The reactivity of sulfur dioxide with transition metal complexes containing 4-cyanopyridine- and 3-pyridylcarbinol-N-oxide: the high temperature isolation of a manganese(II) iodide SO2-adduct

The reactivity of metal complexes M(RPyO)_nX₂(H₂O)_m (RPyO=4-cyanopyridine-N-oxide or 3-pyridylcarbinol-N-oxide; M=Mn, Co, Cu; X=Cl, Br, I, NO₃; n=2–4 and m=0–3) with SO₂ has been studied in toluene slurries and in the solid state at room temperature and in the solid state at high temperature. Only the metal iodide precursors containing 4-CNPyO reacted with SO₂ in the solid state or in a toluene slurry but never above room temperature. Among the precursors containing 3-HOH₂CPyO, only the copper metal complexes interact with SO₂ at room temperature in toluene slurries. Surprisingly, Mn(3-HOH₂CPyO)₂I₂(H₂O) reacted with SO₂ at 210°C, whereas the metal complex was unreactive at room temperature. Likewise, Cu(3-HOH₂CPyO)₂(NO₃)₂ reacted at 100°C, the SO₂ being oxidised to sulfate, displacing the nitrate group, but not at room temperature.     

A structure, conductivity and dielectric properties investigation of A3CoNb2O9 (A=Ca, Sr, Ba) triple perovskites

The room temperature structures as well as the temperature-dependent conductivity and dielectric properties of the A₃CoNb₂O₉ (A=Ca²⁺, Sr²⁺ and Ba²⁺) triple perovskites have been carefully investigated. A constrained modulation wave approach to Rietveld structure refinement is used to determine their room temperature crystal structures. Correlations between these crystal structures and their physical properties are found. All three compounds undergo insulator to semiconductor phase transitions as a function of increasing temperature. The hexagonal Ba₃CoNb₂O₉ compound acts as an insulator at room temperature, while the monoclinic Ca₃CoNb₂O₉ compound is already a semiconductor at room temperature. The measured dielectric frequency characteristics of the A=Ba compound are excellent.     

Raman Investigation of the Low Temperature Phase Transitions in Monoclinic TlReO4

The Raman spectrum of monoclinic TlReO₄ is presented together with a factor group analysis and assignment of the bands. The phase transitions of monoclinic TlReO₄ is investigated below room temperature, and two phase transitions were identified between room temperature and 90 K. The room temperature monoclinic phase was converted to the orthorhombic phase at 170 K upon cooling, and to the tetragonal phase at 150 K. Upon heating back to room temperature the tetragonal phase persisted until the orthorhombic phase could be identified at 210 K and 220 K. From 230 K to room temperature the monoclinic phase could again be observed.     

γ-Alumina-supported boron trifluoride: Catalysis, radiotracer studies and computations

The irreversible adsorption of boron trifluoride on calcined γ-alumina and amorphous chromia, in both cases at room temperature, has been studied using [¹⁸F]-labelled BF₃. Although the resulting γ-alumina surface has some catalytic activity for the room temperature fluorination by anhydrous HF of CH₃CCl₃ under static conditions, its activity is far lower than that of γ-alumina, which has been fluorinated with SF₄, nominally at room temperature. A possible explanation for the observed behaviour is given.     

Room-temperature monoclinic and low-temperature triclinic phase-transition structures of meso-octa­methyl­calix­[4]­pyrrole–di­methyl sulfoxide (1/1)

Crystals of the title complex, C₂₈H₃₆N₄·C₂H₆OS, undergo a phase transition between room temperature and 198 K, as determined by X-ray diffraction techniques. A monoclinic form is observed at room temperature, while a triclinic modification is found at 198 K, with Z′ changing from 1 to 2. Differential scanning calorimetry (DSC) of the calix­pyrrole–di­methyl sulfoxide complex revealed a series of phase changes between 273 and 243 K. The transition from the room-temperature monoclinic form to the low-temperature triclinic form is reversible, as determined by changes in the cell dimensions from remeasuring selected reflections at room temperature and at temperatures below 223 K. The uncomplexed calix­[4]­pyrrole mol­ecule shows no phase changes occurring between room temperature and 233 K, the low-temperature limit of the DSC.     

Vibrational characterization of the compound (C2H5NH3)2PdCl4(EAPdC)

The NIR and IR transmission spectra at room temperature of single crystals of (C₂H₅NH₃)₂PdCl₄ (EAPdC) have been measured, as well as unpolarized Raman spectra at room and liquid-nitrogen temperature. These vibration spectra are compared with those of EACuC and EACdC. We conclude that EAPdC belongs to the family of compounds EAMC, where M = Mn, Cu, Cd.     

