Magnetic Anisotropy, Magneto–Structural Correlations and Mechanism of Magnetic Relaxation in {Dy^IIIN₈} Complexes: A Theoretical Perspective

Abstract

Ab initio CASSCF calculations have been undertaken to probe the origin of magnetic anisotropy in two structurally related {DyIIIN8} 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 (Ucal) 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 DyIII was found to stabilize |mJ> = |±13/2> as the ground state, with stronger mixing by other |mJ> levels. This corresponds to the observation of large gxx and gyy values at the ground state, leading to an efficient QTM process and very fast relaxation. The computed ground‐state |mJ> 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 {DyIIIN8} complexes.

Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets

“…This is a consequence of large off-diagonal CF parameters (such as B 2 2 and B 4 2 ) and the large B 2 2 / B 2 0 ratio, which are caused by the substantial distortions of the Pc planes in M5 . Such distortions are shown in the large spread of D TbN nn , D TbC far , θ N nn TbN nn , and θ C far TbC far values (Table ), where the latter two quantities are similar to the twist angle parameter κ in ref . For M6 , the C 4 symmetry allows mixing of M J levels with Δ M J = ±4 only (Tables and S2 in the Supporting Information).…”

“…In order to characterize the experimental geometries, we introduce several structural parameters (Table and Figure ). Among them, the rotation between the ligands can be quantified by using two angles, θ N nn TbN nn and θ C far TbC far , which are similar to the twist angle κ used in ref . For M1 , M3 , and M6 molecules, both θ N nn TbN nn and θ C far TbC far are close to 45° which indicates that the fourfold symmetry is approximately preserved.…”

Boosting axiality in stable high-coordinate Dy(iii) single-molecule magnets

“…9 The Dy ion geometry is extremely important in order to obtain higher blocking temperatures and we reasoned that the combination of the pseudo D 4d {DyN 8 } cage with a strong axial ligand should show interesting SMM characteristics. 10 Herein, we report the synthesis, magnetic characterisation and ab initio studies of [Dy III LF](CF 3 SO 3 ) 2 ÁH 2 O (1). Furthermore, we demonstrate an elegant strategy for improving the magnetic behaviour of high-coordinate 4f complexes.…”

Importance of an Axial LnIII–F Bond across the Lanthanide Series and Single-Molecule Magnet Behavior in the Ce and Nd Analogues

“…To understand further the magnetic properties of these complexes and the role of the fluoride ligand in promoting strong axiality, we have prepared a series of computational models 1 -Ce(a), 3 -Nd(a), and 5 -Tb(a) where the axial F – ligand is removed, so that each model has just a {LnN 8 } coordination environment (see Figure S19 ). 74 The model structures were optimized using DFT calculations (see Experimental Methods ). For the 1 -Ce(a) and 3 -Nd(a) models, the calculations reveal smaller g zz values and larger g xx and g yy values, with the excited KDs closer in energy (see Table 7 ).…”