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

Thermal and pressure effects have been investigated on the [Fe(sal(2)-trien)][Ni(dmit)(2)] spin crossover complex by means of Mossbauer spectroscopic, calorimetric, X-ray diffraction and magnetic susceptibility measurements. The complex displays a complete thermal spin transition between the S = 5/2 and S = 1/2 spin states of Fe-III near 245 K with a hysteresis loop of ca. 30 K This transition is characterised by a change of the enthalpy, Delta H-HL = 7 kJ/mol, entropy, Delta S-HL = 29 J/Kmol, and the unit cell volume, Delta V-HL = 15.4 angstrom(3). 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 similar to 50% upon cooling, indicating a possible (irreversible) structural phase transition under pressure. (C) 2008 Elsevier Ltd. All rights reserved.