Solvent diffusion and binding in a 'nonporous' molecular crystal

Crystals of a series of solvated cadmium-based metallocycles undergo single-crystal to single-crystal transformations (SCTSCT) upon desolvation to yield an empty apohost; these transiently porous crystals then allow the diffusion of bulky solvent molecules. © 2013 The Royal Society of Chemistry.</p

Single-crystal to single-crystal transformations in discrete solvated metallocycles: The role of the metal ion

Crystals of solvated cobalt- and zinc-containing metallocycles undergo single-crystal to single-crystal (SCTSCT) transformations upon desolvation to yield their close-packed forms; this is in stark contrast to the analogous cadmium-based metallocycle, which affords an empty, transiently porous phase upon desolvation. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.</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

Solid-state structural studies of oxacalix[2]arene[2]naphthalene as a molecular tweezer

A novel oxacalix[2]arene[2]naphthalene host molecule was synthesized and crystallized from a number of solvents. In the solid state the host assumes the 1,3-alternate conformation, allowing it to function as a molecular tweezer by utilizing its naphthalene moieties as pincer arms. An apohost phase was crystallized from DMSO and single-crystal X-ray diffraction analysis reveals that the pincer arms are pinched together rather than interdigitating. Solvate crystals were obtained from dimethyl formamide, dimethyl acetamide, N-methyl pyrrolidone and nitrobenzene and these were also analyzed by means of single-crystal X-ray diffraction. Three of the solvate phases are isoskeletal with a host:guest ratio of 1:1, and with the guest molecules located between the pincer arms. The nitrobenzene solvate has a host:guest ratio of 1:2 - one of the guest molecules is complexed by the pincer arms while the second is situated interstitially. © 2011 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

Breaking the trigonal host packing motif of Dianin's compound

Crystallisation of Dianin's compound (DC) together with two organic amines (piperazine and piperidine) produces co-crystals of 2:1 DC-piperazine and 1:1 DC-piperidine, respectively. The structures of these adducts contrast sharply with that of the well-known clathrate structure of DC in which organic guests are generally included in ratios of 3:1 or 6:1 DC-guest. © The Royal Society of Chemistry 2009.</p

A mechanochemically synthesised solid solution enables engineering of the sorption properties of a Werner clathrate

Mechanochemical synthesis has been used to obtain two Werner complexes and their solid solution that could not be obtained by conventional “wet” chemistry; remarkably, despite the structural and chemical similarity, the solid solution exhibits sorption properties that differ from those of the pure compounds. © 2012 Royal Society of Chemistry.</p

Carbon dioxide entrapment in an organic molecular host

4-Phenoxyphenol crystallises to yield discrete 60 Å3 cavities that are capable of enclathrating small solvent molecules; the cavities are capped by constricted 6-membered hydrogen-bonded rings and these potential apertures do not appear to facilitate gated porosity when the material is subjected to static CO2 pressure. © 2013 The Royal Society of Chemistry.</p

Co-crystallization of ionic and neutral supramolecular motifs derived from identical components

The concept of co-crystallization usually applies to the coexistence of two or more different types of molecule in the same crystal, but at a higher level of complexity it is possible to define a parallel concept where a crystal is composed of two or more recognizably different supramolecular assemblies. We describe the structure of an adduct formed between Dianin's compound and ethylene diamine. This structure consists of two recognizably different supramolecular assemblies of these components. Furthermore, these two forms have each previously been observed to exist in isolation. Therefore, it is reasonable to make the comparison with conventional co-crystals where two or more compounds that can exist separately form a crystalline adduct (often termed a "molecular complex"). © 2009 American Chemical Society.</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