Chapter 5 - Polyoxometalate-based host–guest framework materials

Abstract

The combination of polyoxometalates (POMs) with metal-organic frameworks (MOFs) was anticipated to merge POMs' qualities into MOFs' to create materials with special structures and properties involving high stability in water in comparison with isolated POMs, which are highly unstable in water, particularly in strong acidic/basic aqueous media. In general, known POM-based MOF has been divided into two types: (a) POM only is a secondary building unit (SBU) of MOF's framework and (b) POM only is a guest to forms a host–guest relationship, which frequently shows exclusive assets ascribed to the gentle interactions between host and guest, for example, MOFs, hydrogen bonding, anion-π interactions, etc. Nevertheless, to the best of our knowledge, those with POM behaving as both SBU and guest stay on unknown to this point. Logically, as anionic clusters with oxygen-rich surfaces, POMs have a preference to bond metal cations instead of neutral/negative organic ligands. Thus, the synthesis of POM-based MOF with POM as the node is considered a puzzling topic, let alone bi-POM-based host–guest MOFs.