Cyclic molecular materials based on [M2O2S2]2+ cores (M = Mo or W)

The purpose of this article is to illustrate how conventional precursors can serve, when used with a drop of imagination, to the synthesis of sophisticated inorganic rings and wheels. The self-condensation of the [M2O2S2](2+) fragments under acido-basic process produces, in the presence or absence of guest species, linear enchainment restricted to discrete cyclic entities. This approach was revealed to be a highly fruitful strategy for developing an extended family of compounds, differing in their nuclearity, size and shape, and the nature of the encapsulated guest molecule. Indeed, the resulting cycles delimit a cationic open cavity, which can be filled by neutral polar molecules such as aquo ligands or anionic molecules such as phosphates, polycarboxylates and even metalates. The flexibility of the rings is at the origin of interesting host-guest properties: the deformation (symmetry) and the adaptation (nuclearity) of the inorganic cycle are directly related to the size and the coordination requirements of the encapsulated substrate. The versatility of the metal coordination, octahedral or square pyramidal, confers dynamic properties to the ring. In the solid state, molecular rings assemble in striking 3-D networks based on direct cation-anion connections. Alkali cations are arranged in pillars or layers for anchoring the anionic rings.