Directing organic–inorganic hybrid molecular-assemblies of polyoxometalate crown-ether complexes with supramolecular cations

The design of new materials by directing the self-assembly of organic–inorganic hybrid molecular assemblies of polyoxometalate crown-ether complexes with supramolecular cations is reviewed with a particular focus on mixed-valence [PMo<sub>12</sub>O<sub>40</sub>]<sup>4−</sup> building blocks. Structurally configurable supramolecular cations of organic ammonium and crown ethers, i.e. protonated aromatic amines complexed by crown ethers are also outlined. The design principles for the one-electron reduced mixed-valence polyoxomolybdate cluster of [PMo<sub>12</sub>O<sub>40</sub>]<sup>4−</sup> are also deduced. The construction principles behind these assemblies and also the concept of using cluster-based "crowns" to complex the cations to extend the design concept further is discussed, especially in the development of inorganic crowns that could combine the properties of the electronically interesting building block along with the receptor building blocks