Electron Paramagnetic Resonance Spectra have been recorded for some compounds of the type Mn(ligand)4- (anion)2, with pyrazole and 3(5)-methyl pyrazole as the ligands, and Cl−, Br−, I−, and NO3−, as the anions. The spectra show absorptions far from geff=2 for all compounds at both X- and Q-band frequencies. these spectra can be interpreted on the basis of a slightly distorted D4h symmetry for S=5/2, with D= 0.05–1.5 cm−1 and λ (being equal to E/D)=0.01–0.1 The different values of the parameters for the several compounds can be explained by differences in the axial ligand-field strengths.
Dowsing, R. D., Nieuwenhuijse, B., & Reedijk, J. (1971). Pyrazoles and imidazoles as ligands. X. electron paramagnetic resonance spectra of MnII in a tetragonal environment of four pyrazoles and two anions. Inorganica chimica acta, 5, 301-304. https://doi.org/10.1016/S0020-1693(00)95933-4