Switching of magnetic and polarization characteristics in response to intramolecular ligand-metal electron transfer in dinuclear [FeCo] compounds.

A theoretical model has been developed to describe the spin transformation in the [(Fe(RR-cth))(Co(SS-cth))(μ-dhbq)](AsF6)3 compound, accompanied by a change in macroscopic polarization caused by electron density redistribution due to reversible intramolecular electron transfer between the μ-dhbq ligand and Fe ion. In this model, the states of a single complex arising from its three configurations are accounted: low-spin-Fe3+-dhbq3--low-spin-Co3+, high-spin-Fe3+-dhbq3--low-spin-Co3+ and high-spin-Fe2+-dhbq2--low-spin-Co3+. Due to the molecular structure of the compound demonstrating this transformation, the interaction between the molecular modes forming the spectrum of a single complex and the crystalline modes assuring cooperativity in the system is assumed to be responsible for the spin transformation. This model also includes the dipole-dipole interaction between complexes in the whole crystal responsible for electron density redistribution caused by electron transfer. The problem of interacting complexes is solved in the mean field approximation. On the basis of the developed model, a comprehensive explanation of the magnetic and polarization characteristics of the [(Fe(RR-cth))(Co(SS-cth))(μ-dhbq)](AsF6)3 compound is given. The inclusion of the intermediate excited configuration high-spin Fe3+-dhbq3--low-spin-Co3+, along with the ground and final configurations of the FeCo dimeric complex in the model, allows for the explanation of the unusual increase in the macroscopic polarization observed after the low-spin → high-spin transition in the iron ion is completed.