Recent advances in dysprosium-based single molecule magnets: Structural overview and synthetic strategies

Correlation between Slow Magnetic Relaxations and Molecular Structures of Dy(III) Complexes with N5O4 Nona-Coordination

A series of Dy(III) mononuclear complexes [DyA2L]+ (L denotes Schiff base N5 ligand that occupies equatorial positions and A− denotes bidentate anionic O-donor ligands such as NO3− (1), AcO− (2), and acac− (3)) were synthesized to investigate the correlation between the slow magnetic relaxation phenomena and the coordination structures around Dy(III). The Dy(III) ion in each complex is in a nona-coordination with the anionic O-donor ligand occupying up- and down-side positions of the N5 equatorial plane. 2 and 3 show slow magnetic relaxation phenomena under a zero bias-field condition, and all complexes showed slow magnetic relaxation under the applied 1000-Oe bias-field conditions. Arrhenius analyses revealed that the ΔE/kB, the barrier height for magnetization flipping, increases in this order, with the values of 24.1(6), 85(3), and 140(15) K. The effects of the exchanging axial ligands on the magnetic anisotropy were discussed together with the DFT calculations.

Lanthanide anthracene complexes: slow magnetic relaxation and luminescence in DyIII, ErIII and YbIII based materials

Four mononuclear lanthanide complexes, [Ln(depma)2(H2O)6]Cl3·xH2O·yCH3OH [Ln = Dy (1Dy), x = 6, y = 0; Gd (2Gd), x = 3, y = 1; Er (3Er), x = 6, y = 0; Yb (4Yb), x = 3, y = 1; depma = 9-diethylphosphono-methylanthracene], are reported and structurally characterized. The octa-coordinated environment of LnIII is composed of two oxygen atoms from two different depma ligands and six oxygen atoms from each bound water molecule. All four complexes show photoluminescence in the solid state at room temperature, originating from the ligand-centered emissions of depma. Furthermore, slow magnetization relaxation is found in 1Dy, 3Er and 4Yb with the energy barriers (Ueff) of 40.5 K (1 kOe), 9.8 K (1 kOe) and 28.9 K (0.75 kOe), respectively.

Recent advances in single molecule magnetism of dysprosium-metallofullerenes

This article outlines the magnetic properties of single molecule magnets based on Dy-encapsulating endohedral metallofullerenes. The factors that govern these properties, such as the influence of different non-metal species in clusterfullerenes, the cage size, and cage isomerism are discussed, as well as the recent successful isolation of dimetallofullerenes with unprecedented magnetic properties. Finally, recent advances towards the organization of endohedral metallofullerenes in 1D, 2D, and 3D ordered structures with potential for devices are reviewed.

Determination of the electronic structure of a dinuclear dysprosium single molecule magnet without symmetry idealization

We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet [Dy2(bpm)(fod)6] (Hfod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine). Ab initio calculations were used to obtain a global picture of the electronic structure and to predict possible single molecule magnet behaviour, confirmed by experiments. The orientation of the susceptibility tensor was determined by means of cantilever torque magnetometry. An experimental determination of the electronic structure of the lanthanide ion was obtained combining Luminescence, Far Infrared and Magnetic Circular Dichroism spectroscopies. Fitting these energies to the full single ion plus crystal field Hamiltonian allowed determination of the eigenstates and crystal field parameters of a lanthanide complex without symmetry idealization. We then discuss the impact of a stepwise symmetry idealization on the modelling of the experimental data. This result is particularly important in view of the misleading outcomes that are often obtained when the symmetry of lanthanide complexes is idealized.

