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.     

(±)-3-(3-Oxo­cyclo­hexyl)­propionic acid: dual conformational selection and hydrogen bonding in an ɛ-keto acid

The asymmetric unit of the title compound, C₉H₁₄O₃, consists of two mol­ecules having conformations that differ by a rotation of 111.7 (5)° about the equatorial substituent bond, so that the side chains of the two species extend away from the ring in different directions. Each conformer forms centrosymmetric hydrogen-bonded acid-to-acid dimers with its own enantiomer [O⋯O = 2.681 (3) and 2.698 (4) Å]. There is an intermolecular C—H⋯O close contact involving the ketone group of one of the conformers.     

Phase and extraction equilibria in water–polyethyleneglycol ethers of monoethanolamides of synthetic fatty acid–ammonium chloride systems

Phase equilibria in layering systems of water, polyethyleneglycol ethers of monoethanolamides of synthetic fatty acids (SFAs) (synthamide-5), and ammonium chloride are studied. The possibility of using such systems for the liquid extraction of metal ions is evaluated. The effect the nature of salting-out agents has on the processes of segregation of the systems has been considered.     

UV absorption of n-alkyl 1-thio-β-d-glucopyranosides and its utilization in chromatographic separation

The UV absorption of n-alkyl β-d-glucopyranosides has not been utilized so far for their detection which is usually performed by means of the refractive index detector. In this paper, we demonstrate the HPLC separation of several n-alkyl β-d-glucopyranosides with linear gradient by using UV detector and support our findings with time-dependent density functional theory calculations.     

Phase transitions in poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate). SAXS,WAXS and DSC study

The main-chain thermotropic liquid-crystalline poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate) (P7MB) was investigated by time-resolved small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimerty (DSC). Nonisothermal crystallisation with different rates of cooling and heating was used. On cooling, two phase transitions are observed, isotropic melt - smectic (I-Sm) and Sm- three-dimensional crystalline structure (Sm-Cr), whereas on heating only one transition is observed, Cr-I transition. The transition enthalpies were calculated. Temperature dependences of d-spacings of all crystalline peaks and of the peak observed at high values of scattering vector in the SAXS region were derived. The temperature dependence of the degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo in WAXS.     

Vibrational spectrum and hydrogen bonding in solid α-naphthol

The i.r. spectrum of α-naphthol has been obtained at different temperatures and at different degrees of deuteration. A method is proposed for determining the orientation of the crystallographic axis with respect to the incident beam. The absorption bands due to hydrogen bonded groups are then analysed in terms of a simple dipole-dipole model.     

Bis(O,O′-diiso­propyl di­thio­phosphato-S,S′)(1,10-phenanthroline-N,N′)metal(II) complexes with cadmium(II) and iron(II)

The two title compounds, [M(C₆H₁₄O₂PS₂)₂(C₁₂H₈N₂)], where M = Cd^II and Fe^II, are isomorphous. Each compound has a crystallographic twofold axis of symmetry through the metal atom and the 1,10-phenanthroline mol­ecule. The central metal atom is coordinated to four S atoms from the two dithiophos­phate groups and two N atoms from the 1,10-phenanthroline ligand. The environment of the metal atom is a distorted octahedron.     

Phase transitions,structures, and rheological properties of hydroxypropyl cellulose–ethylene glycol and ethyl cellulose–dimethylformamide systems in the presence and in the absence of a magnetic field

Phase transitions, structures, and rheological properties of hydroxypropyl cellulose–ethylene glycol and ethyl cellulose–dimethylformamide systems in the presence and in the absence of a magnetic field have been studied. The application of the magnetic-field results in increases in viscosity and supramolecular particle size in solutions of cellulose ethers. Concentration dependences of viscosity and particle size are described by curves with maxima.     

