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 adsorption while simultaneously displaying dielectric switching behavior in a mixed N/CO gas environment. In the crystal of {[Cu(2-TPA)(pz)]·CHCN} (·CHCN), where 2-TPA and pz are 2-thiophencarboxylate and pyrazine, respectively, paddle wheel-type units of [Cu(2-TPA)] 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 plane. Activated shows selective CO adsorption by a gate opening-type adsorption mechanism, indicating that the CO adsorption process is accompanied by a structural change. The change in the real part of dielectric permittivity (ε') under the mixed N/CO gas flow is a result of the selective CO adsorption, which was supported by the enthalpy changes (Δ) associated with CO adsorption in two methods: CO adsorption isotherms and temperature-dependent measurements of ε' under a mixed N/CO gas flow. The calculated Δ values were found to be in good agreement across both methods. The CO ratio in the mixed N/CO 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.