Tetranuclear dysprosium single-molecule magnets: tunable magnetic interactions and magnetization dynamics through modifying coordination number

The study of mononuclear lanthanide-based systems, where the observed Single Molecule Magnets (SMMs) properties originate from the local magnetic anisotropy of the single lanthanide ion, has been extensively investigated in the literature. The case for polynuclear lanthanide SMMs becomes more challenging both experimentally and theoretically due to the complexity of such architectures involving interactions between the magnetic centers. Much interest was devoted to the study of the structural effect on the magnetic interactions and relaxation dynamics. However, the understanding of the structural influence on those two factors remains a difficult task. To address this issue, a system containing two structurally related tetranuclear Dy(iii) SMMs, namely [Dy4(L)4(OH)2(DMF)4(NO3)2]·2(DMF)·(H2O) (1) and [Dy4(L)4(OH)2(DMF)2(NO3)2] (2) (H2L = 2-(2-hydroxy-3-methoxybenzylideneamino)phenol), is introduced and investigated. Through modifying the ligands on the changeable coordination sites, the intramolecular magnetic interactions and relaxation dynamics in these two Dy(iii)4 SMMs can be tuned. Both complexes exhibit slow relaxation of their magnetization with a relaxation barrier of 114 K for complex 2 while a blocking temperature below 2 K is observed for complex 1. Ab initio calculations reveal that changes in coordination numbers and geometries on the Dy(iii) sites can significantly affect the magnetic interactions as well as single-ion anisotropy. The combination of experimental work and ab initio calculations offers insight into the relationship between structures and magnetic properties and sheds light on the rational design of future polynuclear lanthanide SMMs with enhanced magnetic properties.

Single Crystal Investigations Unravel the Magnetic Anisotropy of the "Square-In Square" Cr4Dy4 SMM Coordination Cluster

In the search for new single molecule magnets (SMM), i.e., molecular systems that can retain their magnetization without the need to apply an external magnetic field, a successful strategy is to associate 3d and 4f ions to form molecular coordination clusters. In order to efficiently design such systems, it is necessary to chemically project both the magnetic building blocks and the resultant interaction before the synthesis. Lanthanide ions can provide the required easy axis magnetic anisotropy that hampers magnetization reversal. In the rare examples of 3d/4f SMMs containing Cr^III ions, the latter turn out to act as quasi-isotropic anchors which can also interact via 3d-4f coupling to neighbouring Ln centres. This has been demonstrated in cases where the intramolecular exchange interactions mediated by Cr^III ions effectively reduce the efficiency of tunnelling without applied magnetic field. However, describing such high nuclearity systems remains challenging, from both experimental and theoretical perspectives, because the overall behaviour of the molecular cluster is heavily affected by the orientation of the individual anisotropy axes. These are in general non-collinear to each other. In this article, we combine single crystal SQUID and torque magnetometry studies of the octanuclear [Cr₄Dy₄(μ₃-OH)₄(μ-N₃)₄(mdea)₄(piv)₈]·3CH₂Cl₂ single molecule magnet (piv=pivalate and mdea=N-methyldiethanol amine). These experiments allowed us to probe the magnetic anisotropy of this complex which displays slow magnetization dynamics due to the peculiar arrangement of the easy-axis anisotropy on the Dy sites. New ab initio calculations considering the entire cluster are in agreement with our experimental results.

Heterometallic grids: synthetic strategies and recent advances

Supramolecular metallogrid complexes are metalloclusters involving metal ions in planar array arrangements and organic ligands in perpendicular arrangements at each corner of the metal sites. Such essentially metal ion arrays have attracted great attention in the last three decades owing to their variety of interesting optical, electronic and magnetic properties. Among them, metallogrids containing more than one type of metal, that is heterometallic grids, are rare but have more potential to engineer a higher level functionality into one molecule. However, until now, only dozens of heterometallic grids have been reported without any specific review. Herein, we aim to give an overview of the assembly strategies, the physicochemical properties, and finally some perspectives on the future development of heterometallic grids.

A new family of dinuclear lanthanide complexes constructed from an 8-hydroxyquinoline Schiff base and β-diketone: magnetic properties and near-infrared luminescence

