Cl--templated coordination polymers constructed from dragonfly-like Ln4 clusters exhibiting excellent magnetothermal properties

Lanthanide clusters with high magnetic entropy and an exquisite structure have always been a hot research direction. Herein, two delicately structured lanthanide clusters were synthesized using isonicotinic acid (HIN) as a ligand by the solvothermal method, namely {[Gd4(IN)4(μ3-OH)4(OAc)2(H2O)6]·Cl2·7H2O}n (1) and {[Dy4(IN)4(μ3-OH)4(OAc)2(H2O)6]·Cl2·8H2O}n (2). Structural analysis indicates that the two compounds exhibit comparable structures, and both have the same cubane-like Ln4 metal skeleton and form an interesting dragonfly molecular configuration by connecting to HIN. Moreover, {Ln4} serves as the fundamental structural unit for the construction of a 1D channel of 1, with a diameter of approximately 10.08 Å, which is connected to each other by extra {Ln4} units to form an exquisite porous 3D structure of 1. Cl- exists as an anion-template in its 3D structure, balancing the charge and maintaining its structural stability. Magnetic measurements indicate that 1 exhibits a rather satisfactory magnetic entropy change, reaching a maximum value of -ΔSmaxm = 31.59 J kg-1 K-1 at 2 K for ΔH = 7 T.

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.

{GdIII7} and {GdIII14} Cluster Formation Based on a Rhodamine 6G Ligand with a Magnetocaloric Effect

Heptanuclear {GdIII7} (complex 1) and tetradecanuclear {GdIII14} (complex 2) were synthesized using the rhodamine 6G ligand HL (rhodamine 6G salicylaldehyde hydrazone) and characterized. Complex 1 has a rare disc-shaped structure, where the central Gd ion is connected to the six peripheral GdIII ions via CH3O-/μ3-OH- bridges. Complex 2 has an unexpected three-layer double sandwich structure with a rare μ6-O2- ion in the center of the cluster. Magnetic studies revealed that complex 1 exhibits a magnetic entropy change of 17.4 J kg-1 K-1 at 3 K and 5 T. On the other hand, complex 2 shows a higher magnetic entropy change of 22.3 J kg-1 K-1 at 2 K and 5 T.

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.

Quick and robust PDF data acquisition using a laboratory single-crystal X-ray diffractometer for study of polynuclear lanthanide complexes in solid form and in solution

Self-assembled polynuclear lanthanide hydroxo complexes are important objects in the reticular chemistry approach to the design of various functional materials. Revealing their structure in the solid state and understanding the molecular mechanism of self-assembly in solution require a universal and reliable structural method. Pair distribution function (PDF) analysis is a powerful technique which enables structural insight for a wide range of crystalline and amorphous materials on the nanoscale, but commonly measurements are performed at synchrotron X-ray sources or on specially designed laboratory diffractometers. In the present paper, a standard Bruker D8 QUEST single-crystal X-ray diffractometer equipped with a micro-focus Mo tube and CMOS Photon III detector was adapted to measure PDF data of high quality with Q max = 16.97 Å–1 for solid and liquid samples. An improved data collection strategy and the original data reduction software FormagiX enable calibration and azimuthal full-frame integration of 2D frames, delivering reliable PDFs up to 80 Å with instrumental parameters Q damp = 0.018 Å−1 and Q broad = 0.010 Å−1. The effectiveness of the developed approach was demonstrated with reference samples and real-case studies of tetranuclear lanthanide hydroxocarboxylates in solid form and in solution.

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.

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...

Magnetocaloric effect and slow magnetic relaxation in peroxide-assisted tetranuclear lanthanide assemblies

Investigation of a series of rare peroxide-assisted tetranuclear lanthanide assemblies revealed both significant magnetocaloric effect and slow magnetic relaxation.

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 Family of Lanthanide Hydroxo Carboxylates with 1D Polymeric Topology and Ln4 Butterfly Core Exhibits Switchable Supramolecular Arrangement

The unique family of coordination polymers [Ln₄(OH)₂(piv)₁₀(H₂O)₂]_∞ of 11 lanthanides (Ln = La-Er) has been prepared by a simple solution method based on controlled hydrolysis. The ribbon-like polymeric structure consisting of connected tetranuclear clusters and supported by pivalate ligands and a framework of H-bonds has been revealed by single-crystal X-ray diffraction. While the compounds demonstrate similar PXRD patterns and unit cell parameters, the joint single-crystal XRD and pair distribution function data suggest the significant local structure change along the lanthanide series. The compounds exist as two packing polymorphs (α and β) with similar ribbon geometry, but different supramolecular arrangement of the ribbons. Dehydration of either polymorph does not disturb the tetranuclear core but leads to a translational symmetry loss along the ribbon and a transformation of the 3D-ordered crystal into a 2D-ordered mesostructure. Rehydration of the mesostructure leads to the β polymorph (except La and Ce), allowing the deliberate switching between the polymorphs via dehydration-rehydration evidenced by means of powder X-ray diffraction, pair distribution function analysis, and density functional theory calculations. Ab initio calculations reveal significant magnetic anisotropy of Ln³⁺ ions with ferro- and antiferromagnetic interactions within tetranuclear [Ln₄(OH)₂(piv)₁₀(H₂O)₂] species. Magnetic susceptibility measurements demonstrated antiferromagnetic coupling, slow magnetic relaxation for Dy, Ho, and Er complexes, and field-induced single-chain magnetism for the Dy compound.

