Reversible Single-Crystal-to-Single-Crystal Structural Transformation in a Mixed-Ligand 2D Layered Metal-Organic Framework: Structural Characterization and Sorption Study

A 3D supramolecular network, [Cd(bipy)(C4O4)(H2O)2]·3H2O (1) (bipy = 4,4′-bipyridine and C4O42− = dianion of H2C4O4), constructed by mixed-ligand two-dimensional (2D) metal-organic frameworks (MOFs) has been reported and structurally determined by the single-crystal X-ray diffraction method and characterized by other physicochemical methods. In 1, the C4O42− and bipy both act as bridging ligands connecting the Cd(II) ions to form a 2D layered MOF, which are then extended to a 3D supramolecular network via the mutually parallel and interpenetrating arrangements among the 2D-layered MOFs. Compound 1 shows a two-step dehydration process with weight losses of 11.0% and 7.3%, corresponding to the weight-loss of three guest and two coordinated water molecules, respectively, and exhibits an interesting reversible single-crystal-to-single-crystal (SCSC) structural transformation upon de-hydration and re-hydration for guest water molecules. The SCSC structural transformation have been demonstrated and monitored by single-crystal and X-ray powder diffraction, and thermogravimetic analysis studies.