Four Dawson POM-based inorganic-organic supramolecular compounds for proton conduction, electrochemical and photocatalytic activity

Four new inorganic-organic hybrid compounds based on the Wells-Dawson polyoxometalate, namely. [Ni(H2bibb)2(H2O)3(α-P2W18O62)]·7H2O (1), [Co(H2bibb)2(H2O)3(α-P2W18O62)]·10H2O (2), [Cu(H2bibb)2(H2O)3(α-P2W18O62)]·10.5H2O (3) and [Zn(Hbibb)2(H2O)](α-P2W18O62)(H2bibb)·5H2O (4) (bibb ​= ​1,3-bis(1-imidazolyl)-5-(2-benzimidazolyl)benzene) have been synthesized by hydrothermal method. Compounds 1, 2 and 3 have similar configurations, of which the mononuclear units are all connected into a 2D supramolecular layer by hydrogen bonding and π … π stacking interactions, and then further extended into a 3D supramolecular structure. For compound 4, the binuclear {Zn2(Hbibb)4} units are connected to form a 3D supramolecular network through hydrogen bonding and π … π stacking interactions. Alternating-current impedance measurement suggests that the highest proton conductivity of compound 3 is up to 2.52 ​× ​10−4 ​S ​cm−1 (85 ​°C, 98% RH). The photocatalytic degradation of RhB by these compounds indicates that the dye degradation rate shown by catalyst 1 is the highest, reaching 67.14%. In addition, the electrochemical properties of these compounds are also investigated.