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Mechanically induced flexibility of copper(II) coordination polymers crystals

It has been noted that inducing mechanical force on crystals could result in distinctive responses: brittle crystals will crack during the application of mechanical force while flexible crystals will bend plastically or elastically in response to mechanical stress. [1] Prompted by recently reported bendability of crystalline coordination compounds [2, 3] we decided to investigate analogous metal-organic systems of copper(II) equipped with pyridine derivatives as ligands, namely [CuCl2(4-methylpyridine)2]n (1) and [CuBr2(4-methylpyridine)2]n (2). Layering technique was employed for synthesis and crystallization, and it was observed that ethanol and isopropanol produce single crystals of the required quality for further examination. The resulting compounds were characterized by powder X-ray diffraction (PXRD) and molecular and crystal structures were determined using single-crystal X- ray diffraction (SCXRD). Needle-like crystals were isolated and subjected to bending experiments in order to study their mechanical properties. The type of mechanical response was examined using the modified three-point bending method and it was determined that compound 2 showed plastic behavior, unlike compound 1 for which elastic responsiveness was observed, hence the degree of elasticity was calculated.

mechanically induced flexibility, crystals, copper(II)

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