四氯合金属(II)酸烷铵在280-500K间的热力学性质和相变 I:四氯合锰(II)酸n-十二烷铵

在280-500K的温度范围内用自动绝热量计测定了(n-C12HxNH3)2MnCl4的热容.发现了两个固-固相变,固ID→固II和固I→固II.前者的相变温度、相变焓和相变熵分别为330.6±0.1K,47.78±0.29kJ.mol^-^1和144.5±0.9J.K^-^1.mol^_^1,后者的对应相变热参数分别为334.5±0.1K,5.96±0.05kJ.mol^-^1和17.82±0.15J.K^-^1.mol^-^1.报道了该物质每隔10K的热力学性质.     

Liquid crystalline phase transitions in hexakis(4-(4'-heptyloxy)biphenoxy)cyclotriphosphazene

Hexakis(4-(4'-heptyloxy)biphenoxy)cyclotriphosphazene (HHCP) was synthesized from hexachlorocyclotriphosphazene and 4-heptyloxy-4'-hydroxybiphenyl. The mesogenicity of HHCP was studied by DSC, FTIR spectroscopy and polarizing microscopy. Enantiotropic smectic C and nematic phases were observed between 450 and 455 K and 455 and 456 K, respectively, on heating, and between 456 and 455 K (nematic) and 455 and 440 K (smectic C) on cooling from the isotropic liquid phase. The introduction of the heptyloxybiphenoxy groups as side chains into cyclotriphosphazene has generated the liquid crystalline phase. FTIR spectroscopy showed that the P=N and P-O-(C) stretching vibrations converted to lower frequencies from 1224 to 1210 cm^-1 and from 920 to 910cm^-1, respectively, at the crystalline (C)-S_c phase transition. This result suggests that the state of the cyclotriphosphazene ring dramatically changes near the C-S_c phase transition.     

Vapor pressure and heat capacities of perfluoro-<Emphasis Type="Italic">N</Emphasis>-(4-methylcyclohexyl)piperidine

Heat capacities of perfluoro-N-(4-methylcyclohexyl)piperidine (PMCP) have been measured by low-temperature adiabatic calorimetry. The purity of the compound, its triple-point temperature, and its enthalpy and entropy of fusion have been determined. The saturated vapor pressure was determined by comparative ebulliometry as a function of temperature in the 6.2–101.6 kPa pressure range and 374.2–460.9 K temperature range. The calorimetric enthalpy of vaporization at T = 298.15 K has been measured. The following thermodynamic properties were calculated for PMCP: normal boiling temperature, enthalpy of vaporization Δ_vap H _m ⁰ (T) as a function of temperature, and critical parameters. The enthalpies of vaporization at 298.15 K obtained experimentally and by calculation methods match within their error limits, which validates their adequacy and the adequacy of the Δ_vap H _m ⁰ = f(T) equation as an extrapolation.     

4-(4-吗啉)哌啶盐酸盐的合成

4-甲酸乙酯哌啶与溴苄反应,再经酰胺化和氨化反应制得关键中间体4-氨基-1-苄基哌啶(5);5与2,2-二溴二乙醚经环化反应制得N-苄基-4-(4-吗啉)哌啶,再经成盐,加氢合成了4-(4-吗啉)哌啶盐酸盐(1,总收率24.9%),1的结构经1HNMR,IR和GC-MS确认。     

Raman spectra and phase transitions in single crystal (NH4)2ZnCl4

Raman spectra of single crystal (NH₄)₂ZnCl₄ at 300 and 105K at different polarizations are reported and analysed in view of previously reported structural data. The experimental observations suggest that the free oriented gas model is applicable for group theoretical analysis of the vibrational modes in this system at room temperature. It is also concluded that the space group for the room temperature phase III is C²_s instead of C⁹_2v. The temperature dependence of thermosensitive bands shows discontinuities at 267 and 194 K. The structure in the new phase VI below 194 K is suggested to be triclinic.     

