Nanoconfinement of polyoxometalates in cyclodextrin: computational inspections of the binding affinity and experimental demonstrations of reactivity modulation

Abstract

Chaotropic polyoxometalates (POMs) form robust host–guest complexes with γ-cyclodextrin (γ-CD), offering promising applications in catalysis, electrochemical energy storage, and nanotechnology. In this article, we provide the first computational insights on the supramolecular binding mechanisms using density-functional theory and classical molecular dynamics simulations. Focusing on the encapsulation of archetypal Keggin-type POMs (PW₁₂O₄₀³⁻, SiW₁₂O₄₀⁴⁻ and BW₁₂O₄₀⁵⁻), our findings reveal that the lowest-charged POM, namely PW₁₂O₄₀³⁻ spontaneously confines within the wider rim of γ-CD, but BW₁₂O₄₀⁵⁻ does not exhibit this behaviour. This striking affinity for the hydrophobic pocket of γ-CD originates from the structural characteristics of water molecules surrounding PW₁₂O₄₀³⁻. Moreover, through validation using ³¹P NMR spectroscopy, we demonstrate that this nanoconfinement regulates drastically the POM reactivity, including its capability to undergo electron transfer and intermolecular metalate Mo/W exchanges. Finally, we exploit this nanoconfinement strategy to isolate the elusive mixed addenda POM PW₁₁MoO₄₀³⁻.