PMR AND ESR OF COPPER(II) COMPLEXES INCORPORATING PYRAZINE ANALOGS AS BRIDGING LIGANDS

PMR and ESR spectra were recorded on the crystal powders of pyrazine-2,3-dicarboxylatocopper- (II) and Cu(NO3)2L type complexes (L: 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, quinoxaline, chloropyrazine) at temperatures between 80 and 250 K. From the contact shifts in PMR, spin densities on the carbon atoms of the ligands were evaluated. A σ mechanism and three types of π mechanisms were proposed for the spin delocalization from copper to ligand molecules. The relative magnitude of the contributions from the mechanisms was estimated on the basis of the ESR results. The spin delocalization arises from the combined effect of the σ and π mechanisms, giving rise to antiferromagnefic interaction between copper atoms through the π systems of the bridging nitrogen heterocyclic ligands. © 1979.