Synthesis, crystal structure, thermal and physical properties of (C6H18N2)3[Sb4Cl18

Abstract

The crystal structure of tris (N, N, N’, N’-tetramethylethylenediammonium) octadecachloridotetraantimonate (III) is built up of [(CH3)2NH(CH2)2NH(CH3)2]2+ cations connected to the one [Sb4Cl18]6n−n anionic chains by N—H⋯Cl hydrogen bonds. In this study, we found that this ionic compound exhibits a triclinic P1¯↔ monoclinic P21/n structural phase transition at about (T1=356±2K) which has been characterized by X-rays powder analysis, DSC, AC conductivity and dielectric measurements. The optical band gap determined by diffuse reflection spectroscopy is 4.38eV for a direct allowed transition. Impedance spectroscopy measurements of (C6H18N2)[Sb4Cl18] were conducted under various frequency settings (from 20Hz to 2MHz) and over the temperature range 309–398K. The Cole-Cole (Z” versus Z’) plots are fitted to two equivalent circuits models. Combined impedance and modulus plots were used as tools to analyze the sample behaviour as a function of frequency at different temperatures. The frequency dependence of the AC conductivity is interpreted in terms of Jonscher’s law. The temperature dependence of the DC and the bulk σp conductivities are well explained by Arrhenius law. The conduction mechanisms are attributed to the quantum mechanical tunnelling (QMT) model in phase I and to the small polaron tunnelling (SPT) model in phase II. Our study has also revealed that the relaxation times are thermally activated and that the dipole process has a non-Debye behaviour.