Hourglass-Shaped Homo- and Heteronuclear Nonanuclear Lanthanide Clusters: Structures, Magnetism, Photoluminescence, and Theoretical Analysis

Synthesis of nonameric cationic clusters [Dy9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (1), [Dy8Tb (acac)16(μ3-OH)8(μ4-OH)2]OH·2H2O (2), and [Gd9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the 4F9/2 → 6HJ (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the 5D4 → 7FJ (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -ΔSm values increasing with decrease in temperature and increase in field, reaching -ΔSmmax = 20.98 J kg-1 K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (Js) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)···Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

Bifunctional Lanthanide-Based Coordination Polymers: Conversion of CO2 and Highly Selective Luminescence Sensing for Acetylacetone

A series of bifunctional Ln(III)-based coordination polymers (CPs) {Ln(L)(DMA)2(NO3)}n [Ln(III) = Eu (1), Gd (2), and Dy (3); organic ligand H2L = 2,2'-(1,3,5,7-tetrahydroxyoctahydro-4,8-ethanopyrrolo[3,4-f]isoindole-2,6(1H,3H)-diyl)diacetic acid)] have been successfully synthesized. CPs 1-3 are isostructural and constructed from the dimeric Ln2 unit in which two adjacent LnIII ions are bridged by two μ3-carboxyl oxygens, and the Ln2 dimeric unit is connected by two NO3- ions, four DMA molecules, and four completely protonated L2- ligands forming a 2D layer structure. The magnetic research reveals that CP 2 shows a significant cryogenic magnetocaloric effect (-ΔSm = 22.9 J kg-1 K-1; T = 2.0 K and ΔH = 7.0 T), whereas CP 3 exhibits slow magnetic relaxation property under Hdc = 0 Oe field. Additionally, the luminescence explorations revealed that CP 1 can act as a recyclable luminescent probe for pollutant acetylacetone among various small organic solvent molecules, and the corresponding detection limit is 10-7 mol/L. More importantly, CP 1 also exhibits good catalytic performance in the cycloaddition reaction of CO2 and epoxides or cyanamides under mild conditions. As far as we know, CP 1 represents the first bifunctional lanthanide homogeneous catalyst that can efficiently catalyze the reaction of cyanamides/epoxides with CO2 simultaneously.

Self-assembly of octanuclear Ln(III)-based clusters: their large magnetocaloric effects and highly efficient conversion of CO2

The design and construction of high-nuclear lanthanide clusters with fascinating topology and functional properties have been an active area of research, however, the development of an effective approach for obtaining high-nuclear lanthanide clusters with multifunctional properties is still extremely difficult. Up to now, a systematic approach for guiding the further expansion of Ln(III)-based clusters showing good functional properties is lacking. Herein, we design and synthesize a polydentate Schiff base ligand (HL), which reacts with β-diketonate salts Ln(acac)₃·2H₂O, and a series of Ln₈ clusters [Ln₈(acac)₆(L)₂(μ₃-O)₆(μ₂-C₂H₅O)₄(μ₂-Hacac)₂]·2CH₃CN (Ln(III) = Gd (1), Dy (2), and Ho (3); HL = pyridine-2-carboxylic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide, Hacac = acetylacetone) have been successfully synthesized. Single-crystal X-ray diffraction studies reveal that clusters 1-3 are isostructural and can be viewed as a Ln₈ core bridged by eighteen μ₂-O atoms, six μ₃-O atoms and two μ₄-O atoms. Magnetic studies show that cluster 1-Gd8 displays a large magnetocaloric effect with -ΔS_m = 46.14 J kg^-1 K^-1 (T = 2.0 K and ΔH = 7.0 T); cluster 2-Dy8 exhibits single-molecule magnet behavior under zero-field conditions. It is worth mentioning that the -ΔS_m of cluster 1-Gd8 is larger than that of most reported polynuclear Gd(III)-based clusters; the 2-Dy8 cluster is one of the rare polynuclear Ln_n SMMs (n ≥ 8) under zero dc field. Importantly, these Ln(III)-based clusters (1-3) can catalyze the cycloaddition of CO₂ with epoxides with high efficiency under mild conditions; and cluster 1-Gd8 as a catalyst could be reused at least three times without obvious loss of catalytic performance.

Magnetic cooling: a molecular perspective

The magnetocaloriceffect is considered as an energy-efficient and environmentally friendly technique which can take cooling technology to the next level. Apart from its commercial application at room temperature, magnetic refrigeration is an up-and-coming solution for the cryogenic regime, especially as an alternative to He³ systems. Molecular magnets reveal advantageous features for ultra-low cooling which are competitive with intermetallic and lanthanide alloys. Here, we present a guide to the current status of magnetocaloric effect research of molecular magnets with a theoretical background focused on the inverse magnetocaloric effect and an overview of recent results and developments, including the rotating magnetocaloric effect.

