Metallogrid Single-Molecule Magnet: Solvent-Induced Nuclearity Transformation and Magnetic Hysteresis at 16 K

Self-Assembled Lanthanide Phosphinate Square Grids (Ln = Er, Dy, and Tb): Dy4 Shows SMM/SMT and Tb4 SMT Behavior

Tetranuclear [2 × 2] square-grid-like LnIII clusters have been synthesized by reacting LnCl3·6H2O salts with bis[α-hydroxy(p-bromophenyl)methyl]phosphinic acid [R2PO2H, where R = CH(OH)PhBr] and pivalic acid. Single-crystal X-ray diffraction studies show the formation of [Me4N]2[Ln4(μ2-η1:η1-PO2R2)8(η2-CO2But)4(μ4-CO3)] [Ln = Er (1), Dy (2), and Tb (3)]. Direct-current studies reveal significant ferromagnetic interactions between DyIII in 2 and TbIII in 3 and an antiferromagnetic interaction between ErIII in 1. Dynamic magnetic susceptibility measurements confirm a single-molecule magnet (SMM) behavior in both 0 and 1200 Oe applied magnetic fields for 2. Complexes 2 and 3 show single molecular toroic (SMT) behavior with a mixed magnetic moment.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

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.

Data-driven design of molecular nanomagnets

Three decades of research in molecular nanomagnets have raised their magnetic memories from liquid helium to liquid nitrogen temperature thanks to a wise choice of the magnetic ion and coordination environment. Still, serendipity and chemical intuition played a main role. In order to establish a powerful framework for statistically driven chemical design, here we collected chemical and physical data for lanthanide-based nanomagnets, catalogued over 1400 published experiments, developed an interactive dashboard (SIMDAVIS) to visualise the dataset, and applied inferential statistical analysis. Our analysis shows that the Arrhenius energy barrier correlates unexpectedly well with the magnetic memory. Furthermore, as both Orbach and Raman processes can be affected by vibronic coupling, chemical design of the coordination scheme may be used to reduce the relaxation rates. Indeed, only bis-phthalocyaninato sandwiches and metallocenes, with rigid ligands, consistently present magnetic memory up to high temperature. Analysing magnetostructural correlations, we offer promising strategies for improvement, in particular for the preparation of pentagonal bipyramids, where even softer complexes are protected against molecular vibrations.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Bis-pyrazolone-based dysprosium(III) complexes: zero-field single-molecule magnet behavior in the [2 × 2] grid DyIII4 cluster

We assembled two new Dy(III) compounds, namely, [Dy4(L1)4(OH)4]·2CH3OH (1) and [Dy2(L2)2(HL2)2(CH3CN)2]N(C2H5)3 (2) (where H2L1 and H2L2 are methyl-substituted and p-tolyl substituted ligands respectively) using a bis-pyrazolone carbohydrazide based multi-dentate hydrazone...

Radical-Bridged Ln4 Metallocene Complexes with Strong Magnetic Coupling and a Large Coercive Field

Inducing magnetic coupling between 4f elements is an ongoing challenge. To overcome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals, which strongly couple with f-block metallocenes to form discrete tetranuclear complexes. Synthesis, structure, and magnetic properties of two tetranuclear [(Cp*₂ Ln)₄ (tz^. )₄ ]⋅3(C₆ H₆ ) (Cp*=pentamethylcyclopentadienyl; tz=1,2,4,5-tetrazine; Ln=Dy, Gd) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements as well as computational studies support a highly sought-after radical-induced "giant-spin" model. Strong exchange interactions between the Ln^III ions and tz^. radicals lead to a strong magnet-like behaviour in this molecular magnet with a large coercive field of 30 kOe.

