Spin density and bonding in the CrF63– ion in K2Na[CrF6]

Abstract

The spin-density data previously obtained by a polarised neutron diffraction experiment on K₂Na[CrF₆] have been reanalysed. A chemically-based model for the CrF₆^3– ion, involving conventional atomic orbitals, has been fitted to the 92 observed magnetic structure factors using a least-squares procedure. The best refinement, with seven variable parameters, converged with the agreement factors R 0.0861, R′ 0.0579, and χ² 1.569. The spin density in chromium 3d orbitals has t_2g symmetry [t_2g^2.66(5), e_g^–0.06(5)]. There is also a region of spin density centred on the chromium atom which is radially much more diffuse than the theoretical 3d orbitals and contains 0.4(1) spins parallel to the spin density of t_2g symmetry closer to the chromium centre. The model indicates a small parallel spin population [0.020(5)] in each 2p_π orbital of fluorine, and an antiparallel spin population [–0.02(1)] in a fluorine 2p_σ orbital. The model also indicates further antiparallel spin density along the Cr–F vector, and no significant spin population of the fluorine 2s orbital. The spin-transfer coefficients f_s*, f_σ*, and f_π from the present modelling [0.001(3), –0.021(12), 0.020(5) respectively] are shown to be in good agreement with the values determined from other resonance and neutron diffraction techniques.