Reactivity of Mg–Al hydrotalcites in solid and delaminated forms in ammonium carbonate solutions

Treatment of Mg–Al hydrotalcites (LDHs, layered double hydroxides) in aqueous (NH₄)₂CO₃ at 298 K leads to composites of dawsonite, hydrotalcite, and magnesium ammonium carbonate. The mechanism and kinetics of this transformation, ultimately determining the relative amounts of these components in the composite, depend on the treatment time (from 1 h to 9 days), the Mg/Al ratio in the hydrotalcite (2-4), and on the starting layered double hydroxide (solid or delaminated form). The materials at various stages of the treatment were characterized by inductive coupled plasma-optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetry, and nitrogen adsorption at 77 K. The progressive transformation of hydrotalcite towards crystalline dawsonite and magnesium ammonium carbonate phases follows a dissolution–precipitation mechanism. A gradual decrease of the Mg/Al ratio in the resulting solids was observed in time due to magnesium leaching in the reacting medium. Dawsonite–hydrotalcite composite formation is favored at high aluminum contents in the starting hydrotalcite, while the formation of magnesium ammonium carbonate is favored at high Mg/Al ratios. The synthetic strategy comprising hydrotalcite delamination in formamide prior to aqueous (NH₄)₂CO₃ treatment is more reactive towards composite formation than starting from the bulk solid hydrotalcite.     

Phase equilibria of supercritical CO_2-ethanol-stearic acid ternary system and hydrogen bonding between ethanol and stearic acid

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Hydrogen absorption and phase transitions in rapidly quenched LaNi alloys

Several LaNi binary alloys were rapidly quenched by melt spinning. A metastable phase and an uniform Laves phase were obtained. Differences in behaviour were observed between hydrogenation of quenched materials and of as-cast materials whose compositions were identical. The quenched materials, in contrast to the as-cast phases, had a tendency to form amorphous LaNiH alloys. The amorphous alloy was stable, in particular when the ratio La:Ni was 1:2.     

Liquid–liquid equilibria of aqueous two-phase systems containing polyethylene glycol and ammonium dihydrogen phosphate or diammonium hydrogen phosphate. Experiment and correlation

Phase diagrams and liquid–liquid equilibrium (LLE) data of the aqueous systems polyethylene glycol 6000 (PEG₆₀₀₀)–ammonium dihydrogen phosphate and aqueous PEG₆₀₀₀–diammonium hydrogen phosphate have been determined experimentally at 298.15, 308.15 and 318.15 K. Furthermore, the osmotic virial equation was used to correlate the phase behavior of these systems. Good agreement was obtained with the experimental data. Finally, the effect of temperature and the type of salt on the LLE are discussed.     

Five- and six-membered N-H?S hydrogen bonding in aromatic amides

The capacity of sulfur to form intramolecular five- or six-membered S?H-N hydrogen bonding in aromatic amides is assessed. The five-membered S?H-N hydrogen bonding is observed in crystal structures of five compounds, whereas the six-membered S?H-N hydrogen bonding is revealed in crystal structures of three compounds. The trityl group has been used to promote formation of the weak hydrogen bonding because it efficiently inhibits the competition of the intermolecular CO?H-N hydrogen bonding. (2D) ¹H NMR experiments indicate that both patterns also exist in chloroform.     

Phase transition of the NH4Br—NH4I mixed crystals and librational motion of the ammonium ion

Far-infrared study on the NH₄BrNH₄I mixed crystals revealed the librational frequencies of 314 cm⁻¹ for 1 (bromide):3 (iodide) and of 322 cm⁻¹ for 1:1 crystals. The phase transitions of the 1:3 mixed crystal occurred at around 205 and 235 K. The potential barrier heights for the NH⁺₄ librations have been estimated to be 3.58 and 3.83 kcal/mol for the 1:3 and 1:1 mixed crystals, respectively.     