4-(3-氯苯乙基)呱啶的简便合成

以廉价易得的N-Boc呱啶-4-甲醇（1）和间氯苄氯（3）为原料,经Swern 氧化、Wittig反应、钯碳催化加氢和脱保护基反应合成目标化合物4-(3-氯苯乙基)呱啶盐酸盐(7)。路线总收率达到56%,化学纯度96.6%。加氢不脱氯反应的最佳反应条件为：以含量为10%干钯碳催化加氢,二氧六环为溶剂,反应时间3h。化合物7的结构及纯度经¹H NMR,¹³C NMR和MS（EI）确证。该合成方法具有反应条件温和、操作简单、收率高等优点。      

The structure and phase transitions in oxyfluoride (ND4)2MoO2F4

Single crystals of (ND₄)₂MoO₂F₄ containing 95% deuterium were produced by repeated recrystallization of (NH₄)₂MoO₂F₄ in heavy water. The effect of deuteration on the parameters of successive phase transitions was investigated by differential scanning microcalorimetry and polarization optics. X-ray analysis of the original and distorted phases was performed. It was found that deuteration does not change the sequence of crystal phases typical for (NH₄)₂MoO₂F₄, but leads to a shift in the phase transition Cmcm → Pnma towards the tricritical point. The mechanism of phase transitions in (ND₄)₂MoO₂F₄ was associated with both the ordering and the displacement of atoms.     

四氯合金属(II)酸正烷铵在280-500K间的热力学性质和相变 II: 四氯合锌(II)酸正十二烷铵

研究了四氯合锌(II)酸正十二烷铵(C12H25NH3)2ZnCl4(1)]在280-500K间的热力学性质和相变热参数. 据报导(RNH3)MX4型化合物在300-380K间有相变焓很大的固-固相变, 是很有开发前景的固-固相变低温储能材料, 本文为(1)的应用提供了精确的热数据.     

Vibrational study of structure and phase transitions in caesium hydrogen selenate (CsHSeO4)

The Raman and IR spectra of polycrystalline CsHSeO₄ and CsDSeO4 are investigated in the 20–450 K range. An assignment of bands due to internal and external vibrations in terms of approximate types of motions is proposed. The spectral data are used for discussing crystalline structures of different phases, the nature of structural disorder, phase transitions and conductivity.     

异薄荷醇黄原酸镍的配合物(英)

The coordination geometry around Ni atom in the homochiral bis(2-isopropyl-5-methylcyclohexyl xanthalato) nickel(Ⅱ) (1) displays an approximately square plane defined by four S atoms from two xanthalato ligands. CCDC: 252343.     

Structure and phase transitions in poly(diethylsiloxane)

The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α₁-form and presumably the “tetragonal” β₁-form) and two high-temperature modifications (the monoclinic α₂-form and the “tetragonal” β₂-form). In linear PDES the crystal - crystal transitions α₁–α₂ and β₁–β₂ occur near 214 and 206 K, respectively. At higher temperatures α₂ (280 K) and β₂ (290 K) forms transform into the mesomorphic phase α_m that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, α_m phase is also characterized by monoclinic structure slightly different from hexagonal packing.     

Thermal phase transitions in antimony (III) oxides

Previous reports of the thermal behaviour of antimony trioxide show significant disagreement on the values for the temperatures associated with specific thermal events. In this reappraisal, samples of both polymorphs of Sb₂O₃ (senarmontite and valentinite) have been analysed using X-ray diffraction and simultaneous differential thermal/thermogravimetric analysis techniques. The senarmontite-valentinite phase transition has been observed to occur as a multi-stage event commencing at temperatures as low as 615±3 °C—evidence of oxidation to Sb₂O₄ under inert atmosphere may indicate that the depression is related to surface- or bulk-bound water. Valentinite produced by mechanical milling of senarmontite exhibits the reverse phase transition to senarmontite at a lower than normal temperature (445±3 °C). Oxidation temperatures of 531±4 °C for senarmontite and 410±3 °C for mechanically derived valentinite were also recorded.     

DSC studies of phase transitions in poly(diethylsiloxane)

The differential scanning calorimetry studies have shown that high-molecular linear poly(diethylsiloxane) can exist in two high-temperature polymorphs which melt at 280 and 290 K. The heats of fusion of the high-temperature polymorphs are 17 and 21 J/g, respectively. Each of the high-temperature forms arises from the corresponding low-temperature form the corresponding low-temperature form when the polymer is heated: the first at 214 K (transition heat is 28 J/g) and the second at 206 K (transition heat is 26 J/g). The mesophase formed from the molten high-temperature crystalline phases melts in a rather broad temperature range of 290 to 327 K, and the heat of this transition is 2.7 J/g. Crystallization of poly(diethylsiloxane) from the mesomorphic and the supercooled amorphous state is different. In the first case, apparently, the whole mesophase is converted to the crystalline phase and the samples have a crystallinity near 1. In the second case the crystallinity is only ca. 0.3. The temperature range in which the mesophase melts depends on the molecular weight of the polymer, presence of crosslinks and the conditions under which it has been formed, e.g., temperature.     

