A series of cyanoacetato copper(II) coordination polymers with various N,N'-ditopic spacers: structural diversity, supramolecular robustness, and magnetic properties

Five novel copper(II) coordination polymers containing cyanoacetate (cna) anion with various N,N′-ditopic spacers [Cu(cna)2(pyz)]n (1), [Cu(cna)2(bpy)(H2O)2]n (2), [Cu(cna)2(dpe)]n (3), [Cu(cna)2(dpe)]n(H2O)n (4), and [Cu(cna)2(bpa)]n (5) (when pyz = pyrazine, bpy = 4,4′-bipyridyl, dpe = 1,2-di(4-pyridyl)ethylene, and bpa = 1,2-di(4-pyridyl)ethane) were structurally and spectroscopically characterized. Compound 1 shows a two-dimensional (2D) sheet structure constructed from μ2-1,3(syn,anti) coordinative mode of cyanoacetate and μ2-pyz linking adjacent Cu(II) centers. Compound 2 exhibits a one-dimensional (1D) polymeric chain which is formed by μ2-bpy bridging between [Cu(cna)2(H2O)2] units, whereas compounds 3–5 reveal 1D ladder-like structures which are built from double-μ2-dpe/bpa spacers connecting neighboring Cu(II) cyanoacetate dimers. Weak interactions such as hydrogen bonding and N···π and/or C–H···π interactions join the adjacent layers of 1 or polymeric chains of 2–5 to stabilize overall supramolecular networks. The thermal stabilities of 1–5 were investigated. Interestingly, compound 2 reveals a robust supramolecular framework constructed by 1D polymeric chains during thermal dehydration and rehydration processes, which has been further verified by spectroscopic techniques, elemental analyses, thermogravimetric analysis, and X-ray powder diffraction. Moreover, this behavior is not observed in the isomorphous series containing Co(II) and Ni(II) ions. The magnetic properties of 1 and 3 exhibit very weak antiferromagnetic interactions between Cu(II) centers.