Search

The compound Fe[C(SiMe3)3]2 has been prepared and investigated by the means of powder X-ray diffractometry and 57Fe Mossbauer spectroscopy. The compound’s unique geometry, in which iron is linearly coordinated by the two C(SiMe3)3 ligands, results in a unusual electronic structure of iron, which is visualized as an extreme high hyperfine magnetic field of 157.5(8) T as sensed by the 57Fe nucleus at T = 20 K. In order to obtain information on the electronic structure of iron and on the bonds to the ligands, DFT (density functional theory) calculations were carried out on Fe[C(SiMe3)3]2. The high-spin state of iron was found to be energetically favored: an Fe(II) electron configuration of 3d5.83 4s0.72 is predicted, where the 4s electron density is only slightly polarized, and most of the unpaired electrons have 3d character. By assuming a linear crystal field, and associated 3d level scheme as a starting point, it is suggested that the extreme high hyperfine magnetic field, observed along with an apparently negative quadrupole splitting, is perpendicular to the C–Fe(II)–C bond axis, and can be decomposed mainly into contact (B c ≈ 44 T), dipolar (B d ≈ 14 T), and orbital (B L ≈ 99 T) hyperfine magnetic field contributions.

Fe[C(SiMe3)3]2 compound, in which iron is coordinated by two carbons, was prepared using the reaction of FeCl2 with (Me3Si)3CLi, and investigated by XRD, 57Fe Mossbauer spectroscopy and DFT calculations. 157.5 T hyperfine magnetic field was found at the site of the iron nucleus of this compound at 20 K. DFT calculations predict the quintet states to be clearly favored energetically over the lower spin states. The population analysis reveals considerable 4s as well as large unpaired 3d electron contributions, which can be responsible for the extremely high hyperfine field.