Supramolecular assembly of covalently modified Anderson-type polyoxometalates and crown ethers towards pseudo-rotaxane structures

The supramolecular assembly of a series of covalently modified Anderson-type polyoxometalates (POMs) and 18-crown-6 ethers has been investigated for the first time. Seven new POM-crown ether complexes are prepared by varying the countercations and the modification modes of the Anderson clusters, and fully characterized by single-crystal X-ray diffraction, ESI-TOF-MS, ¹H-NMR etc. It is demonstrated that alkali metal cations residing in the cavity of crown ethers are served as super-cations to bind the POM hybrids, thereby generating supramolecular assemblies with different architectures and compositions. More interestingly, five out of the seven POM-crown ether complexes show novel pseudo-rotaxane structures, which are obtained by changing the modification modes of the Anderson clusters from symmetric to asymmetric ones. These pseudo-rotaxanes have not been reported previously, and are considered as an effective pathway to construct POM-based supramolecular architectures with complementary structural and chemical properties.