Slow magnetic relaxation in two new 1D/0D Dy(III) complexes with a sterically hindered carboxylate ligand

Russian Doll-like 3d-4f Cluster Wheels with Slow Relaxation of Magnetization

The solvothermal reactions of LnCl3·6H2O and MCl2·6H2O (M = Co, Ni) with 2,2'-diphenol (H2L1) and 5,7-dichloro-8-hydroxyquinoline (HL2) gave three 3d-4f heterometallic wheel-like nano-clusters [Ln7M6(L1)6(L2)6(µ3-OH)6(OCH3)6Cl(CH3CN)6]Cl2·xH2O (Ln = Dy, M = Co, x = 3 for 1; Ln = Dy, M = Ni, x = 0 for 2; Ln = Tb, M = Ni, x = 0 for 3) with similar cluster structure. The innermost Ln(III) ion is encapsulated in a planar Ln6 ring which is further embedded in a chair-conformation M6 ring, constructing a Russian doll-like 3d-4f cluster wheel Ln(III)⸦Ln6⸦M6. 2 and 3 show obvious slow magnetic relaxation behavior with negligible opening of the magnetic hysteresis loop. Such a Russian doll-like 3d-4f cluster wheel with the lanthanide disc isolated by transition metallo-ring is rarely reported.

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.

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.

Single molecule magnet behavior and magnetic refrigeration of carbonyl oxygen-bridged tetranuclear lanthanide complexes

Three lanthanide complexes were fabricated and characterized. 1 exhibited cryogenic magnetic refrigeration property and 3 displayed slow relaxation of the magnetization.

A series of lanthanide(III) metal-organic frameworks derived from a pyridyl-dicarboxylate ligand: single-molecule magnet behaviour and luminescence properties

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to the formation of a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as nine-coordinated muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topological architectures. To the best of our knowledge, the Dy-MOF exhibits zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a diluted sample (1@Y) and ab initio calculations demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence.

2D chain layer versus 1D chain: rigid aromatic benzoate disassembling flexible alicyclic dicarboxylate-based lanthanide coordination polymers with enhanced photoluminescence and characteristic single-molecule magnet behavior

Used as photosensitizer and structural separator, aromatic benzoate activator was grafted on cyclopropane dicarboxylate-based lanthanide coordination polymers with efficient photoluminescence and characteristic behavior of single molecule magnet.

Three 3D LnIII-MOFs based on a nitro-functionalized biphenyltricarboxylate ligand: syntheses, structures, and magnetic properties

Cluster, chain or layer-based 3D Ln-MOFs have been synthesized and they exhibit ferromagnetic or antiferromagnetic interactions. Furthermore, the Dy-MOF shows slow relaxation behavior.

Effective luminescence sensing of Fe3+, Cr2O72-, MnO4- and 4-nitrophenol by lanthanide metal-organic frameworks with a new topology type

Lanthanide MOFs (Ln-MOFs), {[Ln₂(L)₂(H₂O)₂]·5H₂O·6DMAC}_n, [Ln^||| = Eu(1) and Tb(2); H₃L = 4,4'-(((5-carboxy-1,3-phenylene)bis(azanediyl))bis(carbonyl)) dibenzoic acid, DMAC = N,N'-dimethylacetamide], with a new topology type have been isolated. Single crystal X-ray diffraction indicates that complexes 1 and 2 are isostructural with binuclear [Eu₂(COO)₇]_n secondary building units as 7-connected nodes and H₃L ligands as 3-connected nodes and can be viewed as a (5,7)-connected 3D framework with a new topological point symbol of {3²·4⁴·5⁴} {3⁴·4⁶·5⁶·6⁵}. Complexes 1 and 2 exhibit an excellent luminescence sensing response to inorganic ions Fe³⁺, Cr₂O₇^2-, MnO₄^- and 4-nitrophenol, with a low detection limit and high K_sv value. Interestingly, when the MnO₄^- ions are detected, the color of the solid sample is observed to change from yellow to brown, visually indicating luminescence induction, which makes the process of detecting MnO₄^- ions simpler and more practical. Moreover, by using time-resolved photoluminescence techniques, complex 1 can effectively eliminate background fluorescence interference during detection and improve detection accuracy. Solvent luminescence studies, pH stability and PXRD data indicate that complexes 1 and 2 can be used as excellent water-stable multi-response luminescent sensors for detecting a wide variety of toxic substances. In addition, the mechanism of selective detection is explained by the energy competition between the excitation of complexes 1 and 2 and the ultraviolet absorption of the responsive substance.

