General trends in phase transitions in an homologous series. Polymorphism in (n-C6H13NH3)2MnCl4 as determined by adiabatic calorimetry from 18 K to 313 K

Abstract

The heat capacity of (n-C₆H₁₃NH₃)₂MnCl₄ has been measured by adiabatic calorimetry from 18 to 313 K. Two structural phase transitions were observed in this compound at T_tr= 206.3 ± 0.1 K (ΔH_tr= 5311 ± 38 J mol^–1, ΔS_tr= 25.73 ± 0.2 J K^–1 mol^–1) and at T_tr= 290.9 ± 0.05 K (ΔH_tr= 10035 ± 24 J mol^–1, ΔS_tr= 37.17 ± 0.1 J K^–1 mol^–1). From comparison with results for the other members of this series with longer alkyl chains, it is concluded that the general trends in their phase transitions are only observed when the number of carbons in the alkyl chains exceeds six.