Synthesis, crystal structures and high-temperature spin-crossover of new inclusion compounds of iron(II) tris(pyrazol-1-yl)methane complex with p-sulfonatocalix[4]arene

Three new inclusion compounds based on iron(II) tris(pyrazol-1-yl)methane [Fe{HC(pz)3}2]2+ cation and p-sulfonatocalix[4]arene (C[4]AS) as a counterion have been synthesized in the solid state. The magnetochemical investigation (μeff) of the dehydrated complex [Fe{HC(pz)3}2]5(C[4]AS)2 has shown a high-temperature 1А1 ⇔ 5Т2 spin crossover (390 K) which was accompanied by thermochromism. [Display omitted] •The effect of inclusion on the spin-crossover in the iron(II) complex was shown.•The inclusion of [Fe{HC(pz)3}2]2+ into cavity of calix[4]arene is proved by XRD.•A decrease of SCO temperature and an increase in thermal stability are found. Novel inclusion compounds based on iron(II) tris(pyrazol-1-yl)methane [Fe{HC(pz)3}2]2+ cation and p-sulfonatocalix[4]arene (C[4]AS) as a counterion of formulas [Fe{HC(pz)3}2]2(C[4]AS)·24H2O (II) and [Fe{HC(pz)3}2]5(C[4]AS)2·62H2O (III) have been synthesized in the solid state and studied by SC-XDR. The inclusion of [Fe{HC(pz)3}2]2+ cation into the macrocycle cavity with 1:1 host-guest stoichiometry in both cases was found. The magnetochemical investigation (μeff) of the dehydrated complex I of formula [Fe{HC(pz)3}2]5(C[4]AS)2 in the 78–500 K temperature range has shown a high-temperature 1A1 ⇔ 5T2 spin crossover (SCO) which was accompanied by thermochromism. The crossover temperature values for heating (Tc↑) and cooling (Tc↓) are equal to 390 K and 380 K, respectively.