NMR studies of the interaction between Mn 2+ and ClO 4− in aqueous solution

Abstract

Longitudinal and transverse relaxation rates of 1H, 35Cl, and 23Na in aqueous solution containing Mn(ClO 4) 2 and NaClO 4 have been studied as a function of temperature. The water proton relaxation rates are shown not to be affected by high concentrations of NaClO 4. It is shown that the chlorine relaxation of ClO 4 − is dominated by the interaction with the unpaired electron spin of Mn 2+ and that ClO 4 − forms an inner sphere complex with Mn 2+. The rotational correlation time ( τ r ) of ClO 4 − in this complex is 4.6 × 10 −11 sec and the lifetime τ M is less than 7 × 10 −9 sec (300 K). The 23Na + relaxation is dominated by the Mn 2+− 23Na electron-nucleus dipolar interaction and is not dependent on magnetic field. It is shown that Na + is probably separated from Mn 2+ by one water molecule and a rotational correlation time τ r ≥ 7 × 10 −11 sec (300 K) is obtained.