PROTON SPIN RELAXATION TIMES (T1 T2) AND MN2+ COMPLEXES IN SOLUTION - PMR AND PULSED NMR STUDIES

The association between paramagnetic Mn2+ ions and dithionite ions S2O42- in aqueous solution assumes a particular significance because of the existence of an equilibrium displaced towards the formation of a complex. Proton spin relaxation times T1 and T2, associated with protons in solution in rapid exchange with protons of water molecules coordinated with the ion Mn2+, are drastically shortened by the presence of the paramagnetic ions. On addition of dithionite ions, an increase in the relaxation times attributable to the presence of an inner-sphere complex is again observed. The observed increase is explained by the variation in the number of coordinated water molecules and the change in correlation times related to dipolar and exchange interactions. The proton spin relaxation data depend on the electron spin relaxation time T2e1 and agree with the values deduced from our EPR studies of the above equilibrium. This investigation has been extended to the association of Mn2+ ion with Cl- and So42- ions. © 1969.