SOLVENT EXCHANGE RATES OF SOLVENT-METAL COMPLEXES FOR FE3+ IN N,N-DIMETHYLFORMAMIDE, ACETONITRILE, AND ETHANOL AND FOR NI2+ IN ETHANOL BY PROTON MAGNETIC RESONANCE

The transverse relaxation rates have been measured for the solvent protons in ethanol solutions of Fe3+ and Ni2+, and N,N-dimethylformamide and acetonitrile solutions of Fe3+ by high-resolution nmr techniques. From the temperature dependence of the relaxation rates the rates and activation parameters have been determined for the exchange of solvent molecules between the first coordination sphere of the metal ion and the bulk solvent. The present results, together with previous work, show that for water, dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile solutions of Fe3+ the solvent exchange rates are all about 0.006 times the corresponding rate in Ni2+ solutions, while in methanol and ethanol solutions of Fe3+ the solvent exchange rates are twice as fast as in the corresponding Ni2+ solutions. This is attributed to steric effects.