Electron spin resonance study of manganese(II) dialkyl phosphates and diaryl phosphinates and phosphates

Abstract

E.s.r. spectra of manganese(II) complexes of dimethyl (dmp), diethyl (dep) and diphenyl (dϕp) phosphates and their derivatives show variations arising from subtle changes in both alkyl or aryl groups and associated solvent molecules. The X-band e.s.r. spectra can be divided into two groups. Spectra due to complexes of the type Mn[O₂P(OR)₂]₂, where R = Me or Et, range from 0 to 400 mT indicating that the crystal field splittings of the ground state of manganese(II) are comparable to the microwave absorption energy (i.e. either ∣2D∣ or ∣4D∣≈hν depending on the absolute sign of D). The second group of spectra is associated with the following complexes: Mn[O₂P(OR)₂]₂ L₂, where R = Me, Et, Ph and L = pyridine or R = Ph and L = dmf; Mn[O₂P(OPh)₂]₂, Mn[O₂PPh₂]₂ and Mn[O₂PPh₂]₂(dmf)₂. In this case, crystal field splittings are smaller than the microwave absorption energy and, from computer simulations of the spectra, estimates of the crystal field parameter, D, are obtained which lie in the range 0.012 to 0.0255 cm^–1. The rhombic symmetry component, E, was found to be almost zero.