Theory of the isotropicgvalue of 4·27 found for some high-spin ferric ions

It has been suggested [4] that an isotropic g value of 4·27 given by the high-spin ferric ion occurs because D = 0, E ≠ 0 in a quadratic fine-structure spin-Hamiltonian. The plausibility of this interpretation is discussed and defended in the present paper. However, it is shown that D = 0, E ≠ 0 does not follow in any simple way from the symmetry of the environment, but probably arises through the effect of a ligand field on one of the excited 4 T 1 terms of the ferric ion. This is possible, providing the ligand field has a rather curious mixed symmetry. g values are given for the four doublets of S = 7/2 when D = 0, E ≠ 0; they do not even possess axial symmetry.