Magnetic-Resonance Studies on Copper(II) Complex Ions in Solution. II. Oxygen−17 NMR and Copper(II) EPR in Aqueous Solutions of Cu(en)(H2O)42+ and Cu(en)2(H2O)22+

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Abstract
The temperature dependences of the 17O NMR and Cu(II) EPR spectra of solutions of the ethylenedi‐amine complex ions Cu(en)(H2O)42+ and Cu(en)2(H2O)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17O NMR spectrum is broadened and shifted by Cu(en)(H2O)42+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H2O)22+ has no effect. The Cu(II) EPR spectra of both species have linewidth contributions from spin—rotational relaxation, from tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from 63Cu isotropic hyperfine and 14N isotropic extrahyperfine splitting. The results are discussed in terms of the antibonding molecular‐orbital model for the B1g ground state of Cu(II) and compared with the previous study on Cu(H2O)62+.