Spin Delocalization in Mixed Tetrahedral Ni II Complexes

Authors:
Publisher website
Google Scholar
Abstract
Protonmagnetic resonance spectra of a number of paramagneticNi II chelates of the type NiL1L2 where L1 and L2 are different aminotroponeimine ligands have been examined. The proton resonances show large hyperfine contact interaction shifts due to delocalization of spin density from the metal to the ligand by dπ—pπ bonding. In the series of mixed chelates the amount of spin density delocalized to the different ligands varies markedly. Comparison with the spectra of the symmetric chelates shows that one ligand of each of the mixed chelates gains in spin density at the expense of the other ligand. The effect has been found to depend on the electron withdrawing or donating properties of the ligand substituents. The results for a number of ligands containing substituted phenyl groups have been correlated with the Hammett σ parameters. Two possible interpretations of these results are discussed, one proposed by Lin and Orgel and the other suggested by Jaffe's ideas of competitive π bonding in tetrahedral complexes. The latter is preferred for the Ni II aminotroponeimineates.

This publication has 8 references indexed in Scilit: