Three New Difunctional Electrocatalysts Built from Polyoxometalates and Cu–Tpy Units: Experimental and Theoretical Study

Three new organic–inorganic compounds based on polyoxometalates, [(CuCltpy)2(Cu2Cl2(tpy)2)­(α-SiW12O40)]·5H2O (1), [Cu4(tpy)4(H2O)4(α-P2W18O62)]·4H2O (2), and [Cu­(tpy)­(Mo3O10)]·H2O (3) (tpy = 4′-(pyrrol-3-yl)-2,2′:6′,2″-terpyridine), were facilely isolated by hydrothermal technique. X-ray diffraction analysis shows that compound 1 with three-dimensional (3D) supramolecular structure is featured by α-SiW12 clusters, {Cu2Cl2/tpy} dimers, and {CuCl/tpy} monomers. Compound 2 with zero-dimensional (0D) discrete structure is constructed from α-P2W18 clusters and four Cu/tpy units. The one-dimensional (1D) infinite chain of 3 is stemmed from [Mo3O10]2– units and Cu/tpy motifs. Furthermore, we explored the bifunctional electrocatalytic activities of these three compounds for reduction and oxidation. The results show that the [Mo3O10]2–-type hybrid displays better difunctional electrocatalytic activities than heteropolyacids toward both reduction and oxidation. Significantly, the molecular electrostatic potential and the frontier molecular orbital were achieved by density functional theory calculations to analyze the electronic structure of three compounds. The natural bond orbital analysis was also carried out to interpret electron charge distribution.