A nuclear magnetic resonance study of the ${\mathrm{F}}^{19}$ resonance in a single crystal of KNi${\mathrm{F}}_3$ is reported. The internal fields at the fluorine nuclei were measured. Interpretation of the measured fields showed that the spin densities in the fluorine $2s$ and $2p\sigma$ orbitals were (0.538±0.05)% and (3.78±0.2)%, respectively. A comparison with the KMn${\mathrm{F}}_3$ measurements, where $p\pi$ interactions are allowed, indicated the importance of $p\pi$ bonding in these crystals. It is shown that only a model which allows the $2s$, $2p\sigma$, and $2p\pi$ electrons individual degrees of covalency can explain the observations.

• Received 14 December 1962

DOI:https://doi.org/10.1103/PhysRev.130.506