A Family of Co(II)Co(III)3 Single-Ion Magnets with Zero-Field Slow Magnetic Relaxation: Fine Tuning of Energy Barrier by Remote Substituent and Counter Cation.

The synthesis, structures, and magnetic properties of a family of air-stable star-shaped Co(II)Co(III)3 complexes were investigated. These complexes contain only one paramagnetic Co(II) ion with the approximate D3 coordination environment in the center and three diamagnetic Co(III) ions in the peripheral. Magnetic studies show their slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion with approximate D3 symmetry in the center. Most importantly, it was demonstrated that the anisotropy energy barrier can be finely tuned by the periphery substituent of the ligand and the countercation. The anisotropy energy barrier can be increased significantly from 38 K to 147 K.