Spin crossover in a tetranuclear Cr(III)-Fe(III)3 complex

A novel heteronuclear exchange-coupled complex [Cr I I I {(CN)Fe I I I -( 5 L)} 3 (CN) 3 ] containing a pentadentate blocking ligand 5 L was synthesized. The X-ray structure shows that a meridional isomer applies with inequivalent Fe I I I centers. The complex exhibits a thermally induced spin crossover along with the exchange coupling. Mossbauer spectra indicate a spin transition between S = ½ and S = 5/2 states although a considerable amount of Fe I I I centers stays high-spin at T = 6 K. The magnetization, the magnetic susceptibility, and the Mossbauer data were fitted in one run with a spin crossover model taking into account exchange interactions among all metal centers.