Proton Conduction at High Temperature in High-Symmetry Hydrogen-Bonded Molecular Crystals of Ru III Complexes with Six Imidazole-Imidazolate Ligands.

A new H-bonded crystal [Ru III (Him) 3 (Im) 3 ] with three imidazole (Him) and three imidazolate (Im - ) groups was prepared to obtain a higher-temperature proton conductor than a Nafion membrane with water driving. The crystal is constructed by complementary N-H⋅⋅⋅N H-bonds between the Ru III complexes and has a rare Icy-c* cubic network topology with a twofold interpenetration without crystal anisotropy. The crystals show a proton conductivity of 3.08×10 -5  S cm -1 at 450 K and a faster conductivity than those formed by only HIms. The high proton conductivity is attributed to not only molecular rotations and hopping motions of HIm frameworks that are activated at ∼113 K, but also isotropic whole-molecule rotation of [Ru III (Him) 3 (Im) 3 ] at temperatures greater than 420 K. The latter rotation was confirmed by solid-state 2 H NMR spectroscopy; probable proton conduction routes were predicted and theoretically considered.