Theory of the Isotropic NMR Shifts in Trigonal Co(II) Complexes

The theory of both the contact and pseudocontact shift in Co(II) trigonal complexes is considered. The theory predicts a pseudocontact shift in Co(II)poly(1‐pyrazolyl)borate complexes, in good agreement with experimental results. The predicted contact shifts are found to be much different from that predicted by previously proposed theories. In the region of 200–400°K, the temperature dependence is found to deviate strongly from a $\text{1\hspace{0.17em}/\hspace{0.17em}T}$ dependence for the pseudocontact shift but not for the contact portion of the shift. The assumption made in earlier theories, that the contact interaction is the same for all six Kramer's doublets, is examined in detail.