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+.