Complete spin crossover in the [Fe(pybzim)3](ClO4)2·H2O Complex

The magnetic properties of a hexacoordinated Fe(II) complex with the bidentate ligand 2-(2-pyridyl)benzimidazole (pybzim)3 - [Fe(pybzim)3](ClO4)2·H2O have been investigated by AC susceptometer measurements. The temperature dependence of the AC magnetic susceptibility for a powder sample showed essentially diamagnetic behaviour below 85 K and paramagnetism (μeff/μB = 4.5 - 5.3, S = 2) above 160 K, obeying the Curie-Weiss law. Spin crossover behaviour can be found within the temperature range of 90 to 160 K; it is centred at 141 K. The complex is ESR silent in X-band mode: neither the powder sample (77 and 300 K) nor a methanol solution exhibit an ESR signal. The spin-crossover transition of a freshly prepared powder sample is complete. However, time evolution causes (within months) an increasing admixture of iron(II), which was proved by magnetic susceptibility measurement, ESR, and electron spectra of the complex. (authors)