A Series of Lanthanide-Based Metal-Organic Frameworks Derived from Furan-2,5-dicarboxylate and Glutarate: Structure-Corroborated Density Functional Theory Study, Magnetocaloric Effect, Slow Relaxation of Magnetization, and Luminescent Properties

Herein, through a dual-ligand strategy, we report eight isorecticular lanthanide(III) furan-2,5-dicarboxylic acid metal-organic frameworks (Ln-MOFs) with the general formula {[Ln(2,5-FDA)_0.5(Glu)(H₂O)₂]· xH₂O} _n [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), and Yb (8); 2,5-FDA^2- = furan-2,5-dicarboxylate and Glu^2- = glutarate; x = 0.5 for 1, 2, and 4 and x = 0 for 3 and 5-8], synthesized under solvothermal conditions by using an N, N'-dimethylformamide/H₂O mixed solvent system. Crystallographic data reveal that all eight Ln-MOFs 1-8 crystallize in the orthorhombic Pnma space group. All of the MOFs are isostructural as well as isomorphous with distorted monocapped square-antiprismatic geometry around the Ln1 metal center. In Ln-MOFs 1-8, the 2,5-FDA^2- and Glu^2- ligands exhibit μ₂-κ⁴,η¹:η¹:η¹:η¹ and μ₃-κ⁵,η²:η¹:η¹:η¹ coordination modes, respectively. Topologically, assembled Ln-MOFs 1-8 consist of the 2D cem topological type. The designed Ln-MOFs 1-8 are further explored for structure-corroborated density functional theory study. Meanwhile, room temperature photoluminescence properties of Ln-MOFs 2 and 4 and magnetic properties of Ln-MOFs 3 and 5 have been explored in detail. A highly intense, ligand-sensitized, Ln³⁺ f-f photoluminescence emission is exhibited by Ln-MOFs 2 [Eu³⁺ (red emission)] and 4 [Tb³⁺ (green emission)]. Magnetic studies suggest weak antiferro- and ferromagnetic interactions between adjacent Gd^III ions in Ln-MOF 3, thereby displaying a large magnetocaloric effect. The magnetic data measured at T = 2 K and Δ H = 30 kOe depict that the -Δ S_m value per unit mass reaches 32.1 J kg^-1 K^-1, which is larger than most of the Gd^III-based complexes reported. The alternating-current susceptibility measurements on Ln-MOF 5 revealed that out-of-phase signals are frequency- and temperature-dependent under both 0 and 2 kOe direct-current fields, thereby suggesting a typical slow magnetic relaxation behavior with two relaxation processes. This is further supported by the Cole-Cole plots at 2.4-6 K.

Dy(iii) zig-zag chains assembled in a 3D framework with single-molecule magnet behaviour

A new lanthanide-based framework, [Dy(STP)(1,2-bdc)]_n (1), represents 1D dysprosium zigzag chain architecture in a 3D framework and displays SMM behaviour under zero dc field.

TbIII/3d–TbIII clusters derived from a 1,4,7-triazacyclononane-based hexadentate ligand with field-induced slow magnetic relaxation and oxygen-sensitive luminescence

A family of new Tb^III/3d–Tb^III cluster complexes based on N,N′,N′′-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane have been synthesized and they exhibit interesting magnetic and luminescent properties.

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.

Magnetic, luminescence, topological and theoretical studies of structurally diverse supramolecular lanthanide coordination polymers with flexible glutaric acid as a linker

This contribution explores the topological, supramolecular, magnetic and luminescent properties of previously unknown CPs, which fall into category of glutarates without auxiliary coligands.

High-nuclear heterometallic oxime clusters assembled from triangular subunits: solvothermal syntheses, crystal structures and magnetic properties

Three series of 3d–4f oxime clusters with slightly low magnetic relaxation or large entropy change were solvothermally constructed through the flexible connectivity of triangular {Ln₃(μ₃-OH)} subunits.

A belt-like one-dimensional Dy chain exhibiting slow magnetic relaxation behavior

A belt-like Dy chain compound was synthesized, which exhibited slow magnetic relaxation behavior and clear hysteresis loops below 0.6 K.

