Influence of the Ligand Field on Slow Magnetization Relaxation versus Spin Crossover in Mononuclear Cobalt Complexes

摘要

One hundred years ago Alfred Werner won the Nobel Prize in chemistry for his pioneering work with inorganic coordination compounds, which was mainly attributed to his work on mononuclear cobalt complexes. Although this chemistry has been well-developed, in recent years it continues to reveal new and interesting magnetic properties derived from the molecular geometry of these complexes. Indeed since the discovery of magnet-like behavior in a mononuclear transition-metal complex, a sudden re-emergence of interest occurred in 3d molecules acting as molecular magnets. This is mainly due to the fact that these model mononuclear complexes can unravel the origin of magnetic anisotropy due to their unquenched first-order orbital angular momen-tum. When large uniaxial anisotropy (D) is coupled with the intrinsic spin (S) of a molecule, an anisotropic barrier (U=S~2 |D|) for the reversal of the magnetization can be seen.' Such molecules are termed single-molecule magnets (SMMs) or, for mononuclear complexes, single-ion magnets (SIMs). To compensate for low-spin values in 3d ions, highly anisotropic metal ions, such as Fe~(II) or Co~(II), are used.