A proton transfer mechanism along the PO4 anion chain in the [Zn(HPO4)(H2PO4)]2− coordination polymer

In this study, we revisit the proton transfer mechanism in [Zn(HPO4)(H2PO4)]2−, a coordination polymer possessing high proton conductivity. In a previous report [N. Phattharasupakun, J. Wutthiprom, S. Kaenket, Th. Maihom, J. Limtrakul, M. Probst, S. S. Nagarkar, S. Horike and M. Sawangphruk, Chem. C...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2019-01, Vol.21 (34), p.18605-18611
Main Authors: Dong, Hieu C, Hoang, Hieu T, Tran, Dinh Manh, Phan, Thang B, Bureekaew, Sareeya, Kawazoe, Yoshiyuki, Le, Hung M
Format: Article
Language:English
Subjects:
Anions
Chain mobility
Coordination polymers
Ions
Polymers
Protons
Rotation
Unit cell
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Summary:In this study, we revisit the proton transfer mechanism in [Zn(HPO4)(H2PO4)]2−, a coordination polymer possessing high proton conductivity. In a previous report [N. Phattharasupakun, J. Wutthiprom, S. Kaenket, Th. Maihom, J. Limtrakul, M. Probst, S. S. Nagarkar, S. Horike and M. Sawangphruk, Chem. Commun., 2017, 53, 11786–11789], it was hypothesized that protons could move along the ImH+ chain involving phosphate anions within the polymer structure, with energy barriers >1.3 eV. Adopting M06-2X calculations to examine the reaction pathway, we observe that it is much more favorable for H+ to move along a one-dimensional channel formed by HPO42− and H2PO4− anions. Within a unit cell, the proton hopping process can be divided into three elementary steps. For the forward proton transfer direction, the maximum energy barrier is only 0.04 eV, while that of the backward direction is 0.27 eV. Even though the barriers of the backward direction seem to outreach the barriers of the forward direction, both are still low in comparison with those reported in the literature. Moreover, we also point out the involvement of PO4 rotation during the proton transfer process. Activation energies of 0.37 eV and 0.15 eV are required for single steps of rotation of the phosphate anion. Both H+ translation (hopping) and rotation steps of PO4 anions simultaneously participate in the course of proton transfer in the coordination polymer.
ISSN:1463-9076
1463-9084
DOI:10.1039/c9cp04216d