Thermodynamic properties of discotic mesogens: heat capacities and phase transitions of benzene-hexa-n-alkanoates

Molar heat capacities of disk-like compounds benzene-hexa-n-nonanoate (BH9) and benzene-hexa-n-decanoate (BH10) have been measured with an adiabatic calorimeter between 13 K and 390 K. Three and two different phases appeared in the solid states of BH9 and BH10, respectively. Molar entropies and transition entropies were determined and compared with those of other benzene-hexa-n-alkanoates BHn (n: 5 to 10). The odd–even effect with respect to the number of carbon atoms in a side chain of a disc-like molecule was observed in the cumulative transition entropies. The molar entropies exhibited a peculiar ‘pairing phenomenon’ between BH(2m−1) and BH(2m), where m is integer. This phenomenon is well accounted for in terms of characteristic molecular structure and packing in the crystal lattice.     

Thermodynamic parameters and sorption of U(VI) on ACSD

This paper discusses the sorption properties for U(VI) by alginate coated CaSO₄·2H₂O sepiolite and calcined diatomite earth (Kieselguhr) (ACSD). The removal of U(VI) from aqueous solution by sorption onto ACSF in a single component system with various contact times, pH, temperatures, and initial concentrations of U(VI) was investigated. The sorption patterns of uranium on the composite adsorbent followed the Langmuir, Freundlich and Dubinin-Radushkhevic (D-R) isotherms. The Freundlich, Langmuir, and D-R models have been applied and the data correlated well with Freundlich model and that the sorption was physical in nature (sorption energy, E _a = 17.05 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK ₀ vs. 1/T plots. Thermodynamic parameters (ΔH _ads = 31.83 kJ/mol, ΔS _ads = 167 J/mol·K, ΔG ^o _ads (293.15 K) = −17.94 kJ/mol) showed the endothermic heat of sorption and the feasibility of the process. The thermodynamics of U(VI) ion/ACSD system indicates the spontaneous and endothermic nature of the process. It was noted that an increase in temperature resulted in a higher uranium loading per unit weight of the adsorbent.     

Thermodynamic characteristics and the temperatures of relaxation transitions of poly(methacrylic acid)

The heat capacity of poly(methacrylic acid) containing 2.5 wt % water was measured in a vacuum adiabatic calorimeter at temperatures between 80 and 325 K. The heat capacity of anhydrous poly(methacrylic acid) was calculated, and its standard enthalpies of combustion and formation were determined. On the basis of the enthalpy of melting of the “free”-water phase, the limit of water solubility in the polymer was found calorimetrically at 273 K. The temperatures of relaxation transitions (the glass transition and the β and γ transitions) of poly(methacrylic acid) mixtures with water were determined via differential thermal analysis in the region 80–550 K. In addition, the determination of the temperatures of transitions of anhydrous poly(methacrylic acid) was performed via extrapolation to zero water content of the concentration dependences of the relaxation-transition temperatures.     

Structure and phase transitions in guanidinium halogenobismuthates(III)

Differential scanning calorimetry (DSC), dilatometric and dielectric measurements have been used to study the phase transitions in [C(NH₂)₃]₃BiBr₆. The [C(NH₂)₃]₃BiBr₆ crystal undergoes four phase transitions: at 419, 429, 475 and 495 K (on heating). The high-temperature phase transition is clearly of first-order type and its high entropy effect allows classifying it as of the order–disorder type. X-ray diffraction studies showed that [C(NH₂)₃]₃BiBr₆ crystallises in monoclinic, centrosymmetric space group, C2/c. The anionic sublattice is composed of isolated BiBr₆³⁻ octahedra. The infrared between 100 and 350 K and Raman spectra at room temperature in the frequency range related to the internal vibrations of guanidinium cations were studied for [C(NH₂)₃]₃BiBr₆, [C(NH₂)₃]₃Bi₂Br₉, [C(NH₂)₃]₃BiCl₆xCl₂ and C(NH₂)₃Cl to analyse the dynamical state of cations. At room temperature, the cations in the studied guanidinium halogenobismuthates(III) are almost rigid, so the mechanism of high-temperature phase transitions is probably connected with the release of rotation of the cations.     

Raman study of phase transitions in (n-C4H9NH3)2BiCl5

The Raman spectra of (n-C₄H₉NH₃)₂BiCl₅ were recorded and analysed from 4 K to 390 K. The phase transition (α → β) at 370 K to the metastable form is manifested by changes in the low-frequency Raman spectra, indicating the changes in the anionic structure of the crystal. The phase transition at 215 K is clearly manifested by the temperature evolution of the internal modes of the butylammonium cation. The phase transition is likely to be due to a reorientational motion of the cation.