cations indicated stronger intermolecular interactions in PILs than in the Ag-ILs because of hydrogen-bonding networks, and it has been revealed that the intermolecular interactions increase in the order, hexyl相似文献   

Oxidation of annelated diarylamines: analysis of reaction pathways to nitroxide diradical and spirocyclic products

Oxidation of diaryldiamine 2, a tetrahydrodiazapentacene derivative, provides diarylnitroxide diradical 1 accompanied by an intermediate nitroxide monoradical and a multitude of isolable diamagnetic products. DFT-computed tensors for EPR spectra and paramagnetic (1)H NMR isotropic shifts for nitroxide diradical 1 show good agreement with the experimental EPR spectra in rigid matrices and paramagnetic (1)H NMR spectra in solution, respectively. Examination of the diamagnetic products elucidates their formation via distinct pathways involving C-O bond-forming reactions, including Baeyer-Villiger-type oxidations. An unusual diiminoketone structure and two spirocyclic structures of the predominant diamagnetic products are confirmed by either X-ray crystallography or correlations between DFT-computed and experimental spectroscopic data such as (1)H, (13)C, and (15)N NMR chemical shifts and electronic absorption spectra.