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Mechanical properties of copper(II) and cadmium(II) halides equipped with 3-nitropyridine ligands

For a long time crystals were considered to be brittle and rigid substances that readily break when external mechanical force is applied. Recent research has shown that crystals can also exhibit elastic and plastic deformations under mechanical force. Our research on 1D cadmium(II) halide coordination polymers equipped with halogen substituted pyrazine ligands has shown that the obtained crystals can deform elastically and revert to their original shape as mechanical force is applied and released.[1] It was also shown that intermolecular interactions could indeed play a crucial role in defining the mechanical properties of these compounds. Halogen bonds found in this class of compounds are classified as relatively weak and comparable to weak hydrogen bonds.[2] Therefore, if the organic ligands are replaced by similar small and rigid ones bearing weak hydrogen bond donors, crystals should also be able to produce similar mechanical output. To test this hypothesis and further explore the effects of intermolecular interactions on mechanical properties of prepared crystals we opted to use 3- nitropyiridne ligands as weak hydrogen bond donors and to further extend our research to copper(II) halides since they also form 1D coordination polymers. Coordination polymers of Cd(II) and Cu(II) halides (Cl, Br) with 3-nitropyridine ligands were prepared using the liquid diffusion method. All four possible coordination polymers were obtained, and their crystal structures were determined. Their mechanical properties were studied using a modified three point bending method and corelated with crystal structural features.

crystals ; mechanical flexibility ; elastic ; plastic ; cadmium ; copper

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