Complexation of polyoxometalates with cyclodextrins.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Inorganic Chemistry

Background:

• Complexation of hydrophilic guests within hydrophobic hosts is typically challenging.
• Polyoxometalates (POMs) are versatile inorganic clusters with diverse applications.
• Cyclodextrins (CDs) are well-established host molecules in supramolecular chemistry.

Purpose of the Study:

• To investigate the complexation of a polyoxometalate ([PMo12O40](3-)) with gamma- and beta-cyclodextrins (CDs).
• To characterize the structure and properties of the resulting organic-inorganic hybrid complexes.
• To explore the potential of host-guest chemistry for functionalizing POMs.

Main Methods:

• Synthesis of 2:1 cyclodextrin-POM complexes ([La(H2O)9]{[PMo12O40]⊂[γ-CD]2} and [La(H2O)9] {[PMo12O40]⊂[β-CD]2}).
• Structural analysis using single-crystal X-ray diffraction.
• Solution behavior investigation via NMR spectroscopy, X-ray scattering, and mass spectrometry.
• Electrochemical studies to assess redox properties.

Main Results:

• Formation of two stable 2:1 organic-inorganic hybrid complexes in the solid state.
• Single-crystal X-ray diffraction revealed a sandwich-like structure with POM encapsulated by two CDs via C-H···O═Mo interactions.
• Complexes form 1D columnar superstructures in the solid state through O-H···O interactions.
• Evidence of nanoconfinement effects and slow color changes in aqueous solution.
• Encapsulated POMs largely retain their redox properties in solution.

Conclusions:

• Demonstrated successful complexation of a hydrophilic POM within hydrophobic CDs, challenging previous assumptions.
• The supramolecular complementarity enables the formation of well-defined hybrid materials with potential for functionalization.
• Host-guest chemistry offers a mild approach for modifying POM properties and applications.