Electron Paramagnetic Relaxation and EPR Line Shapes of Manganous Ion Complexes in Aqueous Solutions. Frequency and Ligand Dependence

Line shapes of electron paramagnetic resonance spectra of manganous ion in various ligand environments have been examined at two microwave frequencies, 9.1 and 35 GHz. From the observed differences in line shape at two microwave frequencies and the theoretical expression for relaxation of sextet state ions, the correlation times for processes modulating the zero‐field splitting (zfs) interaction and the magnitude of the effective zfs were evaluated. For all complexes which were examined the correlation times were in the range ${\text{3×10}}^{\text{−12}}{\text{−9×10}}^{\text{−12}}\sec$ at 300°K. Two types of zfs are distinguished, a transient zfs which is related to the relaxation processes and a static zfs. In this regard there appears to be no simple relation between the transient zfs as obtained from relaxation studies and the static zfs as obtained from solid‐state spectra. The large static zfs for MnEDTA gives quasi‐solid‐state features to the solution EPR spectra of this complex.