Influence of the Different Types of Auxiliary Noncarboxylate Organic Ligands on the Topologies and Magnetic Relaxation Behavior of Zn-Dy Heterometallic Single Molecule Magnets

In this work, we first synthesized a Zn-Dy complex, [Zn₆Dy₂(L)₆(tea)₂(CH₃OH)₂]·6CH₃OH·8H₂O (H₂L = N-3-methoxysalicylidene-2-amino-3-hydroxypyridine, teaH₃ = triethanolamine, 1), by employing H₂L, anhydrous ZnCl₂, and Dy(NO₃)₃·5H₂O reacting with auxiliary ligand teaH₃ in the mixture of CH₃OH and DMF. When teaH₃ and the solvent CH₃OH in the reaction system of 1 were replaced by the auxiliary ligand 2,6-pyridinedimethanol (pdmH₂) and the solvent MeCN, another Zn-Dy complex, [Zn₄Dy₄(L)₆(pdm)₂(pdmH)₄]·10CH₃CN·5H₂O (2), was obtained. For 1, its crystal structure can be viewed as a dimer of two Zn₃Dy^III units. However, for 2, four Dy^III form a zigzag arrangement, and each of its terminals linked two Zn^II ions. Interestingly, although the structural topologies of 1 and 2 are different, the coordination geometries of Dy^III in 1 and 2 are all triangular dodecahedron (TDD-8). The difference is that the continuous shape measure (CShM) values of Dy^III in 1 are larger than the corresponding values in 2. Magnetic investigation revealed that the diluted sample 1@Y exhibits two magnetic relaxation processes, while 2 only exhibits a single relaxation process. Ab initio calculations indicated that, in the crystal lattice of 1, two complexes exhibiting slightly different CShM values of Dy^III result in the double relaxation behavior of 1@Y. However, for 2, one of two Dy^III fragments possesses a fast quantum tunneling of magnetization (QTM), resulting in its magnetic process presented at T < 1.8 K, so 2 exhibits single relaxation behavior. More importantly, the theoretical calculations also clearly indicated that the weak ligation at equatorial sites of Dy^III in 1 and 2 ensure 1@Y and 2 possess SMM behavior, although the coordination geometry of Dy^III (TDD-8) in 1 and 2 severely deviates from the ideal polyhedron and its axial symmetry is low.

Magnet Creation by Guest Insertion into a Paramagnetic Charge-Flexible Layered Metal-Organic Framework

Changing nonmagnetic materials to spontaneous magnets is an alchemy-inspiring concept in materials science; however, it is not impossible. Here, we demonstrate chemical modification from a nonmagnet to a bulk magnet of either a ferrimagnet or antiferromagnet, depending on the adsorbed guest molecule, in an electronic-state-flexible layered metal-organic framework, [{Ru₂(2,4-F₂PhCO₂)₄}₂TCNQ(EtO)₂] (1; 2,4-F₂PhCO₂^- = 2,4-difluorobenzoate; TCNQ(EtO)₂ = 2,5-diethoxy-7,7,8,8-tetracyanoquinodimethane). The guest-free paramagnet 1 undergoes a thermally driven intralattice electron transfer involving a structural transition at 380 K. This charge modification can also be implemented by guest accommodations at room temperature; 1 adsorbs several organic molecules, such as benzene (PhH), p-xylene (PX), 1,2-dichloroethane (DCE), dichloromethane (DCM), and carbon disulfide (CS₂), forming 1-solv with intact crystallinity. This induces an intralattice electron transfer to produce a ferrimagnetically ordered magnetic layer. According to the interlayer environment tuned by the corresponding guest molecule, the magnetic phase is consequently altered to a ferrimagnet for the guests PhH, PX, DCE, and DCM or an antiferromagnet for CS₂. This is the first demonstration of the postsynthesis of bulk magnets using guest-molecule accommodations.

Crystal structure of bis-{2-hy-droxy-N'-[1-(pyrazin-2-yl)ethyl-idene]benzohydrazidato}cadmium(II)

In the title complex mol-ecule, [Cd(C13H11N4O2)2], the Cd atom is coordinated in a distorted octa-hedral geometry by two tridentate ligands synthesized from 2-hy-droxy-benzohydrazide and 1-(pyrazin-2-yl)ethan-1-one. The mol-ecule has twofold crystallographic symmetry and is isomorphous to its Mn, Co, Ni, Cu and Zn counterparts.

