Solvatomorphism‐induced 45 K hysteresis width in a spin‐crossover mononuclear compound
Résumé
Spin‐transition compounds are coordination complexes that can present two stable or metastable high‐spin and low‐spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi‐stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3‐bpp)2][Au(CN)2]2 (1, 3‐bpp=2,6‐di‐(1H‐pyrazol‐3‐yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3‐bpp)2][Au(CN)2]2⋅2 H2O (1.H2O) already described. 1 has a two‐steps thermal hysteresis of 45 K, in contrast to the compound 1.H2O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single‐crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high‐spin structure, whose symmetry differs from that of the low‐spin phase.
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