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Synthesis and characterization of flexible copper(II) crystals

It was common knowledge that crystalline solids in general, but especially those composed of coordination complexes, are brittle and rigid and tend to break if sufficient amount of mechanical stress is applied. In the past decade, it has been shown otherwise. For many compounds that crystallize as needleshaped crystals, it has been observed that they can respond to the application of mechanical stress either through elastic or plastic deformation. An important structural feature common to many of those flexible crystals was shown to be the existence of a short ‘4 Å’ crystallographic axis. Other intermolecular interactions, such as hydrogen and halogen bonds are also suspected to have a major role in crystal flexibility, so the whole system needs to be carefully engineered. In order to further investigate properties of such crystals, we have synthesized similar coordination polymers. According to literature reports, 1-D cadmium(II) polymers with bridging halide anions as well as 0- D copper(II) compounds showed exceptional elasticity. Here we wanted to combine the two features, and to test the capability of copper(II) halides (bromide and chloride) to form flexible crystals. The ligand, 3-nitropyridine, was selected because of its tendency to form weak hydrogen bonds whose impact on flexibility will be further explored.

coordination polymers ; cooper(II) ; 3-nitropyridine ; flexible crystals

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