Six phenoxo-O bridged dinuclear lanthanide(iii) complexes have been assembled utilizing the 2-[(4-nitrophenyl)imino]methyl-8-hydroxyquinoline (HL) and dibenzoylmethane (Hdbm) ligands: [Ln2(dbm)4L2] (Ln = Nd (1), Eu (2), Gd (3), Tb (4), Dy (5) and Er (6)). Complexes 1 and 6 exhibit the characteristic emission peaks of the corresponding Nd3+ and Er3+ ions, respectively. Meanwhile, the excitation wavelength (470 nm) for complex 1 is located in the visible-light region, confirming a practical application value. The studies on magnetic properties reveal that complex 3 features a magnetocaloric effect with a magnetic entropy change of -ΔSm = 14.36 J kg-1 K-1 at 4 K for ΔH = 7 T. What's more, the dynamic magnetic studies for complex 5 show that it exhibits slow magnetic relaxation behavior, typical of SMM behavior, resulting in an energy barrier of ΔE/kB = 75 K with the pre-exponential factor τ0 = 2.2 × 10-7 s. Meanwhile, this research demonstrates that the magnetic properties can be modulated by regulating the electron-donating/withdrawing effects of the substituents on the ligands.

A series of [2 × 2] square grid LnIII4 clusters: a large magnetocaloric effect and single-molecule-magnet behavior

Four new [2 × 2] square grid LnIII4 clusters were successfully synthesized by employing a multidentate chelating Schiff base ligand. Magnetic studies showed that cluster 1 displays a larger magnetocaloric effect (−ΔS_m = 34.46 J kg⁻¹ K⁻¹ for ΔH = 7.0 T at 2.0 K), while 3 exhibits slow relaxation behavior under a zero dc field, with ΔE/k_B of 42.76 K and τ₀ of 1.02 × 10⁻⁶ s.

A decanuclear [DyIII6ZnII4] cluster: a {ZnII4} rectangle surrounding an octahedral {DyIII6} single molecule magnet

The synthesis, structure and magnetic relaxation properties of a decanuclear [DyIII6ZnII4] complex are reported.

Dinuclear lanthanide–lithium complexes based on fluorinated β-diketonate with acetal group: magnetism and effect of crystal packing on mechanoluminescence

A convenient and straightforward synthesis of a novel type of Ln–Li β-diketonates with a discrete molecular structure is presented.

Single molecule magnet behavior and magnetic refrigeration of four tetranuclear lanthanide (Ln = GdIII, TbIII, DyIII) clusters

Four lanthanide complexes were fabricated and characterized. 1 and 4 exhibit a cryogenic magnetic refrigeration property and 3 displays slow relaxation of magnetization.

Controllable syntheses and magnetic properties of novel homoleptic triple-decker lanthanide complexes

A class of novel triple-decker lanthanide complexes have been continuously designed and synthesized based on a Schiff base ligand Cl-salphenH₂ and precursors [(acac)₄Ln₂(L)]. The results reveal Dy complex behaves as a typical SMM with intermetallic ferromagnetic interaction.

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.

Design principle of half-sandwich type erbium single-ion magnets through crystal field engineering: a combined magnetic and electronic structure study

In this work, we demonstrated the design principle for high-performance erbium-based single-ion magnets (SIMs) by comparing two half-sandwich type erbium complexes.

Metal–organic frameworks based on polynuclear lanthanide complexes and octahedral rhenium clusters

A series of MOFs comprising tetrahedral lanthanide complexes, isonicotinate linkers, and the octahedral cluster anion [Re₆S₈(CN)₆]^4– demonstrate structure-directing effects of the rhenium cluster.

Hyperfine coupling and slow magnetic relaxation in isotopically enriched DyIII mononuclear single-molecule magnets

On the role of hyperfine coupling constant on the relaxation time of single-molecule magnets.

Magnetic investigations over reversibly switched chiral (phthalocyaninato)(porphyrinato) dysprosium double-decker compounds

The present work represents one example of reversibly tuning the molecular magnetic properties of Ln-based compounds and elucidates an abnormal f-radical effect.

