Proton-Conductive and Electrochemical-Sensitive Sensing Behavior of a New Mn(II) Chain Coordination Polymer

In this work, a novel Mn­(II) chain coordination polymer (Mn-CP), {[Mn­(iip)­(2bbpum)_0.5(H₂O)₃]·2H₂O}_n [H₂iip = 5-iodoisophthalic acid, 2bbpum = N,N′-bis­(2-pyridinemethyl)­oxamide] was synthesized under ambient conditions. Mn-CP further assembles into a 3D supramolecular architecture through hydrogen bonds, halogen bonds, and ππ stacking interactions. The composite Mn-CP/nafion membrane has low activation energy for proton transfer, which results in its temperature-insensitive proton conductivity. The cyclic voltammetry demonstrates that the Mn-CP electrode (Mn-CP/GCE) shows quite different redox properties in 0.1 M H₂SO₄ and 0.1 M PBS aqueous solutions. The Mn-CP/GCE exhibits a couple of irreversible redox peaks with an oxidation peak potential suitable for the nitrite oxidation in 0.1 M H₂SO₄. Quite differently, in the PBS aqueous buffer solution, the Mn-CP electrode has a couple of irreversible redox peaks. The reduction peak potential is appropriate for the H₂O₂ reduction. So, the Mn-CP/GCE can be used not only in the electrocatalytic oxidation of NO₂^– but also in the electrocatalytic reduction of H₂O₂. The amperometric response reveals that the Mn-CP/GCE exhibits high-selective and extremely sensitive oxidation sensing of NO₂^– and reduction sensing of H₂O₂. The exponential detection range is 0.01–20 mM for NO₂^– and 0.01–10.5 mM for H₂O₂. The linear detection range for both H₂O₂ and NO₂^– is 0.01–0.10 mM. The detection limit is 1.865 μM for NO₂^– and 8.57 μM for H₂O₂. The Mn-CP/GCE exhibits high electrochemical stability and fine reproducibility. Moreover, the strategy can be translated to a portable screen-printed electrode (SPE). The Mn-CP/SPE shows more sensitive sensing to NO₂^– and H₂O₂ than Mn-CP/GCE. Moreover, it can detect NO₂^– and H₂O₂ efficiently in the real-world samples. So, Mn-CP may be a potential dual nonenzymatic electrochemical sensory material for NO₂^–via oxidation sensing and H₂O₂via reduction sensing.