Anomalous Spin Transition Observed in Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) Thiocyanate Dihydrate


  • The authors wish to express their gratitude to Ms. P. Räder and Ms. E. Muth of the Max-Planck-Institute for Polymer Research, Mainz for their help in carrying out the DSC and TGA measurements. Financial support from the Deutsche Forschungsgemeinschaft (Priority Program “Molecular Magnetism”), the Fonds der Chemischen Industrie, the Materialwissenschaftliches Forschungszentrum of the University of Mainz and the Australian Research Council is gratefully acknowledged.


Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) thiocyanate dihydrate undergoes a two-step singlet (1A1) ⇄ quintet (5T2) transition in which both steps are associated with thermal hysteresis. Thermal cycling of the sample results in its conversion to a second phase which displays a single-step transition with a very narrow hysteresis loop. This second phase slowly reverts to the initial phase on standing at 300 K. The interconversions are completely reversible. The spin state changes have been monitored by measurement of magnetism and Mössbauer spectra and by differential scanning calorimetry (DSC) studies.