$L_{2,3}$ x-ray absorption spectroscopy and multiplet calculations for $\mathrm{K}M{\mathrm{F}}_3$ and ${\mathrm{K}}_2\mathrm{Na}M{\mathrm{F}}_6$ $(M=\mathrm{N}\mathrm{i},\mathrm{}\mathrm{Cu})$

The electronic structures of nickel and copper have been studied for $\mathrm{K}M{\mathrm{F}}_3$ and ${\mathrm{K}}_2\mathrm{Na}M{\mathrm{F}}_6$ compounds by x-ray absorption spectroscopy at the Ni and Cu $L_{2,3}$ edges in order to characterize the $M-\mathrm{F}$ chemical bond. The spectral features have been interpreted based on the mixing of two ground-state configurations $|{3d}^n〉+|{3d}^{n+1\mathrm{}}〉\underset{¯}{L}.$ Multiplet calculations were used to simulate each spectrum in order to quantify the charge transfer from fluorine to the transition metal yielding a 40% ground-state contribution of the ${3d}^8$ configuration for ${\mathrm{K}}_2{\mathrm{NaCuF}}_6$ and 65% of the ${3d}^7$ configuration for ${\mathrm{K}}_2{\mathrm{NaNiF}}_6.$