Water-Induced Single-Crystal to Single-Crystal Transformation of Ionic Hydrogen-Bonded Organic Frameworks with Enhanced Proton Conductivity

Abstract

Two ionic hydrogen-bonded organic frameworks (iHOF-10, iHOF-11) were prepared using 1,1'-diamino-4,4'-bipyridine diiodide (Dbpy ⋅ 2I) and tetrakis(4-sulfophenyl)ethylene (H₄ TPE). With increasing RH and temperature, water molecules induce single crystal to single crystal (SCSC) transformation of iHOF-10, resulting in the formation of iHOF-11. At 90 °C, 98 % RH, the proton conductivity of iHOF-11 (7.03×10^-3 S cm^-1 ) is 2.09 times higher than iHOF-10 (3.37×10^-3 S cm^-1 ). At 50 °C, 98 % RH, iHOF-11 (9.49×10^-4 S cm^-1 ) is 19.06 times higher than iHOF-10 (4.98×10^-5 S cm^-1 ). The proton conductivity shows water molecules enter the crystal and induce crystal transformation and reorganization of the hydrogen bonding structure, thus increasing the proton conductivity and stability.

Keywords: ionic HOF; proton conductivity; single-crystal to single-crystal transformation; water-induced.