Light-induced excited spin state trapping effect on [Fe(mepy)_3tren](PF_6)_2 solvated crystals

摘要

A spin-crossover solvated compound [Fe(mepy)3tren](PF_6)_2?C_7H_8?C_2H_3N has been prepared and its switching properties have been compared to those reported for the non-solvated solid. The thermal spin transition occurs at 88 K with the opening of a 3.5 K wide hysteresis loop, while a fairly steep transition at 215 K without hysteresis has been previously reported for the non-solvated analogue. This feature has been rationalized by the analysis of the high-spin (HS) and low-spin (LS) structures, evidencing a relative stabilization of the high-spin state, as well as strong intermolecular interactions in the solvated compound. The photoswitching of the solvated solid, based on the light-induced excited spin state trapping effect, leads to a quantitative transformation from the low-spin to the high-spin state at 10 K. The long lifetime of the metastable HS state at 10 K allows the measurement of the photo-induced HS structure, where the cooperative interactions are enhanced, compared to those of the thermally populated HS structure. Then,the HS-to-LS relaxations have been studied between 45 and 60 K. They are sigmoidal in shape and can be well fitted in the frame of the mean-field approximation. The relative stability of the photoinduced HS state in this family of spin crossover compounds is not directly related to their thermal spin transition temperature. This unexpected observation is rationalized by a careful analysis of their structural characteristics.