Two 2D Polyoxometalate‐Based Metal‐Organic Complexes Constructed from a New Flexible N‐Donor Ligand with High Capacitance Performances and Low Detection Limits of Cr(VI)

Abstract By designing and using a new flexible bis(pyrimidine)‐bis(amide) ligand H 2 L [H 2 L=N,N′‐bis(4‐pyrimidinecarboxamido)‐1,3‐propane], two new polyoxometalate (POM)‐based metal‐organic complexes (MOCs), H 3 [Cu 2 (L) 2 (PMo 12 O 40 )] ( 1 ) and [Cu 2 (H 2 L) 2 (β‐Mo 8 O 26 )] ( 2 ), were synthesized under solvothermal and hydrothermal conditions, respectively. In complexes 1 and 2 , metal‐organic units and POM anions are linked together to form two distinct 2D structures. The [PMo 12 O 40 ] 3− (PMo 12 ) anions were used as μ 4 ‐bridging ligands in complex 1 and linked the 1D [Cu(L)] n metal‐organic chains to form a 2D layered structure. The [β‐Mo 8 O 26 ] 4− (Mo 8 ) anions adopted two diverse coordination modes in complex 2 and connected the 1D [Cu(H 2 L)] n 2n+ metal‐organic chains to generate a 2D grid structure. Complexes 1 – 2 can serve as electrode materials of supercapacitor and show large specific capacitances, up to 1065 and 956 F g −1 at current density of 2 A g −1 , respectively, which surpass the parent POM and most of the previous reported POM‐based electrode materials, thus demonstrating the important role of introducing metal‐organic units in improving capacitive performances. Besides, the electrocatalytic redox activities of complexes 1 – 2 were also studied, both of them can be used as electrochemical sensors to detect Cr(VI) ions. They possess high sensitivity of 0.537 and 0.455 μA μM −1 and low detection limits of 0.16 and 0.33 μM, which are below the maximum content of Cr(VI) in groundwater required by the WHO.