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Proton Dynamics of Two-Dimensional Oxalate-Bridged Coordination Polymers

Published

Author(s)

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

Abstract

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.
Citation
Physical Chemistry Chemical Physics
Volume
16
Issue
32

Keywords

neutron scattering, polymers, dynamics, hopping

Citation

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 July 24, 2024)

Issues

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Created August 27, 2014, Updated October 12, 2021