Four tetra-nuclear lanthanide complexes based on 8-hydroxyquinolin derivatives: magnetic refrigeration and single-molecule magnet behaviour

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

Lanthanide oxalatophosphonates with two types of layered structures: syntheses, structures, luminescence and magnetic properties

Five novel lanthanide(iii) oxalatophosphonates with two types of 2D layered structures have been hydrothermally obtained and structurally characterized. The luminescence and magnetic properties of the title compounds have been studied.

Magnetic properties and structure of tetranuclear lanthanide complexes based on 8-hydroxylquinoline Schiff base derivative and β-diketone coligand

Herein, we report the synthesis, structure, and magnetism of five tetranuclear Ln^III complexes encapsulated by 5-(4-pyridinecarboxaldehyde)amino-8-hydroxylquinoline and β-diketonate coligand.

Single molecule magnetic behaviour in lanthanide naphthalenesulfonate complexes

A family of mononuclear lanthanide complexes exhibiting slow magnetic relaxation is reported, providing the first examples of pure 4f sulfonate-based single molecule magnets.

Evolution from linear tetranuclear clusters into one-dimensional chains of Dy(iii) single-molecule magnets with an enhanced energy barrier

Structural evolution from Dy₄ clusters into 1D Dy(iii)-chains, the anisotropy energy barrier is enhanced from 45.4(2) to 144.2(1) K.

Three sandwich-type zinc(ii)–lanthanide(iii) clusters: structures, luminescence and magnetic properties

We present herein three sandwich-type luminescent Zn^II–Ln^III clusters with Zn^II–Dy^III being SMMs with a slow zero-field relaxation.

A series of anionic host coordination polymers based on azoxybenzene carboxylate: structures, luminescence and magnetic properties

Series of luminescent or magnetic coordination polymers based on azoxybenzene tetracarboxylic acid and bipyridine have been afforded, and characterized systematically.

Construction of lanthanide single-molecule magnets with the “magnetic motif” [Dy(MQ)4]−

[Dy₂(MQ)₄(NO₃)₃]⁺ is SMM-silent (SMM = single-molecule magnet) owing to the unfavourable magnetic interactions. Introducing an additional “magnetic motif” [Dy(MQ)₄]⁻ to diminish such interactions gave a trinuclear [Dy₃(MQ)₈(NO₃)], which behaves as an SMM.

Dinuclear Ln(iii) complexes constructed from an 8-hydroxyquinoline Schiff base derivative with different terminal groups show differing slow magnetic relaxation

Two series of Ln₂ complexes display substituent-dependent magnetic relaxation behavior.

A Dy4 single-molecule magnet and its Gd(iii), Tb(iii), Ho(iii), and Er(iii) analogues encapsulated by an 8-hydroxyquinoline Schiff base derivative and β-diketonate coligand

We report five tetranuclear Ln^IIIcomplexes encapsulated by 5-(benzylidene)amino-8-hydroxyquinoline and the β-diketonate coligand.

A family of one-dimensional lanthanide complexes bridged by two distinct carboxylate ligands with the Dy analogue displaying magnetic relaxation behaviour

Utilizing two different carboxylate ligands to construct dysprosium SMMs with relatively good performance was proven to be a successful synthetic strategy.

Thermostability and photoluminescence of Dy(iii) single-molecule magnets under a magnetic field

A series of compounds [ADyL₄]·[solvent] composed of a dysprosium(iii) ion coordinated by four chelated naphthyridine-like ligands (L = 4-hydroxy-8-methyl-1,5-naphthyridine-3-carbonitrile) and an alkali metal ion (A = Na, K, Rb, Cs) were synthesized and characterized. They behave as single-molecule magnets under a zero dc field with an effective energy barrier of around 95 cm^-1. Meanwhile, the main part, [ADyL₄], of these SMMs is thermostable and sublimable. The geometric structures of three sublimed compounds are identical to the original ones without solvents, which is confirmed by X-ray diffraction using single crystal and powder samples. The static and dynamic magnetic properties remain unchanged before and after sublimation. Luminescence measurements at 5-77 K were performed to verify the energy gap between low-lying states and to understand the pathway of the thermal relaxation process of magnetization, as well as to inspect the tiny variation in magnetic sublevels for the ground term of Dy(iii). The photoluminescence spectra under a magnetic field (0-36 T) for the Dy-SMMs are investigated for the first time. The energy splitting of the two lowest sublevels of the ground term ⁶H_15/2 of Dy(iii) are analyzed using the Zeeman formula.