Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single‐Molecule‐Magnet Nodes within a Metal–Organic Framework

Pressure-Induced Structural, Optical and Magnetic Modifications in Lanthanide Single-Molecule Magnets

Lanthanide Single-Molecule Magnets are fascinating objects that break magnetic performance records with observable magnetic bistability at the boiling temperature of liquid nitrogen, paving the way for potential applications in high-density data storage. The switching of lanthanide SMM has been successfully achieved using several external stimuli such as redox reaction, pH titration, light irradiation or solvation/desolvation thanks to the high sensitivity of the magnetic anisotropy to any structural change in the lanthanide surrounding. Nevertheless, the use of applied high pressure as an external stimulus is largely underused, especially considering that it can be combined with high pressure X-ray diffraction to establish a complementary structure-property relationship. This Concept article summarizes the few relevant examples of investigations of lanthanide SMMs under applied high pressure, provides conclusions on the effect of such stimulus on molecular structures and magnetic anisotropy, and finally draws perspective on the future development of magnetic measurements under applied pressure.

X-Ray Triggered Coordination-Bond Breakage in Dysprosium-Organic Framework and its Impact on Magnetic Properties

Photosensitive lanthanide-based single-molecule magnets (Ln-SMM) are very attractive for their potential applications in information storage, switching, and sensors. However, the light-driven structural transformation in Ln-SMMs hardly changes the coordination number of the lanthanide ion. Herein, for the first time it is reported that X-ray (λ=0.71073 Å) irradiation can break the coordination bond of Dy-OH₂ in the three-dimensional (3D) metal-organic framework Dy₂ (amp₂ H₂ )₃ (H₂ O)₆  ⋅ 4H₂ O (MDAF-5), in which the {Dy₂ (OPO)₂ } dimers are cross-linked by dianthracene-phosphonate ligands. The structural transformation proceeds in a single-crystal-to-single-crystal (SC-SC) fashion, forming the new phase Dy₂ (amp₂ H₂ )₃ (H₂ O)₄  ⋅ 4H₂ O (MDAF-5-X). The phase transition is accompanied by a significant change in magnetic properties due to the alteration in coordination geometry of the Dy^III ion from a distorted pentagonal bipyramid in MDAF-5 to a distorted octahedron in MDAF-5-X.

An Azido-Bridged Dysprosium Chain Complex Showing Zero-field Slow Magnetic Relaxation

A one-dimensional (1D) azido-bridged dysprosium coordination polymer featuring a zig-zag chain structure constructed from a halogen-functionalized quinoline derivative and N₃ ^- ligands was structurally and magnetically characterized. Magnetic studies revealed that the chain complex exhibits zero-field slow magnetic relaxation and a significant butterfly-like hysteresis loop, originating from highly magnetic anisotropy of the Dy³⁺ ions in a D_4d symmetry. This compound represents the first azido-bridged lanthanide chain showing zero-field slow magnetic relaxation behavior. These results highlight that the combination of high symmetric Ln³⁺ ions with the versatile azido bridging ligand provides an effective approach for the design and construction of advanced lanthanides molecular magnets.

Solvato Modulation of the Magnetic Memory in Isotopically Enriched Erbium Polyoxometalate

Single-Molecule Magnet (SMM) property is by essence molecular, while commonly measured in solid crystalline state. Solvent crystallization molecules are usually neglected in the analysis and interpretation of solid-state properties. The solvation/desolvation process in the polyoxometalate(POM)-based Na₉ [Er(W₅ O₁₈ )₂ ] ⋅ 35 H₂ O SMM demonstrates that the dehydrated form relaxes more than 1000 times faster than the initial state, while the rehydration process allows the quasi complete recovering of the initial magnetic behaviour. This dehydration process is monitored by thermogravimetric analysis (TGA) and temperature-dependent X-ray powder diffraction, and rationalized by periodic quantum chemical calculations evidencing the tremendous role of the labile water molecules in the stability of the edifice. Ab-initio calculations highlight that sodium ions localization in the structure drive the magnetic responses. Isotopic enrichment with nuclear spin free (¹⁶⁶ Er, I=0) Er^III ions shows that the relaxation dynamics in the quantum regime depends on the nuclear spin.

Rare-Earth Metal Tetrathiafulvalene Carboxylate Frameworks as Redox-Switchable Single-Molecule Magnets

Using the redox-active tetrathiafulvalene tetrabenzoate (TTFTB^4- ) as the linker, a series of stable and porous rare-earth metal-organic frameworks (RE-MOFs), [RE₉ (μ₃ -OH)₁₃ (μ₃ -O)(H₂ O)₉ (TTFTB)₃ ] (1-RE, where RE=Y, Sm, Gd, Tb, Dy, Ho, and Er) were constructed. The RE₉ (μ₃ -OH)₁₃ (μ₃ -O) (H₂ O)₉ ](CO₂ )₁₂ clusters within 1-RE act as segregated single-molecule magnets (SMMs) displaying slow relaxation. Interestingly, upon oxidation by I₂ , the S=0 TTFTB^4- linkers of 1-RE were converted into S= 1 / 2 TTFTB^.3- radical linkers which introduced exchange-coupling between SMMs and modulated the relaxation. Furthermore, the SMM property can be restored by reduction in N,N-dimethylformamide. These results highlight the advantage of MOFs in the construction of redox-switchable SMMs.

