Paramagnetic Resonance in some Complex Cyanides of the Iron Group II. Theory

Abstract

The theory of Stevens for covalent XY6 complexes is developed for the cases of d3 and d5 with low symmetry, and compared with the magnetic resonance results of the preceding paper. The effect of the coupling to the doublet states on the spin Hamiltonian constants for the d3 complexes is found to be small compared with that of coupling to the quartet states, although the latter are probably further removed energetically. In the d5 complexes it is shown that the relation between the g-values and the susceptibility does not depend on the orientation of the principal axes of the g tensor relative to the complex; the principal values of the susceptibility of K3Fe(CN)6 are calculated from the g-values and compared with earlier experimental determinations, the value of the spin-orbit coupling being adjusted to give the best fit. The observed hyperfine constants for K4Mn(CN)63H2O are compared with the theoretical expressions and can be explained with reasonable values of the parameters. The orbital g-factor k is found to be 0.87 for the ferricyanide and 0.74 for the manganocyanide. An appendix discusses the conditions under which hyperfine terms of low symmetry can appear in the spin Hamiltonian, and the effect they may have on the observed spectrum.