Intramolecular Ferromagnetism in Di-Nuclear 3 d-Transition-Metal Single-Molecule Magnets by Pseudo-Serial Arrangement

Di-nuclear citrate complexes, [CH₆ N₃ ]₂ [M₂ (citH)₂ (H₂ O)₄ ] ⋅ 2H₂ O (citH₄ =citric acid; M=Fe^II (Fe-2), Co^II (Co-2), and Ni^II (Ni-2)), are synthesized. The ligand, citH^3- , is deprotonated only at the three carboxy groups, which is different from the previously reported tetra-nuclear structures with cit^4- ligands. Magnetic measurements reveal that these complexes have intramolecular ferromagnetism with J=∼0 cm^-1 (Ni-2), 0.02 cm^-1 (Co-2), and 0.04 cm^-1 (Fe-2). Co-2 and Fe-2 show slow magnetic relaxation, and are field-induced SMMs with activation energy of spin-reversal U_eff =27 cm^-1 (Co-2) and 4.2 cm^-1 (Fe-2). Density functional theory calculations indicate that the uniaxial anisotropy along the z-axis of each metal ion center forms the pseudo-serial arrangement, leading to intramolecular ferromagnetism via the magnetic dipole interaction. This work demonstrates the creation of ferromagnetic SMMs by the magnetic dipole engineering of 3d di-nuclear metal ion centers.

Lanthanide Single-molecule Magnets: Synthetic Strategy, Structures, Properties and Recent Advances

Single-molecule magnets (SMMs) show wide potential applications in the field of ultrahigh-density storage materials, quantum computing, spintronics, and so on. Lanthanide (Ln) SMMs, as an important category of SMMs, open up a promising prospect due to their large magnetic moments and huge magnetic anisotropy. However, the construction of high performance for Ln SMMs remains an enormous challenge. Although remarkable advances are focused on the topic of Ln SMMs, the research on Ln SMMs with different nuclear numbers is still deficient. Therefore, this review summarizes the design strategies for the construction of Ln SMMs, as well as the metal skeleton types. Furthermore, we collect reported Ln SMMs with mononuclearity, dinuclearity, and multinuclearity (three or more Ln spin centers) and the SMM properties including energy barrier (U_eff ) and pre-exponential factor (τ₀ ) are described. Finally, Ln SMMs with low-nuclearity SMMs, especially for single-ion magnets (SIMs), are highlighted to understand the correlations between structures and magnetic behavior of the detail SMM properties are described. We expect the review can shed light on the future developments of high-performance Ln SMMs.

Manipulation of the Coordination Geometry along the C4 Rotation Axis in a Dinuclear Tb3+ Triple-Decker Complex via a Supramolecular Approach

A supramolecular complex (1⋅C₆₀ ) was prepared by assembling (C60-Ih)[5,6]fullerene (C₆₀ ) with the dinuclear Tb³⁺ triple-decker complex [(TPP)Tb(Pc)Tb(TPP)] (1: Tb³⁺ =trivalent terbium ion, Pc^2- =phthalocyaninato, TPP^2- =tetraphenylporphyrinato) with quasi-D_4h symmetry to investigate the relationship between the coordination symmetry and single-molecule magnet (SMM) properties. Tb³⁺ -Pc triple-decker complexes (Tb₂ Pc₃ ) have an important advantage over Tb³⁺ -Pc double-decker complexes (TbPc₂ ) since the magnetic relaxation processes correspond to the Zeeman splitting when there are two 4f spin systems. The two Tb³⁺ sites of 1 are equivalent, and the twist angle (φ) was determined to be 3.62°. On the other hand, the two Tb³⁺ sites of 1⋅C₆₀ are not equivalent. The φ values for sites Tb1 and Tb2 were determined to be 3.67° and 33.8°, respectively, due to a change in the coordination symmetry of 1 upon association with C₆₀ . At 1.8 K, 1 and 1⋅C₆₀ undergo different magnetic relaxations, and the changes in the ground state affect the spin dynamics. Although 1 and 1⋅C₆₀ relax via QTM in a zero applied magnetic field (H), H dependencies of the magnetic relaxation times (τ) for H>1500 Oe are similar. On the other hand, for H<1500 Oe, the τ values have different behaviors since the off-diagonal terms ( B k q ; q ≠ 0 ) affect the magnetic relaxation mechanism. From temperature (T) and H dependences of τ, spin-phonon interactions along with direct and Raman mechanisms explain the spin dynamics. We believe that a supramolecular method can be used to control the magnetic anisotropy along the C₄ rotation axis and the spin dynamic properties in dinuclear Ln³⁺ -Pc multiple-decker complexes.

Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Single-Ion Magnets

Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph3 SiO- (Ph3 SiO- =anion of triphenylsilanol) and the 2,4-di-t Bu-PhO- (2,4-di-t Bu-PhO- =anion of 2,4-di-tertbutylphenol) ligands combined with the weak equatorial field of the ligand LN6 , leads to [DyIII (LN6 )(2,4-di-t Bu-PhO)2 ](PF6 ) (1), [DyIII (LN6 )(Ph3 SiO)2 ](PF6 ) (2) and [DyIII (LN6 )(Ph3 SiO)2 ](BPh4 ) (3) hexagonal bipyramidal dysprosium(III) single-molecule magnets (SMMs) with high anisotropy barriers of Ueff =973 K for 1, Ueff =1080 K for 2 and Ueff =1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher-order symmetry SMMs.

Solvent-tuned magnetic exchange interactions in Dy2 systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)]₂ (1), [Dy(api)]₂·2CH₂Cl₂ (2), [Dy(Clapi)]₂·2C₄H₈O (3), and [Dy(Clapi)]₂·2C₃H₆O (4) (H₃api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H₃Clapi = 2-(2′-hydroxy-5′-chlorophenyl)-1,3-bis[3′-aza-4′-(2′′-hydroxy-5′′-chlorophenyl)prop-4′-en-1′-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H₃api/H₃Clapi with DyCl₃·6H₂O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N₄O₃) to encapsulate a Dy^III ion and all of the Dy^III centers in 1–4 adopt a distorted square antiprism geometry with D_4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2–4 showed filed-induced slow magnetic relaxation with barriers U_eff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1–4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the Dy^III ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the U_eff values. The different lattice solvents influence Dy–O–Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.

Solvent-tuning changes the magnetic exchange interaction and results in different magnetic relaxation dynamics in Dy₂ systems ligated by a μ-phenolato heptadentate Schiff base.