H-bonding interactions enable a 3D pillared cobalt (II) coordination polymer for touchless finger moisture detection

Coordination polymers (CPs) are emerging as the next generation of macromolecule materials in many industrial and technological applications, e. g. gas/humidity sensing. The design of CP-based sensors with high performance and low cost is of significance, but this work is still in the infancy stage. In this contribution, a new one dimensional (1D) CP has been successfully synthesized by a simple solvent evaporation method at room temperature, namely [Co(DPP)(H 2 O) 2 ] n ·(TCA) 2 (H 2 O) 4 (named as Co-1, HTCA = 3-thiophenezoic acid, DPP = 1, 3‑di(4‑pyridyl)propane). The Co-1 structure contains abundant H-bonding interactions, weaving it from 1D chain structure into three dimensional (3D) pillared-layer structure. As an impedimetric humidity sensing material, this CP exhibits short response time, small hysteresis, excellent repeatability, and good stability in the working range of 11%–97% relative humidity (RH). Furthermore, it also shows excellent performance in monitoring the moisture content of human finger skin. By analyzing the complex impedance spectra, the humidity sensing mechanism of Co-1 sensor was expounded at different RH ranges.