Light-Induced Excited Spin State Trapping effect on [Fe(mepy)3tren](PF6)2 solvated crystals

International audienceA new spin crossover solvated compound [Fe(mepy)3tren](PF6)2.C7H8.C2H3N 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 HS and 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 has allowed 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 photo-induced HS state of similar spin crossover compounds is finally discussed with respect to their structural characteristics