Heat capacity and phase transitions of the plastic crystal formylferrocene

Abstract

Heat capacities of the plastic crystal formylferrocene have been measured with adiabatic calorimetry in the 13–405 K temperature region. Three phase transitions hitherto reported were observed at 293.53 K (second-order phase transition), 317.03 K (first-order phase transition to plastic crystal phase), and 397.60 K (fusion). The enthalpy and entropy of transition were determined as ΔH = (0.887 ± 0.01) kJ mol−1/ΔS = (3.39 ± 0.05) J K−1 mol−1, (13.29 ± 0.01) kJ mol−1/(42.10 ± 0.01) J K−1 mol−1, and 2.76 kJ mol−1/6.88 J K−1 mol−1, respectively. Mechanisms governing the phase transitions are discussed. Because formylferrocene has an almost spherical molecular structure, it can reorient quasi-isotropically in the solid state. This situation bears a close resemblance to that encountered in fullerene C60.