Magnetic Resonance Studies on Copper (II) Complex Ions in Solution. III. NMR and EPR in Concentrated Ethylenediamine Solutions

Measurements of the proton and 14N NMR linewidths in ethylenediamine—water solutions of Cu(II) combined with EPR studies of Cu(II) in these media demonstrate that the first sphere relaxation and residence times both make singificant contributions to the over-all relaxation of protons and 14N by Cu(II). Moreover, the results are consistent with the view that protons and 14N both experience the Cu(II) evironment through exchange of the ethylenediamine molecule as a whole between the bulk solvent and the Cu(II) first sphere. From the temperature dependence of the Cu(II) EPR linewidth it is further concluded that the relaxation of the electron spin occurs predominantly via the spin—rotational process at higher temperatures. At lower temperatures the EPR linewidth is broadened both by tumbling of a tetragonally distorted complex with an anisotropic g factor and hyperfine coupling constant and by the same fast chemical exchange process which provides 14N and proton relaxation in ethylenediamine.