Isotropic Proton Resonance Shifts of Some Bishyphen;(triarylphosphine) Complexes of Cobalt(II) and Nickel(II) Dihalides

摘要

Isotropic proton resonance shifts have been observed for some bishyphen;(triarylphosphine) complexes of cobalt(II) and nickel(II) dihalides. The equations for the pseudocontact shifts were extended to include these complexes which possessgtensors withC2vsymmetry. The isotropic shifts for the nickel complexes are interpreted as arising solely from a contact interaction with unpaired spin in the pgr; orbital of the ligand. Based on the postulate that unpaired spin will distribute itself in the same way in a given ligand whether attached to cobalt or nickel, the shifts for the cobalt complexes are separated into contact and pseudocontact contributions. The relative magnitudes of the pseudocontact shifts correspond well with the expected relative strength of theC2vdistortion of the tetrahedral ligand field of the cobalt complexes. The evaluation of the proportionality constant,QCH3, between the unpaired spin density and the hyperfine interaction constant for the methylhyphen;substituted complexes demonstrates the consistency of the interpretation of the shifts. The difference in the unpaired spin densities on the cobalt and nickel complexes is explained by slightly greater interelectronic respulsion in thetorbitals of the nickel complexes.