Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy₂ Single‐Molecule Magnets

Abstract

The utilization of 2-ethoxy-6-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol (H L) as a chelating ligand, in combination with the employment of alcohols (EtOH and MeOH) as auxiliary ligands, in 4 f-metal chemistry afforded two series of dinuclear lanthanide complexes of compositions [Ln L (NO ) (EtOH) ] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7)) and [Ln L (NO ) (MeOH) ] (Ln=Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Ho (13), Er (14)). The structures of 1-14 were determined by single-crystal X-ray crystallography. Complexes 1-7 are isomorphous. The two lanthanide(III) ions in 1-7 are doubly bridged by two deprotonated aminophenoxide oxygen atoms of two μ :η :η :η :η :η :η -L ligands. One nitrogen atom, two oxygen atoms of the NO anion, two methoxide oxygen atoms of two ligand sets, and one oxygen atom of the terminally coordinated EtOH molecule complete the distorted dodecahedron geometry of each lanthanide(III) ion. Compounds 8-14 are isomorphous and their structures are similar to those of 1-7. The slight difference between 1-7 and 8-14 stems from purposefully replacing the EtOH ligands in 1-7 with MeOH in 8-14. Direct-current magnetic susceptibility studies in the 2-300 K range reveal weak antiferromagnetic interactions for 3, 4, 7, 10, 11, and 14, and ferromagnetic interactions at low temperature for 5, 6, 12, and 13. Complexes 5 and 12 exhibit single-molecule magnet (SMM) behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12. The energy barrier is significantly enhanced by dexterously regulating the terminal ligands. To rationalize the observed difference in the magnetic behavior, complete-active-space self-consistent field (CASSCF) calculations were performed on two Dy complexes. Subtle variation in the angle between the magnetic axes and the vector connecting two dysprosium(III) ions results in a weaker influence on the tunneling gap of individual dysprosium(III) ions by the dipolar field in 12. This work proposes an efficient strategy for synthesizing Dy SMMs with high energy barriers.

Modulating the Magnetic Interaction in New Triple-Decker Dysprosium(III) Single-Molecule Magnets

“…Specifically, the angle (θ 2 ) of the anisotropy axis on Dy2 with Dy III ···Dy III linkage for 1 is only 14.6°, which is about half of that in 2 (30.2°). The smaller value in 1 leads to a weaker influence on the tunneling gap of the individual Dy III ion by the dipolar field and significantly reduces the efficiency of the tunneling relaxations. , In addition, according to the EPR studies of the Dy 2 complex from the van Slageren group, the magnetic interaction between anisotropic lanthanide centers is extremely sensitive to the arrangement of anisotropy axes . The drastic change in the arrangement of anisotropy axes most likely affects the overlap between dysprosium orbitals and valency orbitals of the bridging ligands, thus influencing the magnetic interactions in this system.…”

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature

“…The simplest one is the lanthanide (III) dinuclear SMM. The ferromagnetic coupling strategy may make the magnetic orientation of the two lanthanide (III) ions uniform, but it is still a very difficult task. − The main reason is that the 4f electrons from different lanthanide (III) ions are not easily magnetically exchanged with each other; even if this magnetic exchange occurs, it is usually a weak antiferromagnetic interaction.…”

Single‐Molecule Magnetism in Dy2 Cluster Based on a Schiff Base Ligand

“…Although complex 1 joins a big family of Dy 2 clusters, [ 11–40 ] none of the complexes crystallized from the DME solution, and the DME oxygen atom also serves as a coordination site in 1 . These features indicate the improvement of the synthesis method and the structural novelty of complexes 1 and 2 .…”

“…[ 4–10 ] Among all the lanthanide‐based SMMs, [Ln 2 ]SMMs have attracted significant attention of the chemists and physicists in the world. [ 11–40 ] There are many reasons for this, for example, (i) compared with other polynuclear clusters, the synthesis of [Ln 2 ] is easier to control; (ii) the structure‐property relationships of the dinuclear systems could be easily investigated by modifying the functional groups of the ligands; (iii) in studying the magnetic interaction between two lanthanide atoms, they represent the simplest structural units; and (iv) it is relatively convenient to determine the possible orientation of anisotropy in the dinuclear system. We believe that Ln 2 is the most basic structure in explaining the nature of single molecule magnets (such as the relationship between single ion relaxation and molecular entity relaxation; the influence of magnetic interaction on magnetization relaxation, the possible orientation of anisotropy).…”