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+

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 B_1g ground state of Cu(II) and compared with the previous study on Cu(H₂O)₆²⁺.