The effect of a magnetic field on the inversion temperature of a spin crossover compound revisited

The compound Mn-III[(pyrol)(3)tren] where (pyrol)(3)tren is the trianionic Schiff base resulting from the condensation of pyrolle-2-carboxaldehyde with 2,2',2''-tris(ethylamino)amine exhibits an abrupt LS (S = 1) <----> HS (S = 2) spin conversion with an inversion temperature in low field of T-1/2 = 43.7 K. The temperature dependence of the heat capacity has been measured. The enthalpy and entropy variations associated with the spin conversion have been found as Delta H = 0.60 kJ mol(-1) and Delta S = 13.8 J K-L mol(-1). The temperature dependence of the magnetization has been measured under various magnetic fields up to 23 T, T-1/2 has been found to decrease as the field increases, first in a smooth fashion, then more rapidly. Under 23 T, T-1/2 is equal to 42.1 K. A theoretical model based on a mean field approximation of the spin crossover phenomenon has been compared with the experimental findings. (C) 2000 Elsevier Science B.V. All rights reserved.