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.