Axial Ligand Field in D_4d Coordination Symmetry: Magnetic Relaxation of Dy SMMs Perturbed by Counteranions

Abstract

A series of mononuclear Dy complexes with the general formula [DyLz(salicylaldehyde)]·X·solvent (Lz = 6-pyridin-2-yl[1,3,5]triazine-2,4-diamine; X = OH (1·OH), Cl (2·Cl), Br (3·Br)) have been synthesized using mixed salicylaldehyde/pyridinyl-triazine ligands and discriminative counteranions. The Dy ion in these three complexes resides in a similar D coordination geometry with counteranions perturbing the coordination environment and bond lengths and angles in the lattice. Magnetostructural studies reveal that the asymmetric distribution of salicylaldehyde/pyridinyl-triazine ligands and the presence of discriminative counteranions result in the coexistence of large anisotropy and quantum tunneling of magnetization. The magnetic anisotropy is dominated by the axial ligand field with short Dy-O distances and large ∠O-Dy-O angles, while the quantum tunneling relaxation is probably dictated by the π-π stacking of the Lz ligands, which induces an axial constriction of the coordinating plane. Ab initio calculations substantiate the diversity of the magnetic behaviors in these complexes and highlight the importance of axial ligand field with short Dy-O distances, large ∠O-Dy-O angles and less ligand stacking in these pseudo-D-symmetrical single-molecule magnets.

Manipulating the Relaxation of Quasi-D4d Dysprosium Compounds through Alternation of the O-Donor Ligands

“…The ∠ O1-Dy-O2 angle o f 137.46° for 3Dy is smaller than 140.46° for perfect D 4d geometry. 30 The shortest intermolecular Dy•••Dy distance is 9.14 Å, here again suggesting the potential presence of intermolecular interactions. Magnetic properties.…”

“…Besides, the weak π•••π stacking between the ligands may introduce transversal components as a result of the change o f the electronic structure and coordination geometry. 30 Those two reasons mentioned above for complex 3Dy lead to the fast QTM at low-temperature regions. Theoretical analyses were performed in order to understand this difference.…”

Teaching an old molecule new tricks: evidence and rationalisation of the slow magnetisation dynamics in [DyTp2Acac]

“…This value is comparable to the reported energy splitting of the majority of Dy(III)-based SMM. 13,14,43,44 It is thus anticipated that [DyTp 2 Acac] may present a SMM behaviour. However one cannot be peremptory, as energy splitting is far from being the only parameter to master in order to induce a slow relaxation of magnetisation.…”

Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties

“…For Dy III ions with the oblate-shaped electron density, a crystal field in which the ligand electron density is concentrated above and below the equatorial plane is desired to enhance the magnetic anisotropy [19]. Furthermore, this kind of crystal field could lead to a highly efficient dysprosium SIM (single-ion magnet), such as D4d [20][21][22] or D5h [23][24][25]. Moreover, the low-coordinate lanthanide complexes are superior at controlling the coordinated environment and understanding the magnetostructural relationship [26][27][28][29][30].…”