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Proton Dynamics of Two-Dimensional Oxalate-Bridged Coordination Polymers



Satoshi Miyatsu, Maiko Kofu, Atsushi Nagoe, Takeshi Yamada, Masaaki Sadakiyo, Teppei Yamada, Hiroshi Kitagawa, Madhu Sudan Tyagi, Victoria Garcia Sakai, Osamu Yamamuro


A two-dimensional porous coordination polymer (NH4)2HOOC(CH2)4COOH}[ZN2(Co2O4)3] (abbreviated to ZnADP), which accommodates water molecules between the [Zn2(C2O4)3] layers, is highly remarked as a new-type crystalline proton conductor. In order to investigate its phase behavior and proton conducting mechanism, we have performed adiabatic calorimetry, neutron diffraction, and quasi-elastic neutron scattering experiments on a fully hydrated sample ZnADP&#82263H2O with the highest proton conductivity (8 x 10-3 Scmu-1^, 25 °C, 98% RH). Its isostructural derivative ZnKADP&#82262H2O, in which ammonium ions are substituted by potassium ions, we also measured to investigate the role of ammonium ions. ZnADP&#82263H2O and SnKADP&#82263H2Oexhibit higher-order transition at 86 K and 138 K, respectively. From the magnitude of transition entropy, the former is of an order-disorder type while the later of a displacive type. ZnADP°3Hd2O has four Debye-type relaxations and ZnKADP&#82263H2O two similar relaxations above each transition temperature. The two relaxations of ZnADP&#82263H2 with very small activation energies (Δ}Ε < 5 kJmol01) are due to rotational motions of ammonium ions and play important roles in the proton conduction mechanism. It was also found that the protons in ZnADP°3H2O are carried through a Grotthus mechanism. We present a discussion on the proton conducting mechanism based on the present structural and dynamical information.
Physical Chemistry Chemical Physics


neutron scattering, polymers, dynamics, hopping


Miyatsu, S. , Kofu, M. , Nagoe, A. , Yamada, T. , Sadakiyo, M. , Yamada, T. , Kitagawa, H. , Tyagi, M. , Garcia Sakai, V. and Yamamuro, O. (2014), Proton Dynamics of Two-Dimensional Oxalate-Bridged Coordination Polymers, Physical Chemistry Chemical Physics, [online], (Accessed June 1, 2023)
Created August 27, 2014, Updated October 12, 2021