Rheoreversible Metallogels Derived from Coordination Polymers

A series of mixed-ligand-based Cd^II /Co^II coordination polymers (CPs) that were derived from two bis(pyridyl)-bis(amide) ligands, 4,4'-oxybis(N-(pyridin-3-yl)benzamide) (LP) and 4,4'-oxybis(N-(pyridin-4-yl)benzamide) (LP1), and a variety of dicarboxylates isophthalates, terephthalates, 1,2-carboxytranscinamates, and 1,3- and 1,4-phenylene dicarboxylates were synthesized based on a rationale that they would occlude solvate guests inside their crystal lattice, thereby rendering these CPs suitable as metallogelators. The CPs were characterized by using single-crystal X-ray diffraction, elemental analysis, powder X-ray diffraction (PXRD), FTIR spectroscopy, and thermogravimetric analysis (TGA). Structural analyses revealed that the majority of the CPs were lattice-occluded molecular solids, which provided us with an opportunity to study their gelation behavior. We observed that, out of eight CPs that were tested, seven were able to produce metallogels. A thorough study of the rheological behavior of the metallogels was performed and CPG1, CPG2, CPG4, and CPG5 were found to exhibit rheoreversible behavior, which was further confirmed by rheological experiments. Interestingly, ligand LP was found to form an aqueous gel, which was exploited to produce silver nanoparticles.