Magnetic properties of trigonally distorted octahedral iron(II) complexes

Abstract

The principal and average magnetic susceptibilities of FeSiF₆,6H₂O and FeGeF₆,6H₂O have been measured in the temperature range 300–80 °K. Theoretical magnetic moments have been calculated for a free-ion ⁵D basis, perturbed by a trigonal crystal-field and spin–orbit coupling. A crystal field (D_3d) point-charge calculation was parameterized by the second- and fourth-order radial parameters Cp and Dq, and an angular parameter θ. For Cp > Dq the mixing of the two trigonal ⁵E_g terms by spin–orbit coupling and the crystal field altered the theoretical principal magnetic moments from those calculated for a ⁵T_2g cubic-field basis set. The low experimental moments of the complexes [as compared to the near tetragonal (NH₄)₂Fe(SO₄)₂,6H₂O] derives from the sensitivity of the ground-state splitting, Δ, to θ when Cp is large: and this appears to be characteristic of the trigonal nature of the distortion. Assuming λ=kλ₀ and Dq= 1000 cm.^–1 ambiguous fits with ranges of values of Cp, k, and θ have been found. It was not possible to resolve these ambiguities by use of optical, Mössbauer, or e.s.r. spectra.

The magnetic properties of the ⁵D term perturbed by a tetragonal crystal-field and spin–orbit coupling, have been briefly investigated and susceptibilities of Fe(NH₄)₂(SO₄)₂,6H₂O discussed.