All-Inorganic Single-Ion Magnets in Ceramic Matrices

All-inorganic single-ion magnets representing paramagnetic ions incorporated in a crystalline diamagnetic matrix are reviewed. Key results and advantages of this approach in comparison with the common strategy based on molecular metal-organic complexes are considered, and some unsolved problems and future perspectives are discussed.

Remarkable Energy Barrier for Magnetization Reversal in 3D and 2D Dysprosium-Chloranilate-Based Coordination Polymers

Herein, two coordination polymers (CPs) [{Dy(Cl₂ An)_1.5 (CH₃ OH)}⋅4.5 H₂ O]_n (1) and [Dy(Cl₂ An)_1.5 (DMF)₂ ]_n (2), in which Cl₂ An is chloranilate (2,5-dihydroxy-1,4-benzoquinone dianion), exhibiting field-induced single-molecule magnet behavior with moderate barrier of magnetization reversal are reported. Detailed structural and topological analysis disclosed that 1 has a 3D network, whereas 2 has a 2D layered-type structure. In both CPs, magnetic measurements showed weak antiferromagnetic exchange interaction between the dysprosium centers and field-induced slow magnetic relaxation with barriers of 175(9)K and 145(7)K for 1 and 2, respectively. Notably, the energy barriers of magnetization reversal of 1 and 2 are remarkable for metal-chloranilate-based 3D (1) and 2D (2) CPs. The temperature and field dependence of relaxation time indicate the presence of multiple relaxation pathways, such as direct, quantum tunneling of magnetization, Raman, and Orbach processes, in both CPs. Ab initio theoretical calculations reinforced the experimentally observed higher energy barrier in 1 as compared with 2 due to the presence of large transverse anisotropy in the ground state in the latter. The average transition magnetic moment between the computed low-lying spin-orbit states also rationalized the relaxation as Orbach and Raman processes through the first excited state. BS-DFT calculations were carried out for both CPs to provide more insight into the exchange interaction.

Synthesis, Structures, and Single-Molecule Magnetic Properties of Three Dy2 Complexes

To explore the influences of the subtle structural variations in the ligand backbones on the single-molecule magnetic properties of dinuclear dysprosium(III) complexes, three ligands-H₂ L₁ (H₂ L₁ =N₁ ,N₃ -bis(salicylaldehyde)diethylenetriamine), H₂ L₂ (H₂ L₂ =N₁ ,N₃ -bis(3-methoxysalicylidene)diethylenetriamine), and H₂ L₃ (H₂ L₃ =N₁ ,N₃ -bis(5-chlorosalicyladehyde)diethylenetriamine)-were synthesized and employed to prepare the expected dinuclear dysprosium(III) complexes. The three ligands differ in terms of the substituents at the benzene rings of the salicylaldehyde moieties. The reactions of Dy(NO₃ )₃ ⋅6 H₂ O, pivalic acid, and the ligands H₂ L₁ , H₂ L₂ , and H₂ L₃ generated complexes with the formulae [Dy₂ (L₁ )₂ (piv)₂ ] (1), [Dy₂ (L₂ )₂ (piv)₂ ] (2), and [Dy₂ (L₃ )₂ (piv)₂ ]⋅ 2 MeCN (3), respectively. The purposeful attachment of the functional groups with varied sizes at the benzene rings of the salicylaldehyde backbones resulted in slight differences in the Dy-O-Dy bond angles and the Dy⋅⋅⋅Dy bond lengths in 1-3; consequently, the three complexes exhibited distinct magnetic properties. They all showed slow magnetization relaxation with energy barriers of 40.32 (1), 31.67 (2), and 33.53 K (3). Complete active space self-consistent field (CASSCF) calculations were performed on complexes 1-3 to rationalize the slight discrepancy observed in the magnetic behavior. The calculated results satisfactorily explained the experimental outcomes.

Towards solvent tuning of slow magnetic relaxation and ferroelectric properties in a dysprosium metal–organic framework system

A new dysprosium metal–organic framework {[Dy2(L)3(H2O)4]·(acetone)2·(H2O)3} n (Dy2-Acetone) with single-molecule magnet and ferroelectric properties was synthesized through a solvent-induced single-crystal-to-single-crystal (SCSC) transformation. Notably, exchange of the coordinated and guest solvent molecules lead to different magnetic relaxation and ferroelectric properties in the dysprosium MOF system, Dy2-DMF and Dy2-Acetone. Study reveals that the tunable magnetic relaxation behaviors are most likely a result of different local coordination sphere and lattice solvent molecules within the pores which influenced and tuned the relaxation rates of the magnetization. Moreover, disparate polar solvent molecules confined in the MOFs may be the key factors for their different ferroelectric properties.

Conducting Molecular Nanomagnet of DyIII with Partially Charged TCNQ Radicals

Bifunctional electrically conducting single-molecule magnets are highly promising platforms for non-volatile memory devices and quantum computing applications. The development of these molecular materials, however, has largely been hindered by the lack of straightforward synthetic methods. Herein a facile and modular approach is demonstrated for the realization of bifunctional materials that does not require electrochemical or chemical oxidation to obtain partially charged organic radicals. Magnetic and electrical conductivity studies reveal that the Dy^III compound exhibits slow relaxation of the magnetization between 5.0-8.0 K and semiconducting behavior over the range 180-350 K. DC magnetic fields have been found to suppress the quantum tunneling of the magnetization and affect the spin-canted antiferromagnetic interactions.