Structure and reversible crystal-to-crystal transformations of a zinc(II) coordination polymer constructed from an imide-based dicarboxylic acid.

An imide-based O-donor ligand, 4-carboxyphenyl-1,3-dioxoisoindoline-5-carboxylic acid (H 2 In-4-ba), and one Zn(II) coordination polymer, [Zn(In-4-ba)(py) 2 ] n (1 , py ​= ​pyridine), have been synthesized. Single-crystal X-ray diffraction indicates that 1 has a quasi-3 1 helical chain structure, which shows one-dimensional to two-dimensional (1D → 2D) extension to be a homochiral layer of consecutively interweaving poly-helices with the same helicity. Coexistence of such homochiral layers in opposite chirality makes individual crystal of 1 to be in a racemic manner. Thermogravimetric (TG) analysis indicated that 1 shows high thermal stability approaching 440 ​°C. Thermal activation of 1 gives a desolvated phase, [Zn(In-4-ba)] n (1′), as supported by TG trace. Of particular note, reversible crystal-to-crystal transformations between solvated 1 and desolvated 1′ have been achieved upon decoordination and recoordination of the py ligands, as evidenced by XRPD patterns, IR spectra, and TG diagrams. The photoluminescence properties of as-synthesized 1 , desolvated 1′ , and resolvated 1′ /py have also been studied. All of them exhibit an emission band centered at 486, 492, and 486 ​nm, respectively, which is originated from the ligand-centered charge transfer. Further, the emission intensity of 1′ is weaker than that of 1 and 1′ /py, implying the influence of coordinated py ligands and/or structure regulation on photoluminescence. A solvated zinc(II) coordination polymer showing quasi-3 1 helical chain structure and its desolvated phase have exhibited reversible crystal-to-crystal transformations upon solvent decoordination and recoordination. [Display omitted] • Zn(II) coordination polymer 1 has a quasi-3 1 helical chain structure. • Zn(II) coordination polymer 1 shows 1D.→ 2D homochiral layer of poly-helices. • Zn(II) coordination polymer 1 is high thermally stable approaching 440 ​°C. • Zn(II) coordination polymer 1 exhibits ligand-centered fluorescence. • Solvent-induced reversible crystal-to-crystal transformations have been achieved. [ABSTRACT FROM AUTHOR]