Stimuli responsive complex salts with ferroelectric switching and thermistor properties Lidija Andros Dubraja , Marko Dunatov, Andreas Puškarić Rudjer Bošković Institute, Croatia Metal-organic materials that respond to external triggers and the environment by altering certain properties are attracting considerable attention because of their potential use in devices. Studying these materials at the molecular level allows us to understand the mechanisms responsible for the stimulus-structure-response property and potentially leads to better-performing and multifunctional devices. The responsiveness of these highly organised structures is the result of flexible structural arrangements, which in most cases are governed by non-covalent interactions. The structural and compositional changes that occur during exposure to different stimuli (e.g., water at different humidity levels or other solvent molecules in the vapour phase) can be monitored very effectively using in situ techniques such as powder X-ray diffraction and infrared spectroscopy. In addition to the structural and spectroscopic changes in these materials, exposure to various stimuli is accompanied in some cases by significant changes in electrical properties, making these compounds attractive for sensing applications. We have tested the electrical properties of two systems composed of ternary and quaternary ammonium cations and complex anions: the well-known bis(oxalato)chromium(III) anion and the understudied (L-tartrato)oxovanadium(V) anion. The dynamics of the structural transformations in the DABCO/ABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane; ABCO = 1-azabicyclo[2.2.2]octane) salts of bis(oxalato)chromium(III) and the tetraethylammonium salt of (L-tartrato)oxovanadium(V) demonstrates the low energy barrier for reversible release and uptake of water molecules from air. 1,2 With careful selection of experimental conditions (temperature, relative humidity), the electrical properties can be varied from proton conductivity, ferroelectricity, or thermistor behaviour. Another interesting property of these complex salts, rarely observed in metal-organic compounds, is pleochroism, an optical phenomenon resulting from the anisotropy of light absorptions allowed by crystal symmetry. References 1. M. Dunatov,A. Puškarić, L. Pavić, Z. Štefanić andL. Androš Dubraja, J. Mater. Chem. C, 2022,10, 8024–8033. 2. M. Dunatov,A. Puškarić and L. Androš Dubraja,J. Mater. Chem. C, 2023, Accepted Manuscript (doi: 10.1039/D2TC05064A).
Financial support by the Croatian Science Foundation (UIP-2019-04-7433) is gratefully acknowledged.
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© The Author(s), 2023
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