Charge densities of two rutile structures: NiF2 and CoF2

X-ray diffraction data were collected at room temperature for two rutile structures, NiF2 and CoF2. Two different crystals of each compound have been used in the experiments. Atomic and thermal parameters were derived from least-squares refinements of high-angle data [(sinθ)/λ≥0.6 A-1]. The results of Fourier inversion of the differences between observed and model structure factors are presented and discussed in terms of difference density maps. The observed charge densities are quantitatively interpreted in terms of: (i) occupation of 3d orbitals; (ii) multipole analysis. A comparison is made between the results obtained from both models. Finally, the charge density features of a series of rutile structures already investigated are compared and discussed. Crystal data: (a) NiF2, Mr=96.71, tetragonal, P42/mnm, a=4.6497(6), c=3.836(6) A, V=66.67 A3, Z=2, Dx=4.818 Mg m-3, λ(Mo Kα)=0.7017 A, μ(Mo Kα)=705.6 mm-1, F(000)=92, room temperature. Final R values (spherical refinement): 0.013 for 137 independent reflections from crystal A; 0.020 for 154 independent reflections from crystal B. (b) CoF2, Mr=96.93, tetragonal, P42/mnm, a=4.6950(7), c=3.1817(5) A, V=70.10 A3, Z=2, Dx=4.590 Mg m-3, λ(Mo Kα)=0.7017 A, μ(Mo Kα)=586.5 mm-1, F(000)=90, room temperature. Final R values (spherical refinement): 0.019 for 140 independent reflections from crystal C; 0.016 for 137 independent reflections from crystal D. (orig.)