关键词: 热分析, 红外光谱, 相变, 热稳定性, 有序-无序

Abstract: The thermal stability and the solid-solid phase transitions in the [n-C_nH_(2n+1)NH_3]_2CuCl_4 compounds with n=7-12 have been studied by DSC and TG methods. Comparision with C_nZn compounds was made. The nature of three phases of C_9Cu has been discussed in terms of infrared spectroscopy and the assignment of the phase transitions has been given. The thermal stability of C_nCu is lower than that of C_nZn and presents an obvious odd-even effect. All of these compounds exhibit two solid-solid phase transitions in the temperature range of 248-337 K. The peak temperature of phase transitions changes regularly. The peak temperature of the main phase transition increases with the chain length. The total transition enthalpies and entropies increase with increasing chain length. When n≤9, the high temperature phase exists in a partial disorder state. When n≥10, the high temperature phase exists in a conformational disorder state. The main phase transition and the phase transition at 307.7 K of C_9Cu may mainly arise from the change of the packing structure and the change of the partial conformational order-disorder of alkyl chain, respectively.

Key words: Thermalanalysis, Infrared spectroscopy, Phase transition, Order-disorder, Thermal stability