Isotropic Nuclear Resonance Shifts in Some Trigonal Co(II) and Ni(II) Chelate Systems

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Abstract
Well‐resolved high‐resolution proton nuclear resonance spectra have been observed for solutions of Co(II) poly(1‐pyrazolyl) borate chelate systems in CDCl3. In a previous paper [J. P. Jesson, J. Chem. Phys. 45, 1049 (1966)], optical and paramagnetic resonance data have been described for some of these compounds. The combined NMR, EPR, and optical data are treated for a variety of substituted complexes to give a quantitative evaluation of the dipolar contribution to the proton resonance shifts in the ligands. On this basis, an approximate separation of the dipolar and scalar contributions to the shifts is achieved. The scalar contributions are similar to those observed in the corresponding Ni(II) complexes. Some consideration is given to the nuclear relaxation times for the ligand protons in the Co(II) compounds. g‐tensor components for the Co(II) complexes obtained from paramagnetic resonance measurements on magnetically dilute powers at 4.2°K are presented to demonstrate their insensitivity to the effects of ligand substitution.