High-pressure reversibility in a plastically flexible coordination polymer crystal

Single crystals which exhibit mechanical flexibility are promising materials for advanced technological applications. Before such materials can be used, a detailed understanding of the mechanisms of bending is needed. Using single crystal X-ray diffraction and microfocus Raman spectroscopy, we study in atomic detail the high-pressure response of the plastically flexible coordination polymer [Zn(μ-Cl) 2 (3,5-dichloropyridine) 2 ] n ( 1 ). Contradictory to three-point bending, quasi-hydrostatic compression of ( 1 ) is completely reversible, even following compression to over 9 GPa. A structural phase transition is observed at ca . 5 GPa. DFT calculations show this transition to result from the pressure-induced softening of low-frequency vibrations. This phase transition is not observed during three-point-bending. Microfocus synchrotron X-ray diffraction revealed that bending yields significant mosaicity, as opposed to compression. Hence, our studies indicate of overall disparate mechanical responses of bulk flexibility and quasi-hydrostatic compression within the same crystal lattice. We suspect this to be a general feature of plastically bendable materials. Mechanically flexible single crystals are promising materials for advanced technological applications. Here, the authors study the high pressure response of a plastically flexible coordination polymer and provide indication of an overall disparate mechanical response of bulk flexibility and quasi-hydrostatic compression within the same crystal lattice.