Nanoporous Metal Phosphonates

Abstract

Nanoporous metal phosphonates make up a growing family of organic–inorganic hybrid solids, which extends the scope of functional materials with potential in adsorption, ion exchange, catalysis, and sensing. Their attributes include thermal stability and the ability to incorporate functional organic and inorganic components accessible to adsorbates. The best established are those based on zirconium, comprising layered solids in which organic groups act as pillars between inorganic zirconium phosphate sheets. The porosity, which can be on the micro‐ or mesoscale, is engineered by design of the organic pillars and their number density and, while not ordered on the long range, can have a narrow distribution. Other pillared layered metal phosphonates are also known. More recent developments have yielded framework metal phosphonates with well‐defined permanent microporosity similar to that observed in zeolites, in the 0.3–1‐nm range, that demonstrate molecular sieving. Currently, the most promising solids of this kind include aluminum methylphosphonates and metal bisphosphonates, which can be described as metal–organic frameworks or MOFs. Another area of smaller, but developing interest is the preparation of metal phosphonates with ordered mesoporosity, in which a wide range of solids with relatively narrow distribution of pore sizes in the 3–15‐nm range is prepared by surfactant‐templated approaches. These have potential in the interaction with large molecules, including proteins.