Second-Shell Effects on the Magnetic Anisotropy of Tetracoordinate Heteroleptic Co(II) Complexes.

Magnetic anisotropy in a series of mononuclear Co(II) complexes featuring a distorted tetrahedral S2N2 coordination environment was investigated using a combination of ab initio calculations and complementary experimental techniques. The results of ab initio calculations are supported by experimentally obtained d-d transition energies and data from dc magnetization and EPR spectroscopy. Computational studies of magnetostructural relationships on the modeled structure show how, in heteroleptic complexes containing π-interacting ligands, the second-shell atoms-those directly connected to the donor atoms-influence the magnetic anisotropy. In particular, it was shown that in such complexes, switching between different types of magnetic anisotropy (easy-axis, easy-plane, triaxial) as well as between orientations of the easy-magnetized axis/plane can be achieved by modifying factors related solely to the spatial arrangement of second-shell atoms. The computational results are analyzed in detail to elucidate how the combined effects of the first ligand shell and second-shell geometry modulate the Zero-Field Splitting parameters of tetracoordinate heteroleptic Co(II) complexes.