The Magnetic Properties of Iron(II) Complexes with 2-(2′-Pyridyl)imidazole and Its Derivatives

The magnetic susceptibilities and Mössbauer spectra of iron(II) complexes of 2-(2′-pyridyl)imidazole (PI), 2-(6′-methyl-2′-pyridyl)imidazole (6-MPI), and 2-(2′-pyridyl)benzimidazole (PBI) have been measured in the 4.2–298 K temperature range. The results show that Fe(II)(PI)3(ClO4)2H2O and Fe(II)(PBI)3(ClO4)2H2O have a spin equilibrium between 1A1 and 5T2, while Fe(II) (6-MPI)3(ClO4)2H2O does not have such an equilibrium. The temperature dependence and magnitude of the magnetic data for Fe(II)(PBI)3(ClO4)2H2O and Fe(II)(6-MPI)3(ClO4)2H2O have been calculated by using a parametric Iigand-field approximation. The results indicate that the orbital splittings of the 5T2 ground state due to trigonal distortion are −2000 and −800 cm−1 for Fe(II) (6-MPI)3(ClO4)2H2O and Fe(II)(PBI)3(ClO4)2H2O respectively.