Reversible Single-Crystal to Single-Crystal Transformations of a Zn(II)–Salicyaldimine Coordination Polymer Accompanying Changes in Coordination Sphere and Network Dimensionality upon Dehydration and Rehydration

A fluorescent Zn­(II)–salicyaldimine coordination polymer, [Zn­(Lsalpyca)­(H2O)]n (1; H2Lsalpyca = 4-hydroxy-3-(((pyridin-2-yl)­methylimino)­methyl)­benzoic acid), showing a one-dimensional (1D) zigzag chain structure has been hydro­(solvo)­thermally synthesized. Removal of coordination water molecules in 1 by thermal dehydration gives rise to the dehydration product [Zn­(Lsalpyca)]n (1′), which has a dizinc-based two-dimensional (2D) gridlike (4,4)-layer structure. X-ray powder diffraction (XRPD) patterns, thermogravimetric (TG) analyses, and infrared (IR) spectra all clearly indicate that the structure of 1 is quite flexible as a result of a reversible 1D–2D single-crystal to single-crystal (SCSC) transformation upon removal and rebinding of coordination water molecules, which accompanies changes in coordination sphere and network dimensionality. Additionally, Zn­(II)–salicyaldimine polymers 1 and 1′ exhibit different solid-state photoluminescences at 458 and 480 nm, respectively. This is reasonably attributed to the close-packing effect and/or the influences of the differences on the conformation and the coordination mode of the Lsalpyca ligand and the coordination geometry around the Zn­(II) center.

一种荧光性Zn(II)-水杨亚胺配位聚合物[Zn(Lsalpyca)(H₂O)]ₙ（编号1；其中H₂Lsalpyca代表4-羟基-3-[(吡啶-2-基)甲亚胺基]甲基苯甲酸），通过水热（溶剂热）法合成，其结构呈现一维（1D）之字形链状结构。通过热脱除工艺去除化合物1中的配位水分子，可得到脱水产物[Zn(Lsalpyca)]ₙ（编号1′），该产物具有基于双核锌的二维（2D）网格状(4,4)-层状结构。X射线粉末衍射（X-ray powder diffraction, XRPD）图谱、热重（thermogravimetric, TG）分析以及红外（infrared, IR）光谱的测试结果均明确表明，化合物1的结构具有显著柔性：在配位水分子脱除与重新结合的过程中，可发生可逆的1D-2D单晶到单晶（single-crystal to single-crystal, SCSC）转变，该转变同时伴随配位环境与网络维度的变化。此外，Zn(II)-水杨亚胺聚合物1与1′分别在458 nm与480 nm波长处表现出不同的固态光致发光特性。该现象可合理归因于配体Lsalpyca的构象与配位模式差异、Zn(II)中心配位几何构型的变化，以及紧密堆积效应的共同影响。