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A Preinstalled Protic Cation as a Switch for Superprotonic Conduction in a Metal–Organic Framework

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posted on 04.01.2022, 01:04 authored by Kazuya Otsubo, Shuya Nagayama, Shogo Kawaguchi, Kunihisa Sugimoto, Hiroshi Kitagawa
Metal–organic frameworks (MOFs), made from various metal nodes and organic linkers, provide diverse research platforms for proton conduction. Here, we report on the superprotonic conduction of a Pt dimer based MOF, [Pt2(MPC)4Cl2Co­(DMA)­(HDMA)·guest] (H2MPC, 6-mercaptopyridine-3-carboxylic acid; DMA, dimethylamine). In this framework, a protic dimethylammonium cation (HDMA+) is trapped inside a pore through hydrogen bonding with an MPC ligand. Proton conductivity and X-ray measurements revealed that trapped HDMA+ works as a preinstalled switch, where HDMA+ changes its relative position and forms an effective proton-conducting pathway upon hydration, resulting in more than 105 times higher proton conductivity in comparison to that of the dehydrated form. Moreover, the anisotropy of single-crystal proton conductivity reveals the proton-conducting direction within the crystal. The present results offer insights into functional materials having a strong coupling of molecular dynamic motion and transport properties.