• Iron;
  • Spin crossover;
  • Cubane structure;
  • Hydrogen bonds;
  • Stepwise SCO;
  • Hysteresis


A spin-crossover iron(II) complex, fac-[FeII(HLn-Hx)3]Cl·PF6 (1), that exhibits stepwise spin transition and thermal hysteresis was synthesized by using the ligand 2-methylimidazol-4-ylmethylidene-n-hexylamine (HLn-Hx). Four complex cations (fac-[FeII(HLn-Hx)3]2+) and four Cl anions associate through twelve imidazole···Cl H bonds to give a tetrameric cubane-like assembly, and one PF6 anion is encapsulated within the cavity of the cubane. Magnetic susceptibility measurements showed a three-step spin transition, and the spin-crossover profile became less pronounced as the sweep rate increased. At a sweep rate of 0.5 K min–1, the midpoint temperatures of the three steps are Tc([UPWARDS ARROW]) = 131.2, 144.2, and 154.2 K in the heating mode and Tc([DOWNWARDS ARROW]) = 116.8, 137.8, and 151.8 K in the cooling mode. The respective thermal hystereses were evaluated to be 14.4, 6.3, and 2.4 K wide.