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 [NaCu2(CAM)(HCAM)(H2O)]& BULL;H2O (1) and [Mn(HCAM)(bim)] (2) (H(3)CAM = chelidamic acid or 2,6-dicarboxy-4-hydroxypyridine, bim = 2,2 & PRIME;-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 mu(2)-kappa O1:kappa O2:kappa O3:kappa N1 HCAM(2-) and mu(2)-kappa O6:kappa O8:kappa O10:kappa N2 CAM(3-) ligands and Cu(ii) ions. Complex 2 also shows a 1-D zigzag chain connected by mu(2)-kappa O6:kappa O7:kappa O8:kappa N2 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 (sigma) values of 6.72 x 10(-5) and 1.70 x 10(-4) S cm(-1), respectively, at 85 & DEG;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.