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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 ZnADP𔅗H2O with the highest proton conductivity (8 x 10-3 Scmu-1^, 25 °C, 98% RH). Its isostructural derivative ZnKADP𔅖H2O, in which ammonium ions are substituted by potassium ions, we also measured to investigate the role of ammonium ions. ZnADP𔅗H2O and SnKADP𔅗H2Oexhibit 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 ZnKADP𔅗H2O two similar relaxations above each transition temperature. The two relaxations of ZnADP𔅗H2 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.
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], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=915859
(Accessed October 9, 2025)