Heat capacity and phase transitions of the plastic crystal formylferrocene

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 Delta H = (0.887 +/- 0.01) kJ mol(-1)/Delta S = (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 call reorient quasi-isotropically in the solid state. This situation bears a close resemblance to that encountered in fullerene C-60.