Assembly of Supramolecular Polyoxometalate-Cyclodextrin-Based Frameworks Driven by the Chaotropic Effect for Enhanced Proton Conductivity

This study reports on two multicomponent hybrid supramolecular assemblies by integrating polyoxometalates (POMs) and cyclodextrins (CDs) through noncovalent interactions, namely, (NH₄)KH[{FeMo₆(OH)₆O₁₈}(γ-CD)]·26H₂O (denoted as {FeMo₆}(γ-CD), 1) and (NH₄)₃KH[{FeMo₆(OH)₆O₁₈}{Mo₆O₁₉}(γ-CD)₂]·29H₂O (denoted as {Mo₆}{FeMo₆}(γ-CD)₂, 2). 1 represents a two-component open framework built from Anderson-type {FeMo₆} units by interacting with the external surface of γ-CD while 2 could be viewed as a three-component hybrid when inner cavities of (γ-CD)₂ species in 1 are filled by the in situ formed Lindqvist-type {Mo₆O₁₉}^2- anions driven by a chaotropic effect. This pair of hybrid supramolecular assemblies provides a molecular-level platform for exploring the structure-property relationships related to proton conductivity. As expected, the proton conductivity of 2 remains a 3-fold enhancement compared to that of 1, which may be arisen from the increasing numbers of "proton-carrier" molecules due to the introduction of {Mo₆O₁₉}^2- guest within the macrocyclic host matrix. This work paves the way for engineering multifunctional POM-CD-based supramolecular frameworks featuring tailor-made properties controlled by inorganic POM entities through a chaotropic effect.