WATER PROTON RELAXATION FOR SOME LANTHANIDE AQUA IONS IN SOLUTION

The nuclear magnetic relaxation dispersion (NMRD) profiles of water protons have been investigated between 0.01 and 600 MHz for lanthanide aqua complexes, where the lanthanide is Pr, Sm, Dy, Ho, Er, and Yb. The experimental profiles have been interpreted as due to contributions from proton-electron dipolar coupling and Curie relaxation mechanisms. For the former the correlation time is the electron relaxation time itself and for the latter the rotational correlation time of the aqua ion. This is the first time that a Curie contribution to longitudinal relaxation has been observed through its magnetic field dependence. The electron relaxation times are confirmed to be magnetic field independent, very short, and substantially temperature independent. Their actual values are now proposed by taking into consideration crystal field effects. The mechanisms causing electron relaxation have been discussed.