Large dielectric susceptibility associated with proton transfer in a supramolecular structure of chloranilic acid and 5,5′-dimethyl-2,2′-bipyridine

A 1:1 adduct of chloranilic acid with 5,5(')-dimethyl-2,2(')-bipyridine, in which two kinds of molecules are connected by infinite hydrogen bond chains, exhibits a distinct dielectric phase transition when cooled. Below T-c(=318 K) the hydrogen atoms participating in hydrogen bonding undergo long-range ordering and form an antiferroelectriclike state, taking a single minimum potential in the high-temperature phase (T > T-c) due to the bifurcate hydrogen bond system. The proton-transfer phenomenon was clearly observed by electron density distribution analysis using a maximum entropy method of synchrotron x-ray diffraction data. (c) 2006 American Institute of Physics.