Development of novel physical properties derived from proton-dynamics in hydrogen-bonded molecular crystals

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This project aims at developing novel physical properties derived from proton dynamics in hydrogen bonded molecular crystals. There are two main topics to be investigated.1. Elucidation of mechanism of dielectric property derived from tautomerization of beta-hydroxyenones.Hydrogen bond patterns of 3-hydroxyenones, such as 3- or 9-hydroxy phenalenones were determined by X-ray crystallographic analysis and the possibility of tautomerization of these compounds in the crystalline state were investigated by high resolution solid state ^<13>C NMR (CP/MAS) measurements.(1) The SHG active crystal of 3-hydroxyphenalenone was obtained. Hydroxyenone forms a one-dimensional hydrogen-bonded array with short O-O distances (2.58A^^ﾟ).(2) Paraelectric behavior of 2-carboxy-3-hydroxyphenalenone was discovered by dielectric constant measurements. The crystal exhibits antiferroelectric transition at 40K. The switching rate of dipole moment is faster than 10GHz.(3) The disordered crystal structure of 9-hydroxyphenalenone (Phase II 255-280K) was found to be derived from a dynamic origin based on CP/MAS and dielectric measurements. The molecule undergoes not only a rapid tautomerization but also a 120ﾟ jumping motion in crystals and exhibits a paramagnetic behavior.2. Static and dynamic modulation of hydrogen bonds upon the transport property of molecular conductors.Ni(dmit)_2 complexes involving various counter ion systems connected by hydrogen bonds were prepared. Among them, temperature dependence of conductivity of the Ni(dmit)_2 complex carrying H_3O^+-H_2O-CH_3CN as a counter ion system exhibits a hystereses in the temperature range between 230 and 300K. The anomaly may be explained in terms of the dynamical disturbance caused by supercooled water molecules and oxonium ions which melt in this temperature range. The phenomenon may lead to a novel methodology of controlling physical properties based on dynamic processes which take place in the solid state.