Instantaneous and reversible gelation of organically grafted polyoxometalate complexes with dicarboxylic acids

Abstract

An organically pyridyl-grafted Anderson-type POM complex (TBA–Py–MnMo₆) bearing counterions of tetrabutylammonium (TBA) was found to form supramolecular gels instantaneously through mixing with appropriate dicarboxylic acid additives in acetonitrile. In the gelation process, TBA–Py–MnMo₆ was confirmed to self-assemble into supramolecular polymer chains through unidirectional hydrogen bonding between the pyridyl groups of POMs and the carboxylic groups of dicarboxylic acids, which drove the complexes into one-dimensional fibers. The fibers were demonstrated to further intertwine together through the lateral hydrogen bonding between polymer chains under the support of excess acid, forming three-dimensional networks. The distance between TBA–Py–MnMo₆ units secluded by dicarboxylic acid was proved to be a criterion for the formation of gels, which is related to the TBA density along the supramolecular polymer chains and the solvent–fiber interfacial energy. The gelation behaviour of the hybrid POM complex can be simply controlled through adjusting the length of dicarboxylic acids. More interestingly, the POM hybrid gels exhibited a quick response to organic bases and diacids reversibly.