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(L-salpyca)(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(L-salpyca)](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 L-salpyca ligand and the coordination geometry around the Zn(II) center.