Novel metal(ii) coordination polymers based on N,N′-bis-(4-pyridyl)phthalamide as supercapacitor electrode materials in an aqueous electrolyte

Abstract

Based on the redox-active L (N,N′-bis-(4-pyridyl)phthalamide) ligand, two porous MOFs formulated as Zn₆(BPC)₆(L)₃·9DMF (H₂BPC = 4,4′-biphenyldicarboxylic acid) (1) and Cd₂(TDC)₂(L)₂·4H₂O (H₂2TDC = 2,5-thiophenedicarboxylic acid) (2) were synthesized and structurally characterized by single-crystal X-ray diffractions. Complex 1 features a uninodal 5-connected 3-fold interpenetrated 3D framework with {4⁶.6⁴}-bnn hexagonal BN topology. Complex 2 displays a uninodal 6-connected 2-fold interpenetrated 3D framework with {4¹².6³}-pcu topology. When complexes 1 and 2 are used as supercapacitor electrode materials, they can provide a large voltage window as high as 2.6 V in an aqueous electrolyte, and their specific capacitances are much more than the value for the bare carbon glassy electrode. It is observed that the more the current density, the less the specific capacitance for the two kinds of supercapacitor electrode materials. The two complexes show different thermal stabilities, UV absorption and photoluminescence properties.