Electron density distribution in crystals of potassium trifluorocobaltate(II)

Abstract

The electron density distribution in crystals of KCoF 3 was investigated on the basis of X-ray intensity data collected by diffractometry at 293 K. The characteristic residual electron density around the Co 2+ ion in the octahedral crystal field was observed on the difference Fourier maps when spherical scattering factors were used for the Co 2+ ion. With aspherical scattering factors for the 3d electrons of the Co 2+ ion, structure amplitudes were calculated for two electron configurations, i.e. high spin 4Tg(t2g)5(eg) 2 and low spin 2Eg(t2g)6(eg ). Refinement on the assumption of high spin decreased the R value significantly (0.0077) from that (0.0088) obtained with the spherical refinement, while assumption of low spin increased the value (0.0120). The difference density maps obtained after these refinements also showed that the high-spin (tEg)5(eg) 2 electron configuration is a good approximation of the electronic state for the Co 2+ ion in cubic KCoF 3 crystals at room temperature. [Crystal data: cubic, Pm3m, a = 4.0688 (7)A, V = 67.36 (3)/~3, Z = 1, D x = 3.821 Mg m -3, 2(MoKa) = 0.7107A, /~(Mo Ka) = 7.943 mm -~, T = 293 K; 743 reflections with IFI > 3trlFI.] crystal fields were observed in crystals of y-Co2SiO 4 (Marumo, Isobe & Akimoto, 1977) and CoA120 4 (Toriumi, Ozima, Akaogi & Saito, 1978) respectively. On the deformation density maps of y-C02SiO 4 eight positive peaks were observed around the Co 2+ ion on the lines along the (111 ) directions of the cubic lattice, and six negative peaks on the Co-O bonds. These peaks indicate that the electron density of the t2g orbitals is higher than that of the eg orbitals as a result of splitting of the d orbitals in a quasi-octahedral field. The deformation density around the Co 2÷ ion in CoA120 4 clearly shows that the density on the t2g orbitals is lower than that on the eg, giving an arrangement of negative and positive peaks reversed to that in an octahedral field. The present study was undertaken to increase knowledge on electron density distributions around the transition-metal ions in an octahedral field. In the octahedral crystal field, the ground state of a Co 2+ ion can be either high spin (t2g)5(eg) 2 or low spin (12g)6(eg) depending upon the strength of the crystal field. The refinements were performed for both configurations with aspherical scattering factors and the residual densities after these refinements were compared.