Heat capacity of a five-coordinated iron(III) complex with spin [formula omitted], bromobis( N, N-diethyldithiocarbamato)iron(III), between 0.4 and 300 K

Abstract

Heat capacity measurements have been made for six kinds of specimens prepared by different methods. Among them, Sample A exhibited a A-type ferromagnetic pahse transition at 1.347 K and a Schottky-type anomaly due to the zero-field splitting around 9K. The total entropy and enthalpy were (11.05 ± 0.04) J K −1mol −1 and (97.0 ± 0.4) J mol −1, respectively. Sample B exhibited a Sehottky-type anomaly around 0.4 K due to the ferro-magnetic dimeric coupling with J D k = + 0.30 K as well as the Schottky-type anomaly at 9K. The total magnetic entropy and enthalpy were (11.45 ± 0.03) JK −1 mol −1 and (93.8 ± 0.8) J mol −1, respectively. The remaining samples are simple mixtures of the λ-type modification and the dimeric modification. Irrespective of the magnetic behavior at low temperatures, all the samples showed a non-magnetic first-order phase transition around 270 K. The heat capacity and entropy of this phase transition have been accounted for in terms of the Frenkel theory of heterophase fluctuation. Construction of an adiabatic-type calorimeter workable between 1.5 and 393 K has been also presented.