Polymorphism in Dialkylammonium Chlorides. An Adiabatic Calorimetry Study

Abstract

Abstract The heat capacities of four di‐n‐alkylammonium chlorides (di‐n‐pentylammonium chloride, di‐n‐hexylammonium chloride, di‐n‐octylammonium chloride, and di‐n‐decylammonium chloride) were measured from T = 25 K to 350 K using adiabatic calorimetry. All of the compounds investigated were observed to undergo solid‐solid phase transitions in the temperature region examined. The thermodynamic properties obtained for these compounds were compared with those of the layered perovskites (alkylammonium metal halides) and the mono‐n‐alkylammonium chlorides. The high entropies of the solid‐solid phase transitions suggest that there is a significant amount of conformational disorder in the high‐temperature phase, most likely due to solid‐state alkyl‐chain melting, analogous to the layered perovskites and the monoalkylammonium chlorides. The contribution of a CH 2 unit to the heat capacity of these complexes was calculated and compared to the n‐alkanes and the layered perovskites.