Uniaxial negative thermal expansion induced by moiety twisting in an organic crystal

Variable temperature single-crystal X-ray diffraction reveals uniaxial negative thermal expansion (NTE) of 1,4-bis(1′-hydroxycyclopentyl)-1,3-butadiyne crystal. The length of the unit cell axis a decreases with increasing temperature, whereas the b and c axes increase. The mechanism of the negative thermal expansion in the organic crystal has been derived by analysis of the crystal structures at different temperatures. Steric adjustment of the molecules in the crystal structure requires twisting of the terminal cyclopentyl ring, which drives the contraction of one of the principal axes. © The Royal Society of Chemistry.</p

Concomitant formation of two different solvates of a hexa-host from a binary mixture of solvents (Chemical Communications (2008) (5110-5112) DOI: 10.1039/b813891e)

[No abstract available]</p

Unusual conformations of a hexa-host molecule in solvate inclusion compounds

Crystallization of the hexa-host hexakis(4-cyanophenyloxy)benzene from various solvents yields inclusion compounds which were characterized by single crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis. Although the ababab conformation of the hexa-host molecule is most commonly encountered in the crystal structures, the two unusual conformations aaabbb and aaabab were also observed in this study. Desolvation of all of these inclusion compounds produces the same apohost phase, as confirmed by powder X-ray diffraction. © 2009 American Chemical Society.</p

Concomitant formation of two different solvates of a hexa-host from a binary mixture of solvents

Crystallization of hexakis(4-cyanophenyloxy)benzene from a mixture of two different solvents produces two different solvates concomitantly, which were characterized by X-ray diffraction, thermal analysis and NMR spectroscopy. © The Royal Society of Chemistry.</p

Polymorphism of a hexa-host: Isolation of four different single-crystal phases by melt crystallization

A hexa-host compound yields at least four polymorphic forms from its melt phase. All four phases have been characterized using single-crystal X-ray diffraction; two of the phases were obtained by means of thermal stress, and the different forms exhibit conformational polymorphism. Copyright © 2008 American Chemical Society.</p

Exceptionally large positive and negative anisotropic thermal expansion of an organic crystalline material

In general, the relatively modest expansion experienced by most materials on heating is caused by increasing anharmonic vibrational amplitudes of the constituent atoms, ions or molecules. This phenomenon is called positive thermal expansion (PTE) and usually occurs along all three crystallographic axes. In very rare cases, structural peculiarities may give rise either to anomalously large PTE, or to negative thermal expansion (NTE, when lattice dimensions shrink with heating). As NTE and unusually large PTE are extremely uncommon for molecular solids, mechanisms that might give rise to such phenomena are poorly understood. Here we show that the packing arrangement of a simple dumbbell-shaped organic molecule, coupled with its intermolecular interactions, facilitates a cooperative mechanical response of the three-dimensional framework to changes in temperature. A series of detailed structural determinations at 15-K intervals has allowed us to visualize the process at the molecular level. The underlying mechanism is reminiscent of a three-dimensional (3D) folding trellis and results in exceptionally large and reversible uniaxial PTE and biaxial NTE of the crystal. Understanding such mechanisms is highly desirable for the future design of sensitive thermomechanical actuators. © 2010 Macmillan Publishers Limited. All rights reserved.</p

Reversible single-crystal to single-crystal polymorphic phase transformation of an organic crystal

Two polymorphs of a substituted dihydroanthracene derivative were prepared by crystallization from different solvents. Each polymorph is reversibly interconvertible to the other by means of a single-crystal to single-crystal phase transformation. © 2010 The Royal Society of Chemistry.</p

Anomalous thermal expansion of an organic crystal - Implications for elucidating the mechanism of an enantiotropic phase transformation

Two enantiotropic polymorphs of a dumbbell shaped molecule possess similar packing arrangements, in principle, but one of the polymorphs shows anomalously anisotropic thermal expansion while the other does not. © 2011 The Royal Society of Chemistry.</p

Single-crystal to single-crystal transformations - Guest removal and substitution in a robust solvent-templated metallocyclic compound

The formation, structure, and single-crystal to single-crystal transformations of the dinuclear metallocycle [Ag2L 2](PF6)22CH3CN (L ≤ 2,3,5,6-tetrafluoro-1,4-bis(2-methylimidazole-1-yl-methyl)benzene) are described. The acetonitrile guest molecules can be removed without loss of single crystallinity to afford a porous material. CO2 sorption isotherms were recorded at various temperatures and the structures and sorption behaviour of the crystals are compared with those of a previously reported analogous system. Upon exposure to acetone vapour, the desolvated crystals undergo a single-crystal to single-crystal transformation to form the acetone solvate. © CSIRO 2010.</p

Aggregation Behavior of Sodium Dioctylsulfosuccinate in Aqueous Ethylene Glycol Medium. A Case of Hydrogen Bonding between Surfactant and Solvent and Its Manifestation in the Surface Tension Isotherm

The dependence of critical micelle concentration (cmc) of sodium dioctylsulfosuccinate (AOT) on the amount of ethylene glycol (EG) in water + EG medium was reported to be unusual and different from that of other surfactants to the extent that the cmc of AOT in EG is lower than in water. It is yet to be understood why AOT behaves so in water + EG medium, although AOT is known to have some special properties. Hence in the present study cmc of AOT in water + EG medium in the range from 0 to 100% (by weight) EG is measured by using surface tension and fluorescence emission methods. In contrast to what was reported, this study revealed that with respect to EG amount the cmc of AOT follows the general trend and AOT has higher cmc in EG than in water. On the other hand, it was surprisingly found that a break in the surface tension isotherm occurs in the premicellar region when the amount of EG exceeds 50% rendering a bisigmoidal shape to the surface tension isotherm. UV spectral study showed that AOT and EG undergo hydrogen bonding in the premicellar region when the EG amount is ≥50% and this hydrogen bonding becomes less on adding NaCl. The density functional theory calculations also showed formation of hydrogen bonds between EG and AOT through the sulfonate group of AOT providing thereby support to the experimental findings. The calculations predicted a highly stable AOT-EG-H₂O trimer complex with a binding energy of −37.93 kcal mol^–1. The present system is an example, which is first of its kind, of a case where hydrogen bonding with surfactant and solvent molecules results in a surface tension brea