A Comparative Investigation of Proton Conductivities for Two Metal-Organic Frameworks under Water and Aqua-Ammonia Vapors.

Our investigation on the proton conductivities of two water-stable isostructural 3D Co(II) MOFs, {[Co3 (DMPhIDC)2 (H2 O)6 ]·2H2 O}n (1) [DMPhH3 IDC = 2-(3,4-dimethylphenyl)-imidazole-4,5-dicarboxylic acid] and {[Co3 (m-BrPhIDC)2 (H2 O)6 ]·2H2 O} (2) [m-BrPhH3 IDC = 2-(m-bromophenyl)-imidazole-4,5-dicarboxylic acid], under water or aqua-ammonia vapor shows that the optimized proton conductivities of both 1 and 2 under aqua-ammonia vapor are 4.41 × 10-3 S·cm-1 and 5.07 × 10-4 S·cm-1 (at aqua-ammonia vapor from 1.5 M NH3 ·H2 O solution and 100 °C), respectively, which are approximately 1 order of magnitude greater than those maximum values (8.91 × 10-4 S·cm-1 and 7.64 × 10-5 S·cm-1 ) under water vapor (at 98% RH and 100 °C). The plausible proton pathways and mechanisms of the MOFs have been proposed in terms of the structural analyses, activation energy calculations, water and NH3 vapor absorptions, and PXRD determinations.