Investigation of the thermal and conductive properties of oxalic acid salts with planar and undulating proton-conducting layers

Abstract

The physical properties of two proton conductors 1H-1,2,4-triazol-4-ium hydrogen oxalate (TriOX) and 1H-imidazol-3-ium hydrogen oxalate (ImiOX) were investigated. For the ImiOX salt, we observed undulating conducting layers with cations protruding by about 20° above and below the anion plane, in contrast to the TriOX salt, in which the layers were planar. The effect of undulating conducting layers on the thermal and conductive properties of oxalic acid salts is discussed. The ImiOX salt, which contains undulating layers, exhibits a higher conductivity value (σ_dc = 1.2 × 10⁻⁴ S m⁻¹ at 493 K) than the TriOX salt with a planar structure (σ_dc = 1.2 × 10⁻⁶ S m⁻¹ at 449 K). Theoretical analysis of the Hirshfeld surface and the quantum theory of atoms in molecules (QTAiM) show that there are stronger interactions in ImiOX. The imidazolium salt has better thermal stability compared to TriOX.