Redox-Responsive Host–Guest Association between γ-Cyclodextrin and Mixed-Metal Keggin-Type Polyoxometalates Article Swipe
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· 2021
· Open Access
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· DOI: https://doi.org/10.1021/acs.inorgchem.1c00724
· OA: W3157219091
The complexation of Keggin-type polyoxometalates (POMs) with γ-cyclodextrin (γ-CD) leads to supramolecular inclusion assemblies in aqueous solution driven by a chaotropic effect. The strength of the interaction between γ-CD and oxidized or one-electron reduced POMs in a series of molybdenum and vanadium monosubstituted phospho- and silico-tungstates, [XW<sub>11</sub>MO<sub>40</sub>]<sup><i>n</i>-</sup> Keggin-type anions where X = P or Si and M = Mo<sup>V/VI</sup> or V<sup>IV/V</sup>, has been evaluated by isothermal titration calorimetry (ITC), NMR spectroscopy, and cyclic voltammetry. Such a study reveals that the host-guest binding constant <i>K</i><sub>1:1</sub> increases strongly with the decrease of the global ionic charge of the POM unit. There is an almost one magnitude order of variation in <i>K</i><sub>1:1</sub> per charge unit, where <i>K</i><sub>1:1</sub> falls down from about 10<sup>5</sup> M<sup>-1</sup> to values close to zero as ionic charge varies from 3- to 6-. Such POMs with molybdenum and vanadium addenda offer the possibility of tuning the host-guest association strength by the simple addition/removal of one electron to POMs, opening a new avenue for the design of smart materials through redox stimuli.
