Crystal field model paramagnetic

The intensity ratio between the main and satellite lines has been used to estimate the distance between a paramagnetic centre and protons at surrounding molecules. The method is based on the assumptions that the point dipole approximation applies for the anisotropic hfc, and that this coupling is much smaller than the nuclear Zeeman energy of the proton. It was found advisable to measure this ratio at as high microwave frequency as possible to achieve the latter condition, i.e. Ba < Bn in terms of the direct field model. The procedure was adequate at Q-band but not at X-band to obtain the distance between a proton and the P03 radical in a single crystal of Na2HP03-51120, see [37] for details. 

Pronounced crystal-field effects were observed in the paramagnetic phase NMR for intermetallic compounds of Ce, Pr, Sm or Tm. Crystal-field effects for Tm in TmAlj have been analysed by de Wijn et al. (1970) by a combination of the temperature dependences of the Al Knight shift and of the magnetic susceptibility. These authors also analysed the quadrupole interaction for the Al site in the cubic CujAu structure. Comparing the experimental value e qQ/h = 7.6 MHz with the point-charge model value (Abragam 1961)... 

In this section, we see that valence bond theory addresses how metal-Ugand bonds form and why certain geometries are preferred, while a new model—crystal field theory—addresses why complexes are brightly colored and often paramagnetic. 

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