Capped Keggin Type Polyoxometalate-Based Inorganic-Organic Hybrids Involving In Situ Ligand Transformation as Supercapacitors and Efficient Electrochemical Sensors for Detecting Cr(VI)

To construct polyoxometalate-based complexes as electrode materials for supercapacitors and electrochemical sensors, we intentionally used in situ ligand transformation during the reaction. Two complexes based on polyoxometalates capped by zinc ions, H{Zn-4(DIBA)(4)[(DIBA)(HPO2)](2)(alpha-(PMo8Mo4O40Zn2)-Mo-VI-O-V)} (1) and [epsilon-(PMo8Mo4O37)-Mo-V-O-VI(OH)(3)Zn-4(HDBIBA)(2)]center dot 6H(2)O (2) [DIBA = 3,5-di(1H-imidazol-1-yl)benzoic acid, and DBIBA = 3,5-bis(1H-benzoimidazol-1-yl)benzoic acid], have been prepared successfully. The DIBA and DBIBA ligands were generated in situ from initial materials 3,5-di(1H-imidazol-1-yl)benzonitrile and 3,5-di(1H-benzoimidazol-1-yl)benzonitrile. The three-dimensional structure of 1 consisted of two-dimensional interpenetrating layers and polyoxometalate-based chains composed of bicapped alpha-PMo12Zn2 polyoxoanions and phosphite-modified DIBA ligands. In 2, a kind of tetracapped epsilon-PMo12Zn4 polyoxoanion exists, which was further linked by DBIBA ligands into a one-dimensional chain. Two complexes could be employed as not only electrode materials for supercapacitors with specific capacitances of 171.17 F g(-1) for 1 and 146.77 F g(-1) for 2 at 0.5 A g(-1) but also efficient electrochemical sensors for detecting Cr(VI) with excellent limits of detection of 0.026 mu M for 1 and 0.035 mu M for 2, which represents a hopeful approach for exploiting polyoxometalate-based complexes as supercapacitor and electrochemical sensor materials.