Spin-mixed States Research Articles

Spin-mixed states of ferric ion in complexes of tetragonal symmetry

Using a strong crystal field model for ferric ion complexes with tetragonal symmetry and allowing spin-orbit coupling between sextet, quartet, and doublet states, a mechanism is obtained whereby ferric ion can exist in four qualitatively different ground states: a sextet, a quartet, a doublet or a substantially spin-mixed state. We have delineated the regions in crystal field parameter space in which these various possible ground states prevail. Also, we have calculated the eigenfunctions and eigenvalues typical of each region. We discuss in detail the nature of the 5 lowest ferric ion functions in these different regions, particularly in the regions of spin-mixed states. With this model we obtain a picture of these various ferric ion states consistent with the behavior of known complexes of ferric ion, particularly of the ferric heme compounds. The results presented here will be used in a subsequent calculation of some of the observed properties of these compounds.

Spin-mixing and the different spin states of ferric ion in tetragonal symmetry

We have used the wave functions generated from a strong crystal field model of ferric ion in complexes of tetragonal symmetry with spin-orbit coupling, to calculate the behavior of several localized properties of the ferric ion in parameter regions of different ground and low-lying ferric ion states. In the previous paper of this series we have shown with this model that ferric ion can exist in a doublet, sextet, quartet and substantially spin-mixed ground state. We have delineated such regions and described the changing nature of the wave functions. In the present study, we calculate the effective magnetic moments and their temperature dependence, the first order magnetic field energies, and the electric field gradients of ferric ion in these various spin states. Particular emphasis is placed on the properties of ferric ion in substantially spin-mixed states which have hitherto not been reported. Wherever possible, our results are compared with existing experimental data. In particular, with this model, we have been able to quantitatively account for the continuously varying values of magnetic moment for a series of 12 ferric hemoglobin derivatives, in the region from range of 5.92 to 2.26 Bohr magnetons.