Encapsulation of polyoxometalates into supramolecular cages based on flexible ligands: Synthesis, structure and properties

• New hybrid compounds have been prepared.
• Keggin-type polyoxometalates as noncoordinating guests wrapped into supramolecular cages based on flexible ligands.
• The supramolecular cages that are formed by the hydrogen bonds (O–H⋯O and N–H⋯O) with organic ligands.

Three Keggin-type polyoxometalates as noncoordinating guests wrapped into supramolecular cages based on flexible ligands, named, [H2L][HL][L]2[PMo12O40]·4H2O (1), [HL]4[SiW12O40] (2) and [HL]2[L]2[PWVWVI11O38(O2)]·4H2O (3) (L = 4-(3-pyridinyloxy)benzoic acid) have been synthesized via hydrothermal conditions and have been characterized by elemental analysis, IR spectroscopy, TG analysis, and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analyses revealed that the Keggin polyanions are wrapped as guests in the supramolecular cages that are formed by the ligands with hydrogen bonds (O–H⋯O and N–H⋯O). Moreover, the fluorescence of the title complexes and the electrochemical properties of 1 have been investigated. In addition, the catalytical properties of compounds have also been investigated.

In compound 1, the [PMo12O40]3− are encapsulated in the supramolecular cages formed by ligands, and the ligands are protonated as H2L and HL. There is no covalent bonds between POMs and ligands. The result shows that the charge of compound 1 is balanced by the ligands, then the whole structure become neutral and stable. The interaction from the intermolecular hydrogen bonds plays an important role in the formation of the whole framework.Figure optionsDownload as PowerPoint slide