Supramolecular Assembly And Performance Studies Based On Covalently Modified Anderson-type Polyoxometalates

Polyoxometalates(POMs)are a class of polynuclear metal-oxygen cluster compounds composed of high-valence former transition metals and oxygen atoms.Due to their unique structures and rich physical and chemical properties,POMs have been widely used in research fields of catalysis,energy,medicine,etc.Supramolecular self-assembly based on POMs and organic macrocyclic compounds is an effective method to expand the structure and function of POMs.However,up to now the POM-based supramolecular self-assemblies are mainly constructed from pure inorganic POM clusters and the self-assembly products are lack of controllability.To overcome this problem,we introduce covalently modified Anderson-type POMs into the supramolecular self-assembly to guide the assembly of POMs and macrocyclic molecules.As a consequence,a series of POM-based supramolecular assembly single crystals with controlled molecular composition and structures have been obtained via cationic modulation and covalent modification of POMs.First,Anderson-type POMs symmetrically modified by aniline groups have been obtained via stepwise modification method.Cation exchange of the TBA cations of the obtained Anderson hybrid into sodium and potassium ions leads to supramolecular single crystals after complexation with 18-crown-6 ethers.The supramolecular assemblies show a 1:1 and 1:2stoichiometry of POM to crown ether for sodium and potassium cations,respectively.Protonation of the aniline groups leads to supramolecular single crystals with a 1:3 stoichiometry of POM to 18-crown-6.All the three products have been investigated in solution by NMR spectroscopy and in the solid state using single-crystal X-ray diffraction,etc.The electrochemical performances have also been investigated by cyclic voltammetry.Secondly,the supramolecular self-assembly of γ-CD and Andersontype POMs symmetrically modified with aniline and nitrobenzene groups have been investigated.It is found that the complexation of γ-CD and aniline modified Anderson POM leads to supramolecular assembly with a 1:2stoichiometry of POM to CD.While the complexation of γ-CD and nitrobenzene modified Anderson clusters leads to supramolecular single crystals with a 1:1 and 1:2 stoichiometry under different conditions.The self-assembled products have been investigated in solution by NMR spectroscopy,and ESI-TOF-MS,and in the solid state using single-crystal X-ray diffraction,etc.The supramolecular interactions between POM and CD have been investigated by NMR titration,2D NOESY NMR and isothermal calorimetry(ITC).The aforementioned supramolecular assembly based on symmetrically modified Anderson-type POMs and macrocyclic molecules such as crown ethers and CDs not only expands the structural compositions of POMs,but also lays the foundation for the application in the field of functional materials.This work provides a new idea to guide the orderly and controlled assembly of covalently modified POMs.