Spin Delocalization in Mixed Tetrahedral Ni II Complexes
摘要:
Proton magnetic resonance spectra of a number of paramagnetic Ni 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.
Spin‐Density Distributions in Conjugated Ligands of Paramagnetic Chelates from NMR Contact Interaction Shifts
作者:D. R. Eaton、A. D. Josey、W. D. Phillips、R. E. Benson
DOI:10.1063/1.1701326
日期:1962.7.15
Electron-spin-density distributions in a variety of π systems have been obtained from proton-contact interaction shifts in paramagnetic nickel II chelates of N,N′-disubstituted aminotroponeimines. The results have furnished a great deal of new information regarding the detailed manner in which π electrons are distributed via conjugative effects. Spin-density distributions in these systems calculated by the valence-bond scheme are shown to be in quite good general agreement with experimental determinations. Effects attributable to hyperconjugation have been observed and the conjugating abilities of linking groups C=C, N=N, NH, O, S, and SO2 have been assessed. It is shown also that metal-ligand π-bond formation results in transfer of 0.1 of an unpaired electron from nickel to the π system of each of the ligands of these bischelates.