Lanthanide clusters of phenanthroline containing a pyridine-pyrazole based ligand: magnetism and cell imaging

In this contribution, we report the synthesis, characterization and luminescence-magnetic properties of Ln-clusters (Ln = Gd3+, Eu3+ and Tb3+) using a new pyridine-pyrazole functionalized ligand fitted with a chromophoric phenanthroline backbone. The unorthodox N-rich ligand forms isostructural trinuclear lanthanide complexes with a topology that closely resembles two interdigitating hairpins. The clusters crystallize in chiral space groups and also exhibit chirality for bulk samples, which were further confirmed using solid state CD spectra. Magnetic studies on the complexes reveal their interesting features while the Gd cluster shows a significant cryogenic magnetic cooling behaviour with a moderately high magnetic entropy change of -23.42 J kg-1 K-1 at 7 T and 2 K. On the other hand, Eu and Tb complexes exhibit interesting fluorescence properties. The compounds were subsequently used as fluorescent probes for the imaging of human breast adenocarcinoma (MCF7) cells. Live cell confocal microscopy images show that the complexes penetrate beyond the usual cytoplasm region and can be useful in imaging the nucleus region of MCF7 cells.

Magnetic investigation in di- and tetranuclear lanthanide complexes

Dinuclear and tetranuclear dysprosium-based complexes have been constructed by using a crab-like hydrazone ligand, with the former acting as a typical single-molecule magnet and the later showing diamagnetic ground state.

A cobalt complex with 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine: antiferromagnetic couple governed single-molecule-magnet behaviour

One cobalt complex with distorted trigonal antiprismatic geometry was obtained using 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine (dipyatriz) as the ligand. X-ray crystallography showed the complex possessing a pair of metal centers, had an antiferromagnetic coupling between two Co(ii) ions. Further studied showed a field-induced slow relaxation under H_dc = 0.8 kOe. The peak of out-of-phase was observed after 1000 Hz, which exhibited a moderate slow-relaxation behaviour comparing to the magnetic couple for single Co(ii) complex. This study may provide some strategies on designing new functional molecular magnetic materials with distinct magnetic properties and diverse the structures.

One cobalt complex with distorted trigonal antiprismatic geometry was obtained using 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine (dipyatriz) as the ligand.

Symmetrical Noncovalent Interactions Br···Br Observed in Crystal Structure of Exotic Primary Peroxide

4-Bromobenzamidrazone reacts with cyclopentanone giving 3-(4-bromophenyl)-5-(4-peroxobutyl)-1,2,4-triazole, which precipitated as pale-yellow crystals during the reaction. The intermolecular noncovalent interactions Br···Br in the single-crystal XRD structure of the peroxo compound were studied theoretically using quantum chemical calculations (ωB97XD/x2c-TZVPPall) and quantum theory of atoms in molecules (QTAIM) analysis. These attractive intermolecular noncovalent interactions Br···Br is type I halogen···halogen contacts and their estimated energy is 2.2–2.5 kcal/mol. These weak interactions are suggested to be one of the driving forces (albeit surely not the main one) for crystallization of the peroxo compound during the reaction and thus its stabilization in the solid state.

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 hexanuclear lanthanide Ln6III clusters featuring remarkable magnetocaloric effect and slow magnetic relaxation behavior

Two novel hexanuclear lanthanide clusters (1 and 2) were successfully prepared. Magnetic investigations reveal that 1 exhibits remarkable magnetocaloric effect and 2 displays interesting slow magnetic relaxation behaviors.

Construction of a family of Ln3 clusters using multidentate Schiff base and β-diketonate ligands: fluorescence properties, magnetocaloric effect and slow magnetic relaxation

Seven μ-O_{acylhydrazone}-bridged Ln₃ clusters were synthesized. Cluster 3 displayed magnetic refrigeration properties, whereas cluster 5 showed slow magnetic relaxation. The solid-state fluorescence properties of 2, 4 and 5 were also studied.

Structures, magnetic refrigeration and single molecule-magnet behavior of five rhombus-shaped tetranuclear Ln(iii)-based clusters

The rhombus-shaped Gd₄ cluster displays a magnetic refrigeration property, and the Dy₄ cluster shows remarkable SMM behavior.