Direct Synthesis of Spin‐Crossover Complexes: An Unexpectedly Revealed New Iron‐Triazolic Structure

Spin-crossover complexes form one of the biggest families of switchable compounds. Here we show a new way to obtain spin-crossover materials by direct synthesis from metallic iron. Four complexes of Fe-II with 4-R-1,2,4-triazoles have been synthesized by a direct metal oxidation: [Fe(NH(2)trz)(3)]SO4, [Fe(NH(2)trz)(3)](BF4)(2) and two polymorphs of [Fe(Htrz)(2)(trz)]BF4. Surprisingly high quality of PXRD pattern of [Fe(NH(2)trz)(3)]SO4 allowed to perform Rietveld refinement and obtain reliable crystal structure of the latter. All compounds have been studied by magnetic susceptibility measurements, optical reflectivity, differential scanning calorimetry and Raman spectroscopy. Importantly, spin-crossover characteristics of the complexes obtained by this unusual method are preserved, thus revealing a new effective approach of "direct synthesis" towards switchable coordination compounds.