Synergistic Induction of Solvent and Ligand-Substitution in Single-Crystal to Single-Crystal Transformations toward a MOF with Photocatalytic Dye Degradation

Abstract

External-stimuli responsiveness as found in natural organisms and smart materials is attractive for functional materials scientists who attempt to design and imitate fascinating behavior into their materials. Herein, we report a couple of new solvent-responsive isostructural two-dimensional cationic metal-organic frameworks (MOFs) of Mn(II) (<b>1a</b>) and Zn(II) (<b>2a</b>) that undergo unprecedented single-crystal to single-crystal (SCSC) transformation toward the corresponding isostructural three-dimensional MOFs of Mn(II) (<b>1b</b>) and Zn(II) (<b>2b</b>). The 2D MOFs <b>1a</b> and <b>2a</b> have been effortlessly and rapidly synthesized via the microwave-heating technique. The SCSC transformations are synergistically induced by solvent and ligand-substitution reactions and able to be triggered by water, methanol, ethanol, and <i>n</i>-propanol. Time-dependent SCSC transformations were studied by in situ X-ray diffraction. Investigations on photodegradation of methyl orange showed that Zn-MOF <b>2b</b> has higher efficiency than Mn-MOF <b>1b</b> under UV-C irradiation at 300 min, 94.27%, and 21.91%, respectively. The influence of charge on the dye molecules, heterogeneity of the catalysis, and ^•OH radical-scavenging test was studied. First-principles computations suggest that the high photocatalytic activity of <b>2b</b> may be attributed to its suitable band-edge position for redox reactions.