The release of anthropogenic chemicals and persistent pollutants into waters and soil have resulted in severe threats to public health and the environment. For instance, toxic perfluoroalkyl substances (PFAS) are being found in increasing concentrations near populated areas, and their removal from water is currently a grand challenge. Coordination cages are three-dimensional structures that have shown promise in the capture of toxic chemicals and pollutants.[1] These cages form as thermodynamically favored products from the self-organization of metal ions and organic ligands and feature internal cavities that provide unique nano-environments, differing significantly from bulk conditions. This enables coordination cages to selectively sense, stabilise or transform guest molecules.
Coordination cages with multiple binding sites are particularly intriguing, as they allow for cooperative binding, leading to enhanced selectivity and affinity that single-cavity hosts cannot achieve. Our research focuses on exploring coordination cages based on Pd(II) as hosts for the capture of oxo-anions and perfluoroalkyl pollutants,[2] aiming to address critical environmental challenges caused by these pollutants. For example, we have prepared an interlocked coordination cage with a cation-anion arrangement pattern that enables guest exchange in the cage's two outer pockets. The dimensions of these cavities, as afforded by the interlocked cage motif, result in strong and selective binding of tetrahedral anions including bisulfate.[3] In another project, we are exploring the cooperative aggregation of short and long-chain PFAS within an octahedral coordination cage. Remarkably, this system exhibits strong binding affinity for both short and long-chain PFAS. Furthermore, the incorporation of these coordination cages into silica composites has shown promising performance in water purification applications. These composites effectively remove PFAS, overcoming the limitations of conventional water purification methods that often fail to address these persistent pollutants.