Polyoxometalate, Cationic Cluster and γ-Cyclodextrin. From Primary Interactions to Supramolecular Hybrid Materials.

Moussawi MA , Leclerc-Laronze N , Floquet S , Abramov PA , Sokolov MN , Cordier S , Ponchel A , Monflier E , Bricout H , Landy D , Haouas M , Marrot J , Cadot E
Journal of the American Chemical Society
Herein, we report on a three-component supramolecular hybrid system built from specific recognition processes involving a Dawson type polyoxometalate [P2W18O62](6-,) a cationic electron-rich cluster {[Ta6Br12(H6O)6]@2CD}(2+) and γ-cyclodextrin. Investigations of such a class of materials have been conducted using bottom-up approach by studying the specific interactions between -CD and both types of inorganic units. Their ability to interact has been investigated in the solid state by single-crystal X-ray diffraction and in solution using multinuclear NMR methods (including DOSY, EXSY and COSY), ESI-mass and UV-vis spectroscopies, electrochemistry and ITC experiments. Single-crystal X-Ray diffraction analysis reveals that POM : γ-CD constitutes a highly versatile system which gives aggregates with the 1:1, 1:2 and 1:3 stoichiometry. Surprisingly, these arrangements exhibit common feature wherein the γ-CD moiety interact with the Dawson-type polyoxometalates through its primary face. We present also the first structural model involving octahedral-type metallic cluster with γ-CD. X-ray diffraction study reveals that the cationic {[Ta6Br12(H6O)6]@2CD}(2+) ion is closely embedded within two -CD units to give a supramolecular ditopic cation, suitable to be used as linker within extended structure. Solution study demonstrates clearly that pre-associations exist in solution for which binding constants and thermodynamic parameters have been determined, giving preliminary arguments about the chaotropic nature of the inorganic ions. Finally, both building blocks i.e. the ditopic supramolecular cation {[Ta6Br12(H6O)6]@2CD}(2+) and the Dawson-type anion react together to give three-component well-ordered hybrid material derived either as supramolecular hydrogel or single-crystals. Solid state structure shows an unprecedented helicoidal tubular chain resulting from the periodic alternation of POM and supramolecular cation, featured by short hydrogen bonding contact between electron-poor POM and electron-rich cluster. The 1D tubular ionic polymer observed in the single-crystals should allow understanding the long-range ordering observed within the hydrogel hybrid material. The supramolecular chemical complementarities between the γ-CD- based ditopic cation and polyoxometalate open a wide scope for the design of hybrid materials that cumulate synergistic functionalities.

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