Manipulation of multi-functions in molecular materials is promising for future switching and memory devices, although it is currently difficult. Herein, we assembled the asymmetric {Fe 2 Co} unit into a cyanide-bridged mixed-valence chain {[(Tp)Fe(CN) 3 ] 2 Co(BIT)} • 2CH 3 OH (1) (Tp = hydrotris(pyrazolyl)borate and BIT = 3,4-bis-(1H-imidazol-1-yl)thiophene), which showed reversible multi-phase transitions accompanied by photo-switchable single-chain magnet properties and a dielectric anomaly. Variable-temperature X-ray structural studies revealed thermo-and photoinduced selective electron transfer (ET) between the Co and one of the Fe ions. Alternating-current magnetic susceptibility studies revealed that 1 displayed on and off single-chain magnet behavior by alternating 946-nm and 532-nm light irradiation. A substantial anomaly in the dielectric constant was discovered during the electron transfer process, which is uncommon in similar ET complexes. These findings illustrate that 1 provided a new platform for multi-phase transitions and multi-switches adjusted by selective metal-to-metal ET.
The incorporation of two different cyanide building blocks of [(Tp R )Fe III (CN) 3 ] − and [Au I (CN) 2 ] − into one molecule afforded a novel hexanuclear [Fe III 2 Fe II 2 Au I 2 ] complex (1•2Et 2 O), in which the cyanide-bridged [Fe III 2 Fe II 2 ] square was further grafted by two [Au I (CN) 2 ] − fragments as long arms in syn orientations. Complex 1•2Et 2 O undergoes a gradual spin crossover (SCO) ffrom low-spin (LS) to high-spin (HS) state for the Fe(II) centers upon desolvation.Remarkably, its desolvated phase (1) exhibits a reversible but atypical two-step (sharp−gradual) SCO behavior with considerable hysteresis (21 K). Variabletemperature single-crystal X-ray structural studies reveal that the hysteretic spin transition takes place synchronously with the concerted displacive motions of the molecules, representing another rare example including multistep and hysteretic spin transitions due to the synergetic SCO and structural phase transition.
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