PROTON NUCLEAR MAGNETIC-RELAXATION IN AQUEOUS COPPER(II) AMINE CHELATE SOLUTIONS

Nuclear magnetic relaxation dispersion measurements are reported for aqueous solutions of copper(II) ion in solutions of ammonia, 1,2-diaminoethane and triethylenetetraamine. The water proton spin relaxation efficiency is increased dramatically over the hexaaquocopper(II) ion rate when square planar complexes are formed. The major factor contributing to this change is the development of a large hyperfine coupling between the coordinated amine protons and the copper(II) center that dominates low field relaxation rates. The relaxation is generally controlled by the rate of ligand exchange which is catalyzed by high ligand concentration. The triethylenetetraamine complex is substitutionally inert on the time scale of the nuclear spin relaxation and the water proton relaxation induced is dominated by the relative translational motion of the water and the metal center, i.e. outer sphere effects.