Proton conductivity studies on two non-porous coordination complexes with different proton densities

Two new complexes based on the 2,6-dicarboxy-4-hydroxypyridine ligand, formulated as [NaCu 2 (CAM)(HCAM)(H 2 O)]·H 2 O ( 1 ) and [Mn(HCAM)(bim)] ( 2 ) (H 3 CAM = chelidamic acid or 2,6-dicarboxy-4-hydroxypyridine, bim = 2,2′-biimidazole), were synthesized. The two compounds were characterized via their IR spectra, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. Compound 1 features a 1-D zigzag chain constructed by μ 2 -κO1:κO2:κO3:κN1 HCAM 2− and μ 2 -κO6:κO8:κO10:κN2 CAM 3− ligands and Cu( ii ) ions. Complex 2 also shows a 1-D zigzag chain connected by μ 2 -κO6:κO7:κO8:κN2 HCAM 2− ligands, Mn( ii ) ions and terminal H 2 bim ligands. Both complexes are further linked via H-bonding interactions to form 3-D supramolecular networks. Complexes 1 and 2 display a relatively high proton conductivity ( σ ) values of 6.72 × 10 −5 and 1.70 × 10 −4 S cm −1 , respectively, at 85 °C under 100% relative humidity (RH). Notably, although complexes 1 and 2 possess similar structures with 1-D chains, the proton conductivity of 2 is higher than that of 1 because complex 2 has a higher proton density and richer hydrogen bonds stemming from two undeprotonated imidazole rings of the H 2 bim molecules. This work revealed that increasing the proton density of a material by incorporating proton-rich-carriers as auxiliary ligands is an effective strategy to achieve high-performance non-porous coordination polymer-based proton conductors. Two new complexes with similar 1D chain structures using 2,6-dicarboxy-4-hydroxypyridine ligands were obtained. Interestingly, the proton conductivity of 1 is 5.2 times higher than that of 2 because it has a higher proton density.