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A Series of Cyanoacetato Copper(II) Coordination Polymers with Various <i>N</i>,<i>N</i>′‑Ditopic Spacers: Structural Diversity, Supramolecular Robustness, and Magnetic Properties
Five
novel copperÂ(II) coordination polymers containing cyanoacetate
(cna) anion with various <i>N</i>,<i>N</i>′-ditopic
spacers [CuÂ(cna)<sub>2</sub>Â(pyz)]<sub><i>n</i></sub> (<b>1</b>), [CuÂ(cna)<sub>2</sub>Â(bpy)Â(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub> (<b>2</b>), [CuÂ(cna)<sub>2</sub>Â(dpe)]<sub><i>n</i></sub> (<b>3</b>),
[CuÂ(cna)<sub>2</sub>Â(dpe)]<sub><i>n</i></sub>Â(H<sub>2</sub>O)<sub><i>n</i></sub> (<b>4</b>), and [CuÂ(cna)<sub>2</sub>Â(bpa)]<sub><i>n</i></sub> (<b>5</b>)
(when pyz = pyrazine, bpy = 4,4′-bipyridyl, dpe = 1,2-diÂ(4-pyridyl)Âethylene,
and bpa = 1,2-diÂ(4-pyridyl)Âethane) were structurally and spectroscopically
characterized. Compound <b>1</b> shows a two-dimensional (2D)
sheet structure constructed from μ<sub>2</sub>-1,3Â(<i>syn,anti</i>) coordinative mode of cyanoacetate and μ<sub>2</sub>-pyz linking
adjacent CuÂ(II) centers. Compound <b>2</b> exhibits a one-dimensional
(1D) polymeric chain which is formed by μ<sub>2</sub>-bpy bridging
between [CuÂ(cna)<sub>2</sub>Â(H<sub>2</sub>O)<sub>2</sub>] units,
whereas compounds <b>3</b>–<b>5</b> reveal 1D ladder-like
structures which are built from double-μ<sub>2</sub>-dpe/bpa
spacers connecting neighboring CuÂ(II) cyanoacetate dimers. Weak interactions
such as hydrogen bonding and N<i>···π</i> and/or C–H<i>···π</i> interactions
join the adjacent layers of <b>1</b> or polymeric chains of <b>2</b>–<b>5</b> to stabilize overall supramolecular
networks. The thermal stabilities of <b>1</b>–<b>5</b> were investigated. Interestingly, compound <b>2</b> 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
CoÂ(II) and NiÂ(II) ions. The magnetic properties of <b>1</b> and <b>3</b> exhibit very weak antiferromagnetic interactions between
CuÂ(II) centers