An EPR study of some highly distorted tetrahedral manganese(II) complexes at high magnetic fields

EPR spectra at 94.5 GHz (3 mm) and 249.9 GHz (1 mm) have been measured for the dichloro-, dibromo-, and diiodobis(triphenylphosphine oxide)manganese(I I) complexes. These compounds have a distorted tetrahedral geometry, and th e highest possible symmetry obtainable is Cr,. Because the spectra are take n in the high-field limit, they are simple and much easier to interpret tha n at lower magnetic fields. Accurate values of the zero-field splitting par ameters, D and eta (E/D), are determined by least-squares fitting and homot opy using matrix diagonalization. The compounds have g-values near 2 and la rge values of D and eta. Across the series, D increases from 0.165 to 0.906 cm(-1), while eta decreases slightly from 0.273 to 0.246.