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1D Metal-Oxalates H2DABCO[M(C2O4)2]·3H2O (M(II): Co, Mg, Zn): Phase Transitions, Magnetic, Dielectric, and Phonon Properties

Abstract

A family of 1D hybrid organic–inorganic metal oxalates H2DABCO[M(C2O4)2]·3H2O (where H2DABCO diprotonated 1.4-diazoniabicyclo[2.2.2]octane and M(II): Co, Mg, Zn) displays paraelectric to ferroelectric phase transition between 203 and 217 K, triggered by rearangement of crystalline water present in the crystal structure. The symmetry decreases from P21/n to P21. We demonstrate that spontaneous electric polarization arises due to the release of dipolar crystalline water from steric hindrances present in paraelectric phase. The increased dynamics of water in the ferroelectric phase is preceded by the significant reconstruction of hydrogen-bond network. Breaking of hydrogen bonds leads to elongation of the metal-oxalate chains resulting in negative thermal expansion in the c-direction as well as distortion of the uncoordinated oxalate ligands. The analysis of IR modes confirm the mechanism of the phase transition while the broadband dielectric spectroscopy approves significant reduction of activation energy assigned to water rotation at low temperatures. Investigated metal-oxalates act as microporous materials above room temperature, by loosing (with heating) and recovering (with cooling) crystalline water. The compounds show switchable dielectric behaviour related to ferroelectric phase transition. Additionally, Co analogue exhibits spin-canted antiferromagnetic ordering at 7 K and, by extension, is the first multiferroic homometallic 1D oxalato-bridged coordination polymer

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Supplementary files

Article information


Submitted
12 Jan 2020
Accepted
25 Mar 2020
First published
25 Mar 2020

J. Mater. Chem. C, 2020, Accepted Manuscript
Article type
Paper

1D Metal-Oxalates H2DABCO[M(C2O4)2]·3H2O (M(II): Co, Mg, Zn): Phase Transitions, Magnetic, Dielectric, and Phonon Properties

K. Pasińska, A. Ciupa, A. Pikul, A. Gągor, A. Pietraszko and A. Cizman, J. Mater. Chem. C, 2020, Accepted Manuscript , DOI: 10.1039/D0TC00192A

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