Selective Gas Sensing under a Mixed Gas Flow with a One-Dimensional Copper Coordination Polymer.

Structural changes of the coordination polymer associated with gas adsorption (gate opening-type adsorption) can be linked to bulk physical properties such as magnetism, electrical conductivity, and dielectric properties. To enable real-space sensing applications, it is imperative to have a system where the selective adsorption of mixed gases can be correlated with physical properties. In this report, we demonstrate that a crystalline sample of one-dimensional (1D) coordination polymer exhibits selective CO 2 adsorption while simultaneously displaying dielectric switching behavior in a mixed N 2 /CO 2 gas environment. In the crystal of {[Cu 2 (2-TPA) 4 (pz)]·CH 3 CN} n ( 1 ·CH 3 CN), where 2-TPA and pz are 2-thiophencarboxylate and pyrazine, respectively, paddle wheel-type units of [Cu 2 (2-TPA) 4 ] are bridged by pz, forming a 1D chain structure. One of the two crystallographically independent 2-TPA units was interacted with the pz moiety of the adjacent 1D chain by π···π interactions, forming a two-dimensional (2D) layer parallel to the ab plane. Activated 1 shows selective CO 2 adsorption by a gate opening-type adsorption mechanism, indicating that the CO 2 adsorption process is accompanied by a structural change. The change in the real part of dielectric permittivity (ε') under the mixed N 2 /CO 2 gas flow is a result of the selective CO 2 adsorption, which was supported by the enthalpy changes (Δ H ) associated with CO 2 adsorption in two methods: CO 2 adsorption isotherms and temperature-dependent measurements of ε' under a mixed N 2 /CO 2 gas flow. The calculated Δ H values were found to be in good agreement across both methods. The CO 2 ratio in the mixed N 2 /CO 2 gas flow increased, and the switching ratio of ε' (Δε') also increased. Notably, Δε' exhibited a marked increase beyond the pressure required for gate opening adsorption.