3-Pyridylacetic-Based Lanthanide Complexes Exhibiting Magnetic Entropy Changes, Single-Molecule Magnet, and Fluorescence

Four complexes from lanthanides, 3-pyridylacetate, and 1,10-phenanthroline, formulated as [Ln2(3-PAA)2(μ-Cl)2(phen)4](ClO4)2 [Ln = Gd(1), Dy(2), Eu(3), Tb(4), 3-PAA = 3-pyridylacetic acid, phen = 1,10-phenanthroline], were obtained. The four compounds were characterized by IR spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1-4 are isomorphous, and they have a dinuclear structure. Magnetic studies reveal that 1 shows the magnetocaloric effect with -ΔS m max = 19.03 J kg-1 K-1 at 2 K for ΔH = 5 T, and 2 displays a field-induced single-molecule magnet with U eff = 19.02 K. The photoluminescent spectra of 3 and 4 exhibit strong characteristic emission, which demonstrate that the ligand-to-EuIII/TbIII energy transfer is efficient.

Conversion of a double-tetranuclear cluster silver helicate into a dihelicate via a rare desulfurization process

We show the first example of a bisthiosemicarbazone silver double-tetranuclear cluster helicate [Ag4L2]2 obtained by electrochemical synthesis which undergoes a rare desulfurization process giving rise to a cationic silver dihelicate [Ag2(H2L)2]SO4.

A new family of boat-shaped Ln8 clusters exhibiting the magnetocaloric effect and slow magnetic relaxation

Designing and synthesizing lanthanide clusters have always been a research hotspot. Herein, three lanthanide clusters with the formula [Ln₈(IN)₁₄(μ₃-OH)₈(μ₂-OH)₂(H₂O)₈]·xH₂O (Ln = 1-Gd and x = 11; Ln = 2-Dy and x = 8; Ln = 3-Eu and x = 8) have been isolated in the presence of isonicotinic acid under solvothermal conditions. Structural analysis indicates that those three compounds are isostructural, featuring boat-shaped {Ln₈} metal frameworks. Magnetic measurements reveal that 1-Gd exhibits a larger MCE with the maximum -ΔS_m value of 31.77 J kg^-1 K^-1 at 2 K for ΔH = 7 T, while 2-Dy displays slow magnetization relaxation. Besides, the photoluminescence properties of 3-Eu were investigated.

Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different β-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours

A series of tetranuclear lanthanide-based clusters [Ln₄(dbm)₆(L)₂(CH₃OH)₄]·2CH₃OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H₃L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln₈(HL)₁₀(CH₃O)₄(CH₃OH)₂]·6CH₃OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H₃L and two different β-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, β-diketones play an important role in assembling and affecting the structures of Ln₄ to Ln₈ clusters. This is the first use of β-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln₄ clusters to Ln₈ clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd4 and 4-Gd8. More importantly, clusters 1-Gd4 and 4-Gd8 display significant cryogenic magnetic refrigeration properties (-ΔS_m = 24.88 J kg^-1 K^-1 for 1-Gd4 and -ΔS_m = 32.52 J kg^-1 K^-1 for 4-Gd8); the results show that cluster 4-Gd8 exhibits a larger magnetocaloric effect than 1-Gd4. Cluster 2-Dy4 shows remarkable single-molecule magnet (SMM) behavior (ΔE/k_B = 67.5 K and τ₀ = 3.06 × 10^-7 s) under a zero dc field, and 5-Dy8 exhibits a field-induced SMM-like behavior (ΔE/k_B = 39.83 K and τ₀ = 2.12 × 10^-7 s) under a 5000 Oe dc field.

A new family of dinuclear lanthanide complexes exhibiting luminescence, magnetic entropy changes and single molecule magnet behaviors

Four isomorphic and dinuclear lanthanide complexes were synthesized. Complexes Eu^III and Tb^III exhibit strong emissions, while Gd^III shows the magnetocaloric effect and Dy^III displays a single-molecule magnet.

Structures and magnetic properties of novel Ln(iii)-based pentanuclear clusters: magnetic refrigeration and single-molecule magnet behavior

The Gd5 cluster displays significant magnetic refrigeration properties, whereas the Dy5 cluster exhibits remarkable SMM behavior. Clusters 2, 4, and 5 display the characteristic lanthanum luminescence.

Two GdIII complexes with different structures and magnetocaloric properties induced by metal ion sources

Two 0D/3D Gd^III complexes based on dl-malic acid have been constructed and they display weak ferromagnetic behaviors and significant MCEs.