Proton Magnetic Resonance Studies of Methanol Solutions of Mn2+, Cu2+, Fe2+, and Fe3+

The transverse relaxation times have been measured for the solvent protons in methanol solutions of Mn²⁺, Cu²⁺, Fe²⁺, and Fe³⁺. From the temperature dependence of the relaxation times 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 kinetic parameters $k_1$ (seconds⁻¹ at 25°C), $\mathrm{\Delta H†}$ (kilocalories), and $\mathrm{\Delta S†}$ (entropy units) are 3.7 × 10⁵, 6.2, and − 12 for Mn²⁺; 10⁸, 10, and 13 for Cu²⁺; 5.0 × 10⁴, 12.0, and 3 for Fe²⁺; and 5.1 × 10³, 10.1, and − 8 for Fe³⁺. A coordination number of 6 was assumed in making the calculations. For all of the divalent ions the OH and CH₃ protons exchanged at the same rate. For the divalent metal‐ion complexes the contact shifts were measured and discussed in terms of the electron delocalization mechanisms.