Nuclear Magnetic Resonance Spectroscopy. Use of Carbon-13 Isotropic Shifts as a Probe of Mechanisms of Spin Transmission in Metal Complexes. Some Pyridine-Type Bases and Triphenylphosphine Complexed to Nickel(II) and Cobalt(II) Acetylacetonates

The theory of isotropic nmr chemical shifts produced by transition metal ions with unpaired electrons suggests that the relative signs and magnitudes of the proton and ^(13)C isotropic shifts should be directly related to the mode by which unpaired spin density is transmitted from the metal to the ligand. It has been concluded that the shifts observed in the ^(13)C and ^1H spectra of some pyridine-type bases and triphenylphosphine complexed to cobalt(II) and nickel(II) acetylacetonates are indicative of spin density in both the CT and T frameworks of the ligands. The IC isotropic shifts appear to be controlled mainly by contact interactions