Effective Approach to Promoting the Proton Conductivity of Metal-Organic Frameworks by Exposure to Aqua-Ammonia Vapor.

We explored the proton conductivities of two 3D CoII metal-organic frameworks (MOFs), {[Co3(m-ClPhIDC)2(H2O)6]·2H2O}n [1; m-ClPhH3IDC = 2-(m-chlorophenyl)imidazole-4,5-dicarboxylic acid] and {[Co3(p-ClPhHIDC)3(H2O)3]·6H2O}n (2; p-ClPhH3IDC = 2-(p-chlorophenyl)imidazole-4,5-dicarboxylic acid), under water and aqua-ammonia vapors, respectively. The experimental results revealed that the proton conductivities of 1 and 2 at aqua-ammonia vapor were 2.89 × 10-2 and 4.25 × 10-2 S/cm, respectively, and approximately 2 orders of magnitude greater than those at water vapor. On the basis of the activation energy, water and ammonia vapor absorption, and powder X-ray diffraction patterns, their proton-conduction mechanisms have been discussed. We believe that this is a novel approach to drastically improving the proton conductivity of MOFs.