Phase relations and equilibrium copolymerization in the SeS system

The phase relations in the SeS system were investigated by the appearance of phase method, differential thermal analysis, and differential scanning calorimetry. High purity selenium melts at 216 ± 2°C. A peritectic exists at 85 at. % Se and 168 ± 2°C; the peritectic isotherm extends from 92 to 73.5 at. % Se. A temperature minimum of 102 ± 1°C exists at a composition of 35 ± 1 at. % Se. High purity sulfur melts at 114 ± 1°C and polymerizes at 160 ± 2°C. Addition of 10 at. % Se lowers the polymerization temperature to 118 ± 3°C. The SeS system shows complete liquid miscibility and in this respect it differs from the majority of selenide type systems that generally show one or more fields of liquid immiscibility. The complete liquid miscibility in the SeS system can best be explained by the equilibrium copolymerization theory. Investigation of the subsolidus relations in the SeS system shows a miscibility gap in the Se-rich part of the system. The eutectoid proposed by W. E. Ringer (Z. Anorg. Chem. 32, 183 (1902)) in the S-rich part of the system was not detected.     

Phase separation in mixtures of thermotropic liquid crystals and flexible polymers

The spinodal equation and the concentration-induced anisotropic-isotropic transition equation of the mixtures of thermotropic liquid crystals and flexible polymers have been studied by using the molecular field theory The calculations of the phase diagrams of this system show that,besides the isotropic classic spinodal curve,there ex ists an anisotropic spinodal curve which has not been reported in literature.These two spinodal curves can be linked up by the concentration-induced anisotropic-isotropic transition line.In the various phase regions,demixing may take place due to different phase separation mechanisms.The phase equilibrium curve cannot always join the.spinodal curve at a critical point.These results are considered very meaningful for the understanding of the special properties of liquid crystal/polymer composites and very useful for controlling the morphology and the performance of PDLC materials     

Phase behavior of dodecane–hexadecane mixtures in bulk and confined in SBA-15

Phase behaviors of dodecane–hexadecane (n-C₁₂H₂₆–C₁₆H₃₄, C₁₂–C₁₆) binary mixtures in bulk and confined in SBA-15 (pore diameters 3.8, 9.5, and 17.2 nm) are investigated using differential scanning calorimetry. According to the thermal analysis, the bulk mixtures belong to a system of partial miscibility with two solid solutions and a eutectoid in the range of mole fraction $ x_{{{\text{C}}_{ 1 6} }} $  = 0.1–0.8. Under confinement, phase behavior of C₁₂–C₁₆ mixtures is distinct from the bulk. Inside pores of SBA-15 (3.8 nm), the solid mixtures has only a melting boundary. In the pores larger than 9.5 nm, phase behaviors of the mixtures show some resemblance to the bulk system. The growth of the phase diagram with the pore diameter clearly shows the size effect on the phase behavior of the confined mixtures. In comparison with those of chain length difference of pure components of two carbon atoms or less, C₁₂–C₁₆ mixtures exhibit different phase behaviors not only in the bulk but also in the confined state.     

Seeking for ultrashort “non-bonded” hydrogen–hydrogen contacts in some rigid hydrocarbons and their chlorinated derivatives

In this communication a systematic computational survey on some rigid hydrocarbon skeletons, e.g., half-cage pentacyclododecanes and tetracyclododecanes, and their chlorinated derivatives to seek for the so-called ultrashort “non-bonded” hydrogen–hydrogen contacts is done. It is demonstrated that upon a proper choice and modifications of the main hydrocarbon backbones, and addition of some chlorine atoms instead of the original hydrogen atoms in parts of the employed hydrocarbons, the resulting strain triggers structural changes yielding ultrashort hydrogen–hydrogen contacts with inter-nuclear distances as small as 1.38 Å. Such ultrashort contacts are clearly less than the world record of an ultrashort non-bonded hydrogen–hydrogen contact, 1.56 Å, very recently realized experimentally by Pascal and coworkers in in,in-bis(hydrosilane) (J Am Chem Soc 135:13235, 2013). The resulting computed structures, as well as the developed methodology for structure design open the door for constructing a proper set of molecules for future studies on the nature of the so-called non-bonded hydrogen–hydrogen interactions that is now an active and controversial area of research.