Magnetic Anisotropy, Magneto–Structural Correlations and Mechanism of Magnetic Relaxation in {Dy III N 8 } Complexes: A Theoretical Perspective

Ab initio CASSCF calculations have been undertaken to probe the origin of magnetic anisotropy in two structurally related {Dy III N 8 } SIMs {[Dy(tmtaa) 2 ] – and [K(DME) 2 ][Dy(tmtaa) 2 ]; 1 and 2 , respectively}. Our calculations reveal that complex 1 possesses a larger barrier for reorientation of magnetization ( U cal ) than does 2 . This is essentially due to the intrusion of K + ions, which distort the geometry and the donor abilities of the ligands in complex 2 , compared with 1 . Moreover, the ligand field around Dy III was found to stabilize |m J > = |±13/2> as the ground state, with stronger mixing by other |m J > levels. This corresponds to the observation of large g xx and g yy values at the ground state, leading to an efficient QTM process and very fast relaxation. The computed ground‐state |m J > levels and the estimated g tensors for both complexes are in agreement with experimental results obtained from magnetic and EPR spectroscopic studies. In addition, we have developed various magneto–structural correlations for complexes 1 and 2 , in order to understand how small structural distortions are likely to influence the magnetic anisotropy. These correlations offer clues to enhancing the barrier height for magnetization reversal in {Dy III N 8 } complexes.