The effect of the second coordination sphere on the magnetism of [Ln(NO3)3(H2O)3]·(18-crown-6) (Ln = Dy and Er)

The objective of this work was the exploration of the effect of the second coordination sphere on the magnetic properties of [Ln(NO₃)₃(H₂O)₃]·(18C6) (Ln = Dy (1) and Er (2)) compounds comprising co-crystallized 18-crown-6 ethers. Both compounds were identified as field-induced single molecule magnets (SMMs) with estimated magnetization reversal barriers U_eff = 66–71 K for 1 and U_eff = 21–24 K for 2. Theoretical calculations with the B3LYP functional revealed substantial change and redistribution of the electrostatic potential upon accounting for the second coordination sphere represented by two 18C6 molecules, which resulted in the change of the crystal-field around metal atoms. As a result, the multireference CASSCF calculations exposed significant impact of the second coordination sphere on the energy splitting of the respective ⁶H_15/2 (Dy^III) and ⁴I_15/2 (Er^III) ground states, the magnetization reversal barrier and the magnetic anisotropy parameters. Moreover, the calculated magnetization reversal barriers, U_calc. = 57 K for 1 and U_calc. = 16 K for 2, are in good agreement with the experimental values accentuating the importance of the second coordination sphere on the magnetic properties of SMMs.

The impact of the second coordination sphere on the magnetic properties of [Ln(NO₃)₃(H₂O)₃]·(18C6) compounds comprising co-crystallized 18-crown-6 ethers was investigated.

Synthesis, crystal structures and magnetic properties of a series of pentanuclear heterometallic [CuII3LnIII2] (Ln = Ho, Dy, and Gd) complexes containing mixed organic ligands

Three novel heterometallic compounds [CuII3LnIII2] [Ln = Ho (1), Dy (2) and Gd (3)] containing mixed organic ligands were obtained. 1 and 2 show slow magnetic relaxation behaviour.

Syntheses, crystal structures and magnetic properties of a series of luminescent lanthanide complexes containing neutral tetradentate phenanthroline-amide ligands

Six lanthanide compounds have been prepared from a neutral tetra-dentate ligand. Their luminescent and magnetic properties were investigated in detail.

Designing a mononuclear DyIII single-molecule magnet (SMM) by using a N,O,N,O-based multichelating Schiff base ligand and a β-diketonate ligand

Two mononuclear Ln^III compounds, in which each Ln^III is eight-coordinated, namely [Ln(L)(tmpd)] (Ln = Dy (1) or Er (2)), have been prepared using a multichelating Schiff base ligand (H₂L) and a bidentate chelating β-diketonate ligand (tmpd).

Tetranuclear lanthanide complexes showing magnetic refrigeration and single molecule magnet behavior

Four tetranuclear lanthanide complexes were fabricated and characterized. 1 exhibits cryogenic magnetic refrigeration property and 3 displays slow relaxation of the magnetization.

Linear-shaped LnIII4 and LnIII6 clusters constructed by a polydentate Schiff base ligand and a β-diketone co-ligand: structures, fluorescence properties, magnetic refrigeration and single-molecule magnet behavior

A series of linear-shaped LnIII4 and LnIII6 clusters were synthesized. The structures, fluorescence properties and magnetic properties have been deeply studied.

A supramolecular chain of dimeric Dy single molecule magnets decorated with azobenzene ligands

Dy^III dimers decorated with photo-isomerizable azobenzene ligands behave as single-molecule magnets and self-organize into a supramolecular chain. Ab initio calculations, magnetic and optical properties are reported.

A series of CuII–LnIII complexes of an N2O3 donor asymmetric ligand and a possible CuII–TbIII SMM candidate in no bias field

Among four isostructural heterometallic Cu^II–Ln^III complexes (Ln = Tb, Dy, Ho or Er) of an N₂O₃ donor asymmetric ligand, only the Cu^II–Tb^III complex shows SMM behavior at zero bias field but at applied bias field both the Cu^II–Tb^III and Cu^II–Dy^III complexes show SMM behavior.

Exploration of SMM behavior of Ln2 complexes derived from thianaphthene-2-carboxylic acid

Observations were made of field-induced SMM property of a dysprosium-based dinuclear complex derived from thianaphthene-2-carboxylic acid ligand.

3D LnIII-MOFs: displaying slow magnetic relaxation and highly sensitive luminescence sensing of alkylamines

Six isomorphous Ln-based MOFs with 3D structures have been synthesized under solvothermal conditions. Dy-MOF (5) shows slow magnetic relaxation behaviors. Eu-MOF (3) can serve as a recyclable sensor towards alkylamines in water systems.