A single-ion magnet building block strategy toward Dy2 single-molecule magnets with enhanced magnetic performance

A molecular dysprosium(III) complex [Dy(DClQ)₃(H₂O)₂] (1) was used as a building unit for the construction of lanthanide SMMs, leading to the isolation of two dinuclear Dy(III) complexes, namely [Dy₂(DClQ)₆(MeOH)₂] (2) and [Dy₂(DClQ)₆(bpmo)₂]·6MeCN (3) (DClQ = 5,7-dichloro-8-hydroxyquinoline, bpmo = 4,4'-dipyridine-oxide). Structural analyses revealed the same N₃O₅ coordination environment of the Dy(III) centers with a distorted biaugmented trigonal prism (C_2V symmetry) and triangular dodecahedron (D_2d symmetry) for 2 and 3, respectively. Magnetic studies revealed the presence of ferromagnetic and weak antiferromagnetic exchange interactions between the Dy³⁺ centers in 2 and 3, respectively. Interestingly, slow relaxation of magnetization at zero fields was evidenced with an U_eff of 51.4 K and 159.0 K for complexes 2 and 3, respectively. The detailed analysis of relaxation dynamics discloses that the Orbach process is dominant for 2 whereas Raman and QTM play an important role in 3. Theoretical calculations were carried out to provide insight into the magnetic exchange interactions and relaxation dynamics for the complexes. Due to a single-ion magnet (SIM) of 1, the foregoing results demonstrate a SIM modular synthetic route for the preparation of dinuclear lanthanide SMMs.

Construction of a High Nuclear Gadolinium Cluster with Enhanced Magnetocaloric Effect through Structural Transition

Starting from a dinuclear complex {Gd₂(L)₂(NO₃)₄(H₂O)₂}·2(CH₃CN) (1) based on 2,6-dimethoxyphenol (HL), a nonanuclear cluster {Gd₉(L)₄(μ₄-OH)₂(μ₃-OH)₈(μ₂-OCH₃)₄(NO₃)₈ (H₂O)₈}(OH)·2H₂O (2) was obtained via modulating the amount of the ligand and base. Both of them have been structurally and magnetically characterized. Complex 1 decorates the Gd₂ core bridged by double μ₂-phenoxyl oxygen atoms and coordinated neutral CH₃CN molecules, while 2 features the Gd₉ core with a sandglass-like topology. Magnetic investigations reveal that the weaker antiferromagnetic interactions between adjacent metal ions exist in complex 2 than in 1, which is in agreement with the theoretical results. Meanwhile, the magnetocaloric effect with a maximum -ΔS _m value changes from 27.32 to 40.60 J kg^-1 K^-1 at 2 K and 7 T.

Modulating the relaxation dynamics via structural transition from a dinuclear dysprosium cluster to a nonanuclear cluster

A dinuclear dysprosium cluster [Dy₂(NO₃)₄(H₂O)₂(L)₂]·2CH₃CN was successfully prepared by employing HL (HL = 2,6-dimethoxyphenol) and Dy(NO₃)₃·6H₂O in a mixture of CH₃OH and CH₃CN. The conversion of this Dy₂ compound by reaction with additional deprotonated ligand generated a Dy₉ cluster [Dy₉(μ₄-OH)₂(μ₃-OH)₈(μ₂-OCH₃)₄(NO₃)₈(H₂O)₈(L)₄](OH)·2H₂O with the well-known "diabolo" topology. Magnetic investigation revealed that both of the clusters exhibit typical SMM characteristics, and variable magnetic relaxation with the energy barrier changing from 217.87 K to 9.24 K along with the transition from a dinuclear dysprosium cluster to a nonanuclear one. Ab initio calculations further confirm the corresponding structure-activity relationships that originate the different magnetic behaviours. This design may afford a feasible strategy for modulating the magnetic relaxation dynamics of polynuclear systems.

