Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

Abstract

Thermal and pressure effects have been investigated on the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex by means of Mössbauer spectroscopic, calorimetric, X-ray diffraction and magnetic susceptibility measurements. The complex displays a complete thermal spin transition between the and spin states of FeIII near 245 K with a hysteresis loop of ca. 30 K. This transition is characterised by a change of the enthalpy, ?HHL=7 kJ/mol, entropy, ?SHL=29 J/Kmol, and the unit cell volume, ?VHL=15.4 Å3. Under hydrostatic pressures up to 5.7 kbar the thermal transition shifts to higher temperatures by ca. 16 K/kbar. Interestingly, at a low applied pressure of 500 bar the hysteresis loop becomes wider (ca. 61 K) and the transition is blocked at ~50% upon cooling, indicating a possible (irreversible) structural phase transition under pressure.