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A novel triptycene-based polymer of intrinsic microporosity (Trip-PIM) displays enhanced surface area (1065 m2 g(-1)) and reversibly adsorbs 1.65% hydrogen by mass at 1 bar/77 K and 2.71% at 10 bar/77 K.

We report the synthesis and properties of network polymers of intrinsic microporosity (network−PIMs) derived from triptycene monomers that possess alkyl groups attached to their bridgehead positions. Gas adsorption can be controlled by the length and branching of the alkyl chains so that the apparent BET surface area of the materials can be tuned within the range 618−1760 m2 g−1. Shorter (e.g., methyl) or branched (e.g., isopropyl) alkyl chains provide the materials of greatest microporosity, whereas longer alkyl chains appear to block the microporosity created by the rigid organic framework. The enhanced microporosity, in comparison to other PIMs, originates from the macromolecular shape of the framework, as dictated by the triptycene units, which helps to reduce intermolecular contact between the extended planar struts of the rigid framework and thus reduces the efficiency of packing within the solid. The hydrogen adsorption capacities of the triptycene-based PIMs with either methyl or isopropyl substituents are among the highest for purely organic materials at low or moderate presures (1.83% by mass at 1 bar/77K; 3.4% by mass at 18 bar/77 K). The impressive hydrogen adsorption capacity of these materials is related to a high concentration of subnanometre micropores, as verified by Horvath−Kawazoe analysis of low-pressure nitrogen adsorption data.

Many crystalline solids cannot be prepared as single crystals of sufficient size and/or quality for structure determination to be carried out using single crystal X-ray diffraction techniques. In such cases, when only polycrystalline powders of a material are available, it is necessary instead to tackle structure determination using powder X-ray diffraction. This article highlights recent developments in the opportunities for determining crystal structures directly from powder diffraction data, focusing on the case of molecular solids and giving particular attention to the most challenging stage of the structure determination process, namely the structure solution stage. In particular, the direct-space strategy for structure solution is highlighted, as this approach has opened up new opportunities for the structure determination of molecular solids. The article gives an overview of the current state-of-the-art in structure determination of molecular solids from powder diffraction data. Relevant fundamental aspects of the techniques in this field are described, and examples are given to highlight the application of these techniques to determine crystal structures of molecular materials.

Application of a technique developed for in situ solid-state (13)C NMR studies of crystallization processes reveals direct evidence that crystallization of glycine from a methanol/water solution involves the initial transient formation of the beta polymorph, which then undergoes a solution-mediated polymorphic transformation to yield the more stable alpha polymorph.