Solvent-induced structural transformation from heptanuclear to decanuclear [Co–Ln] coordination clusters: trapping of unique counteranion and understanding of aggregation pathways

The MeCN solvent-induced transformations of heptanuclear LnIII3CoII2CoIII2⁺ cationic aggregates, associated with literature unknown Ln(iii)-pivalate-based counter anions, to decanuclear LnIII3CoII3/2CoIII4/5 clusters have been investigated.

Macrocycle supported dimetallic lanthanide complexes with slow magnetic relaxation in Dy2 analogues

Six dimetallic lanthanide complexes, [Ln2(L')(acac)4] (1Dy-3Gd) (Ln = Dy (1Dy), Tb (2Tb) and Gd (3Gd)) and [Ln2(L')(tfac)4] (4Dy-6Gd) (Ln = Dy (4Dy), Tb (5Tb) and Gd (6Gd)) (H2L' = 1,9-dichloro-3,7,11,15-tetraaza-1,9(1,3)-dibenzenacyclohexadecaphane-2,10-diene-1,9-diol), have been synthesized by the reaction of lanthanide nitrates with the HL ligand in the presence of acetylacetonate (acac) (or trifluoroacetylacetonate (tfac) and triethylamine (HL = 4-chloro-2,6-bis(-((3-((3-(dimethylamino)propyl)amino)propyl)imino)methyl)phenol). Ln-Assisted modification of the Schiff base HL occurred and led to the formation of a new macrocyclic ligand (H2L'). X-ray crystallographic analysis revealed that the LnIII ions of complexes 1Dy-6Gd are all eight-coordinated in a square antiprismatic geometry with D4d local symmetry. Magnetic measurements of these complexes revealed that 1Dy and 4Dy show single-molecule magnet behaviour with energy barriers of 66.7 and 79.0 K, respectively, under a zero direct magnetic field. The orientations of the magnetic axes and crystal field parameters were obtained from theoretical calculations and an electrostatic model. The magneto-structural correlations of SMMs 1Dy and 4Dy are further discussed in detail.

The effect of coordinated solvent molecules on metal coordination environments in single-crystal-to-single-crystal transformations

We summarized the effect of coordinated solvent molecules on the metal coordination environments in single-crystal to single-crystal transformations.

Rare CH3O−/CH3CH2O−-bridged nine-coordinated binuclear DyIII single-molecule magnets (SMMs) significantly regulate and enhance the effective energy barriers

This work presents an efficient approach to regulating and enhancing the magnetic anisotropy barriers through using bridged CH₃O⁻ anion or CH₃CH₂O⁻ anion and constructing triple bridges.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.

‘Windmill’-shaped LnIII4 (LnIII = Gd and Dy) clusters: magnetocaloric effect and single-molecule-magnet behavior

Two ‘windmill’-shaped Ln₄ clusters (1 and 2) have been synthesized. The magnetic study reveals that 1 displays a larger cryogenic magnetocaloric effect, while 2 exhibits SMM behavior.

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 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.

Large magnetocaloric effect and remarkable single-molecule-magnet behavior in triangle-assembled LnIII6 clusters

Two intriguing triangle-assembled LnIII6 clusters (1 and 2) have been synthesized. The magnetic study reveals that 1 displays a larger cryogenic magnetocaloric effect, while 2 exhibits remarkable SMM behaviors.

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.

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.

A new family of {Co4Ln8} metallacrowns with a butterfly-shaped structure

A series of cobalt–lanthanide metallacrowns (MCs) {CoIII4Ln₈} (Ln = Dy³⁺1, Ho³⁺2 and Tm³⁺3) based on pyrazinehydroxamic acid (H₂pyzha) and pyrazinic acid (Hpyzic) ligands have been synthesized.

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.

Structures, fluorescence properties and magnetic properties of a series of rhombus-shaped LnIII4 clusters: magnetocaloric effect and single-molecule-magnet behavior

A family LnIII4 clusters were successfully synthesized and structurally characterized. Magnetic studies show that Gd₄ cluster displays magnetic refrigeration, while Dy₄ cluster demonstrates two distinct slow magnetic relaxation processes.