In and F MAS NMR study of (NH4)3InF6 phases

This study presents for the first time an NMR spectroscopic characterization of the room and high temperature phases of (NH₄)₃InF₆ using ¹⁹F and ¹¹⁵In as probe nuclei. The reversible phase transition to the cubic phase at 353 K was followed by MAS NMR in situ. Static NMR experiments of the room temperature phase and MAS NMR experiments of the high temperature phase allowed the determination of the NMR parameters of both nuclei. Finally, the scalar In-F coupling, rarely observed in solid state NMR, is evidenced in both room and high temperature phases of (NH₄)₃InF₆, and measured in the high temperature phase.     

Role of surface hydroxyl groups in promoting room temperature CO sensing by Pd-modified nanocrystalline SnO2

SnO₂/Pd nanocomposites were synthesized via sol-gel method followed by variable processing procedures. The materials are sensitive to CO gas in the concentration range 2-100 ppm at room operating temperature. It was shown that modification of nanocrystalline tin dioxide by Pd changes the temperature dependence of sensor response, decreasing the temperature of maximal signal. To understand the mechanism of room temperature CO sensitivity, a number of SnO₂/Pd materials were characterized by XRD, TEM, BET, XPS and TPR techniques. From the results of FTIR, impedance and sensing measurements under variable ambient conditions it was concluded that improvement in CO sensitivity for Pd-modified SnO₂ is due to alteration of CO oxidation pathway. The reaction of CO with surface OH-groups at room temperature was proposed, the latter being more reactive than oxygen species due to the possible chain character of the reactions. It was proposed that Pd additive may initiate chain processes at room temperature.     

无溶剂中性条件下分子I2或Fe(NO3)3·9H2O/NaI原位生成的I2催化醇与甲酸甲酰化反应

 Different alcohols were formylated by formic acid under solvent-free conditions in the presence of iodine as the catalyst with good-to-high yields at room temperature. I₂ generated in situ from Fe(NO₃)₃·9H₂O/NaI also catalyzed the formylation of the alcohols under solvent-free conditions. This gives a green and efficient reaction at room temperature, in which the use of toxic and corrosive molecular I₂ is avoided.     

Free radicals in γ-irradiated poly-α-methylstyrene

Electron spin resonance (ESR) spectra were observed at ?160°C and at room temperature for γ-irradiated poly-α-methylstyrene. The spectrum observed at room temperature has been attributed to the radical species while that at ?160°C results from the same radical and superposition of the spectrum due to the radical ?H₂-C(CH₃)(C₆H₅)-. The radicals which are stable at room temperature could be used to graft vinyl acetate.     

Photolysis of 1,1,1-trifluoromethylazomethane as a source of methyl and trifluoromethyl radicals

The photochemistry of 1,1,1-trifluoromethylazomethane has been partially characterized. The quantum yield for N₂ formation from photolysis at 366 nm and room temperature was unity at low pressure and decreased to 0.5 at 630 torr. At room temperature the principal products were C₂H₆, C₂F₆, CH₃CF₃ (or CH₂CF₂ + HF at reduced pressures), plus substituted hydrazines, which mainly arise from addition of CF₃ to the parent followed by combination of these radicals with CH₃ or CF_3. These fluorinated methyl hydrazine products detract from the general utility of CF₃-N₂-R compounds as sources for simultaneous study of the chemistry of CF₃ and R radicals. At room temperature the hydrazine products accounted for more than 50% of the total yield; however, these products can be reduced by lowering the temperature and at 195°K their yields are negligible. The quantum yield for intramolecular (direct) formation of CH₃CF₃ + N₂ was shown to be ≤0.002.     

SO4 2−/SnO2: Efficient,Chemoselective, and Reusable Catalyst for Acylation of Alcohols,Phenols, and Amines at Room Temperature

Abstract

SO₄ ^2?/SnO₂ was employed for the acylation of a variety of alcohols, phenols, and amines under solvent‐free conditions at room temperature. This method showed preferential selectivity for acetylation of the amino group in the presence of a hydroxyl group. The reported method is simple, mild, and environmentally viable, using several other acid anhydrides at room temperature.     

