Water Content-Controlled Formation and Transformation of Concomitant Pseudopolymorph Coordination Polymers

In Situ Conversion of Ligand to a Coordination Polymer via a Core@Shell Crystal: A Multi-Step Phase-Dependent Structural Transformation

Two pseudopolymorphic 1D coordination polymers of the formulas [Cd(3,3'-pytz)(CH3OH)2(ClO4)2]n (1) and [Cd(3,3'-pytz)(CH3CN)2(ClO4)2]n (2) have been prepared using the electron-deficient 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3'-pytz) ligand and cadmium perchlorate in the chloroform/methanol and chloroform/acetonitrile solvent system, respectively. It was observed that compounds 1 and 2 experienced one-step (CPreagent → CPproduct) single-crystal-to-powder structural transformation to the pure water-coordinated compound [Cd(3,3'-pytz)(H2O)2(ClO4)2]n (3) by absorbing water vapor from air (solid-gas phase transformation). Interestingly, compounds 1, 2, and 3 undergo a different transformation path and show an in situ unique three-step (CPreagent → CPproduct → Ligandintermediate → CPproduct) single-crystal-to-single-crystal (SCSC) structural transformation process through soaking in deionized water (solid-liquid phase transformation). In this fascinating transformation, we report for the first time the direct conversion of a ligand into a coordination polymer by a rare core-shell pathway in a solid-liquid phase transformation. In this process, we obtained compound {[Cd(3,3'-pytz)(H2O)4](3,3'-pytz)2(ClO4)2(H2O)6}n (4) (single-crystal = S, crystal = C, or microcrystal = P) as mixed compounds of core-shell L@4C and 4S or core-shell L@4P and 4P for compounds (1 and 2) and 3, respectively.

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

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) (1a) and Zn(II) (2a) that undergo unprecedented single-crystal to single-crystal (SCSC) transformation toward the corresponding isostructural three-dimensional MOFs of Mn(II) (1b) and Zn(II) (2b). The 2D MOFs 1a and 2a 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 n-propanol. Time-dependent SCSC transformations were studied by in situ X-ray diffraction. Investigations on photodegradation of methyl orange showed that Zn-MOF 2b has higher efficiency than Mn-MOF 1b 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 2b may be attributed to its suitable band-edge position for redox reactions.