Polyoxometalate-based metal–organic supramolecular architectures derived from two new pyrimidine-amide ligands as supercapacitors and multifunctional electrochemical sensors

Abstract

Two new polyoxometalate (POM)-based metal–organic supramolecular architectures, [Cu(Hpypa)₂(PMo₁₂O₄₀)(μ₂-Cl)] 3H₂O (1) and [Co(H₂bpap)(γ-Mo₈O₂₈)_0.5(H₂O)₂] H₂O (2), were successfully synthesized by using two self-designed pyrimidine-amide organic ligands [N-(pyridin-3-ylmethyl)pyrimidine-4-carboxamide (pypa) and N,N′-bis(4-pyrimidinecarboxamido)-1,5-pentane (bpap)], as well as Keggin-type POM anions and octamolybdate anions under hydrothermal conditions. Complex 1 is a 1D supramolecular structure containing dinuclear [Cu₂(Hpypa)₄(PMo₁₂O₄₀)₂(μ₂-Cl)₂] units. Complex 2 exhibits a 3D supramolecular framework consisting of 1D [Co(H₂bpap)(H₂O)₂]_n⁴ⁿ⁺ metal–organic chains and free [Mo₈O₂₈]⁸⁻ anions. The supercapacitor performances of complexes 1 and 2 in a three-electrode system were investigated. When the current density is 1 A g⁻¹, 1 and 2 exhibit specific capacitances of 555 and 675 F g⁻¹, respectively. The symmetrical supercapacitor assembled with complex 2 as the electrode modifier exhibits an energy density of 13.4 W h kg⁻¹ with a power density of 450 W kg⁻¹. Capacitance retention remains at 96% after 6500 cycles. At the same time, the electrochemical sensors prepared with complexes 1 and 2 can be used for the determination of Cr(VI)/Fe(III) ions in aqueous solution with high sensitivity and low detection limit.