Hierarchical Ni−Al hydrotalcite supported Pt catalyst for efficient catalytic oxidation of formaldehyde at room temperature

Catalytic oxidation at room temperature is recognized as the most promising method for formaldehyde (HCHO) removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. Herein, flower-like hierarchical Pt/NiAl-LDHs catalysts with different [Ni²⁺]/[Al³⁺] molar ratios were synthesized via hydrothermal method followed by NaBH₄ reduction of Pt precursor at room temperature. The flower-like hierarchical Pt/NiAl-LDHs were composed of interlaced nanoplates and metallic Pt nanoparticles (NPs) approximately 3–4 nm in diameter were loaded on the surface of the Pt/NiAl-LDHs with high dispersion. The as-prepared Pt/NiAl21 nanocomposite was highly efficient in catalyzing oxidation of HCHO into CO₂ at room temperature. The high activity of the hierarchical Pt/NiAl21 nanocomposite was maintained after seven recycle tests, suggesting the high stability of the catalyst. Based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies, a reaction mechanism was put forward about HCHO decomposition at room temperature. This work provides new insights into designing and fabricating high-performance catalysts for efficient indoor air purification.     

Surface complexation by caesium fluoride. The case of sulphur tetrafluoride

The heterogeneous, room temperature complexation reaction between caesium fluoride and sulphur tetrafluoride is conveniently observed using ¹⁸F and ³⁵S radiotracer methods. The major surface species is weakly adsorbed SFe₄, SF₅^? being a minor species. Neither undergo observable ¹⁸F exchange with CsF at room temperature.     

Comparative study of H2S and SO2 adsorption on polycrystalline copper by surface potential measurements

Surface Potential Variations ΔΦ and XPS show the presence of S(a) on Cu after exposure to H₂S. On such a presulfided state, H₂S adsorbs molecularly and reversibly at room temperature. Exposure to SO₂ mainly leads to the formation of S(a) and SO_x(a) while molecular adsorption has not been evidenced at room temperature.     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.     

沉淀法制备不同形貌和结构的纳米BiVO4

采用液相沉淀法，通过选择不同起始原料并控制反应温度和pH值，制备得到不同形貌和结构的纳米BiVO₄。采用X-射线衍射(XRD)、透射电子显微镜(TEM)和紫外-可见吸收光谱(UV-Vis)技术对产物进行分析表征。结果表明，采用NH₄VO₃作V源，室温下可直接制备得到结晶好的四方晶系硅酸锆型BiVO₄球形纳米颗粒，提高反应液pH值或升高温度，可得到单斜晶系白钨矿型BiVO₄，采用NaVO₃作为V源，室温下可直接得到单斜晶系白钨矿型片状BiVO₄。加入不同类型表面活性剂则得到不同形貌的BiVO₄。     

Yellow-green luminescence and extreme thermal quenching in the Sr6M2Al4O15:Eu2+ (M = Y,Lu, Sc) phosphor series

A series of Eu²⁺-substituted yellow-green emitting phosphors based on the compound, Sr₆M₂Al₄O₁₅ (M = Y, Lu, Sc) were identified as potential efficient phosphors based on their high calculated Debye temperatures (Θ_D > 450 K), which acts as a proxy for photoluminescent quantum yield (PLQY). The crystal structure contains corner-sharing [MO₆] octahedra and [AlO₄] tetrahedra leading to a highly connected, densely packed crystal structure. However, contrary to prediction, these compounds all showed a low PLQY (<6.5%) at room temperature. Temperature dependent luminescence measurements indicate that the photoluminescence is intense at 80 K but loses ≈90% of the emission intensity by room temperature, with the thermal quenching temperature (T₅₀) occurring well below room temperature. These results suggest that even though Debye temperature (Θ_D) is a valid proxy for PLQY, it does not describe thermal quenching.     

A new room temperature ionic liquid of oxyfluorometallate anion: 1-Ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF5)

The first room temperature ionic liquid (room temperature molten salt) containing oxyfluorometallate anion, 1-ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF₅), has been synthesized and characterized compared to other known EMIm fluorocomplex salts. EMImWOF₅ is synthesized by two routes: one is the hydrolysis of EMImWF₇ and the other is the fluoroacid-base reaction of EMIm(HF)_2.3F and WOF₄. EMImWOF₅ is a hydrophilic room temperature ionic liquid but is stable in aqueous solution. From the result of DSC analysis, EMImWOF₅ exhibits a glass transition at 182 K and melts at 253 K. The density, conductivity and viscosity at 298 K are 2.25 g cm⁻³, 3.0 mS cm⁻¹ and 105.1 cP, respectively.     

A simplified synthesis of the hexamethylplatinate(IV) ion

Tetra-n-butylammonium hexachloroplatinate (IV) reacts with lithium methyl/lithium iodide in ether to give a solution containing lithium hexamethylplatinate (IV). With lithium methyl/lithium bromide in ether however, tetrabutylammonium hexamethylplatinate (IV) is precipitated together with lithium halides. Solid [Bu₄N)₂[Pt(Ch₃)₆] is stable under nitrogen at room temperature, but ether solutions of [Pt(Ch₃)₆]^2- decompose in a few minutes at room temperature in the absence of excess lithium methyl.