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.