Spin crossover in heteroligand iron(II) complexes with iris(3,5-dimethylpyrazol-1-yl)methane

Heteroligand iron(II) complexes with tris(3,5-dimethylpyrazol-1-yl)methane (HC(3,5-Me2Pz)3) are synthesized. Along with this ligand, the internal coordination sphere of Fe(II) of the new complexes includes other nitrogen-containing heterocycles, in particular, tetrazole (Tz), pyrazole (Pz), 3,5-dimethylpyrazole (3,5-Me2Pz), and 3-amino-4-ethoxycarbonylpyrazole (Ametcpz), as well as ions NCS− or N(CN)2−. Compounds [Fe(HC(3,5-Me2Pz)3)(Tz)3](NO3)2 (I), [Fe(HC(3,5-Me2Pz)3)(Tz)3](ClO4)2 (II), [Fe(HC(3,5-Me2Pz)3)(Pz)3](NO3)2 (III), [Fe(HC(3,5-Me2Pz)3)(Aecpz)(NCS)2] (IV), and [Fe(HC(3,5-Me2Pz)3)(3,5-Me2Pz)(N(CN)2)2] · 0.5H2O (V) are isolated. The study of the temperature dependence μeff(T) shows the spin crossover 1A1 ⇔ 5T2 accompanied by thermochromism (the color changes from white to pink) in complexes I, II, and IV. The molecular and crystal structures of complex V are determined by X-ray diffraction analysis (CIF file CCDC 994626).