DSC monitoring of the spin crossover in Fe(II) complexes

Heat flow to [Fe(bzimpy)(2)](ClO4)(2).0.25H(2)O complex (bzimp =2,6-bis(benzimidazol-2-yl)pyridine) (1) was measured between 300 and 460 K by differential scanning calorimetry. This exhibits a well-developed peak characteristic of the first-order phase transitions at temperature 403 K. The enthalpy and entropy of transition from low-spin to high-spin state has been determined to be DeltaH=17 kJ mol(-1) and DeltaS=43.0 J mol(-1) K-1. Heat flow to [Fe(bzimpy(-1H))(2)].H2O Complex (bzimpy(-1H)= deprotonated bzimpy) (II) was measured between 300 and 580 K. The spin crossover in this system is accompanied with liberation of crystal water on the first heating. To monitor the structural changes during the spin crossover, powder diffraction data have been collected as a function of temperature.