Rare Earth Ion Encapsulated Basket-like {Gd⊂P6MoV2MoVI16O73} Cage as Efficient Electrochemical Sensor and Fluorescent Probe for Cr(VI)

A rare basket-like Gd3+-encapsulated {Gd subset of(P6Mo2Mo16O73)-Mo-V-O-VI} cage has been successfully synthesized with the formula of (H-2 bpp)(6){(GdMo2Mo16O49)-Mo-V-O-VI-(HPO4)(PO4)(5)}(2)center dot 11H(2)O (1) (bpp is 1,3-bi(4-pyridyl)propane). Crystal 1 displays electrochemically reversible redox behavior and fluorescent property, and can serve as a bifunctional electrochemical sensor and fluorescent probe for efficiently detecting chromium (Cr(VI)) in water. As electrochemical sensor, compound 1 showed good electrochemical activity for trace Cr(VI) with a high sensitivity of 0.151 mu A center dot mu M-1 and low detection limit of 0.202 mu M (0.021 ppm). These parameters fully met the WHO standards. When using as fluorescence probe, the detection limit of compound 1 is as low as 8.7 mu M for Cr(VI) in water.