Synthesis, characterization and temperature-triggered phase transition of organic-inorganic hybrid compound: (C6H18N2)(HSO4)2

Abstract

A new organic-inorganic hybrid phase transition material, N,N,N’N’-tetramethylethylenediamine dibisulfate (C6H18N2)(HSO4)2, was synthesized via the reaction of CuSO4·5H2O with N,N,N’N’-tetramethylethylenediamine (TMEDA) in sulfuric acid aqueous solution. Differential scanning calorimetry measurement (DSC) discloses that (C6H18N2)(HSO4)2 undergoes a reversible second-order phase transition at 247.7 K with a small hysteresis (ca. 2.5 K). The variable-temperature X-ray single crystal structural analyses indicate that (C6H18N2)(HSO4)2 crystallizes in triclinic system with centrosymmetric space group Pīat low-temperature phase (LTP) and room-temperature phase (RTP). The cell volume of LTP shows an approximately doubling that of RTP and the remarkable differences of cell parameters between RTP and LTP reveal the phase transition. The phase transition of (C6H18N2)(HSO4)2 could be mainly associated with the disorder-order transformation of HSO4ˉ as well as reorientation of the flexible branched chain-like (C6H18N2)2+ cations with decreasing temperature. As expected, the temperature-dependent dielectric constant of (C6H18N2)(HSO4)2 exhibits remarkable peak-like dielectric anomalies around 245 K in accordance with the DSC result. It is expected that all these results could offer an avenue to develop organic-inorganic dielectric material for meeting practical application.