engleski

Engineering mechanical flexibility in crystalline coordination polymers and their two-component systems

Crystal engineering of molecular solids constantly progresses in the last 50 years, but unfortunately, going from molecular to supramolecular structure, and property engineering is still not a straightforward task.1, 2 Recently, it was observed that some molecular crystals can display newly described property that is characteristic of soft matter, but highly unusual for crystalline solids – mechanical responsiveness and mobility when they are subjected to different kinds of external stimuli.3-8 Such molecular crystals have attracted attention of wider scientific community, and research resulted with a number of reports on flexible organic, 4-6 and only a few metal-organic compounds.7, 8 Unfortunately, the structural features that lead to such responsive crystalline materials are not yet fully understood, and if we want to be in a position to deliberately design and deliver such materials a deeper understanding of relations between molecular structure and intermolecular interactions (i.e. how small and controllable changes in molecular structure can influence intermolecular interactions and therefore mechanical properties) is still needed. Recently, we published the first reported on a class of coordination polymers of cadmium(II) with halopyrazine ligands that give highly elastic response upon application of external mechanical stress, which in turn can even be fine-tuned by implying slight structural changes.8 In order to further investigate the link between the crystal structure and mechanical properties, we combined those coordination polymers with several organic compounds in a series of two-component systems with intention to examine the impact of (i) the distances, and (ii) strength of the supramolecular connection between the 1-D building units on their responses to external mechanical stimuli. Needle- shaped crystals of the examined two-component systems showed highly unexpected flexible responses.

crystal engineering, coordination polymers, crystal flexibility

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