Temperature Independent Isotropic EPR Spectra of [(CH3)4N]2MnCl4 and [(CH3)4N]2FeCl4 Single Crystals

Electron paramagnetic resonance of [(CH3)4N]2MnCl4 and [(CH3)4N]2FeCl4 single crystals was studied between 20 and 400 K. The peak-to-peak derivative linewidths of these crystals seem not to change in this temperature interval and approximately 100 mT for [(CH3)4N]2MnCl4 and ~20 mT for [(CH3)4N]2FeCl4 .The spectra were found to be isotropic, with g = 2.0039 for [(CH3)4N]2MnCl4 and g = 2.0042 for [(CH3)4N]2FeCl4 .This temperature independence is attributed to isotropic strong ex-change interactions of Mn2- and Fe2+ nuclei, and it seems that hindered rotation of the MnCl42- and FeCl42- tetrahedra does not occur in this temperature interval.