Iron(II) closo-borate complexes with 1,2,4-triazole derivatives: Spin crossover in the iron(II) closo-borate complexes with tris(pyrazol-1-yl)methane

Methods of synthesis of iron(II) complexes containing cluster closo-borate anions-[Fe(Htrz)(3)]B10Cl10 (I) (HTrz is 1,2,4-triazole), [Fe(NH(2)Trz)(3)]B10Cl10 center dot 2H(2)O (II) (NH(2)Trz is 4-amino-1,2,4-triazole), [Fe{HC(pz)(3)}(2)]B10Cl10 (III), [Fe{HC(pz)(3)}(2)]B10H10 (IV), and [Fe{HC(pz)(3)}(2)]B12H12 center dot 2H(2)O (V) (HC(pz)(3) is tris(pyrazol-1-yl)methane)-have been developed. The compounds have been studied by the static magnetic susceptibility method (78-500 K) and electronic, IR, and EXAFS spectroscopy. Complexes I and II in the temperature range under consideration remain in the high-spin state. Low-spin complex III shows incomplete spin crossover and decomposes on heating above 440 K. Complexes IV and V are characterized by reversible spin crossover (1) A (1) a double dagger (5) T (2) accompanied by thermochromism (the pink a double dagger white color change). The crossover temperature (T (c)) for IV and V is 375 and 405 K, respectively.