Azide-Coordination in Homometallic Dinuclear Lanthanide(III) Complexes Containing Nonequivalent Lanthanide Metal Ions: Zero-Field SMM Behavior in the Dysprosium Analogue

A series of homometallic dinuclear lanthanide complexes containing nonequivalent lanthanide metal centers [Ln₂(LH₂)(LH)(CH₃OH)(N₃)]·xMeOH·yH₂O [1, Ln = Dy^III, x = 0, y = 2; 2, Ln = Tb^III, x = 1, y = 1] have been synthesized [LH₄ = 6-((bis(2-hydroxyethyl)amino)-N'-(2-hydroxybenzylidene)picolinohydrazide] and characterized. The dinuclear assembly contains two different types of nine-coordinated lanthanide centers, because the nonequivalent binding of the azide co-ligand as well as the varying coordination of the deprotonated Schiff base ligand. Detailed magnetic studies have been performed on the complexes 1 and 2. Complex 1 and its diluted analogue (1_5%) are zero-field SMMs with effective energy barriers (U_eff) of magnetization reversal equal to 59(3) K and 66(3) K and relaxation times of τ₀ = 10(4) × 10^-6 s and 10(4) × 10^-8 s, respectively. On the other hand, complex 2 shows a field-induced SMM behavior. Combined ab initio and density functional theory calculations were performed to explain the experimental findings and to unravel the nature of the magnetic anisotropy, exchange-coupled spectra, and magnetic exchange interactions between the two lanthanide centers.

Seven-coordinate LnIII complexes assembled from a bulky MesacacH ligand: their synthesis, structure, photoluminescence and SMM behaviour

The reaction of a bulky acetyl acetone ligand 1,3-dimesitylpropane-1,3-dione (MesacacH) with hydrated lanthanide chlorides in the presence of tetramethylammonium hydroxide afforded a new family of neutral mononuclear LnIII complexes [Ln(Mesacac)3(DMF)] (Ln = Dy (1); Tb (2); Y0.91Dy0.09 (3); and Er (4)). The molecular structures of these complexes were confirmed by single crystal X-ray diffraction studies. The coordination geometries of the LnIII centre were analysed by SHAPE analysis which revealed a capped octahedral geometry in 1-4. Photoluminescence studies showed ligand-sensitized green emissions for 2 with an appreciable quantum yield of 0.83%. Static (dc) and dynamic (ac) magnetic studies of complexes 1 and 3 were performed. The dynamic magnetic study revealed that complex 1 exhibits zero-field slow relaxation of the magnetization without showing a clear maximum in the out-of-phase ac susceptibility plots. However, magnetic dilution of 1 with the YIII metal ion (complex 3) and/or the application of a dc magnetic field induces a strong frequency dependence of the ac susceptibility signals with χ''M peaks in the 3-10 K temperature range, thus supporting field-induced SMM behaviour of 1. The relaxation process takes place through a combination of the Orbach and Raman mechanisms. The fitting of the temperature dependence of the relaxation time to the equation τ-1 = τ0-1 exp(-Ueff/kBT) + BTn, allows the extraction of the effective energy barrier Ueff/kB = 70 K (48.7 cm-1) and pre-exponential parameter of τ0 = 2.7 × 10-7 s for the Orbach mechanism (first term) and the parameters B = 0.04 s-1 K-n and n = 6.11, for the Raman mechanism (second term).

Arraying Octahedral {Cr2Dy4} Units into 3D Single-Molecule-Magnet-Like Inorganic Compounds with Sulfate Bridges

Two novel 3D pure inorganic compounds based on [Cr₂Dy₄(μ₄-O)₂(μ₃-OH)₄]¹⁰⁺ cluster units and sulfate anions are presented. Both complexes exhibit single-molecule-magnet (SMM)-like behavior. Permutation of the magnetic moment direction among SMM-like cluster units has a significant effect on the performance of molecular nanomagnets, and directional consistency shows obvious advantages.

A series of Ln2 complexes based on an 8-hydroxyquinoline derivative: slow magnetization relaxation and photo-luminescence properties

A series of Ln₂ complexes display slow magnetization relaxation and photo-luminescence properties.

Eight homodinuclear lanthanide complexes prepared from a quinoline based ligand: structural diversity and single-molecule magnetism behaviour

Eight dinuclear complexes are prepared and characterized; complex 6 exhibits SMM behavior with a U_eff value of 14.83 K.

Modulating the magnetization dynamics of four phenoxo-O bridged Dy2 complexes based on a Schiff base derived from 8-hydroxyquinoline

The quantum tunneling process in Dy-SMMs is suppressed by the application of a dc field.

A wheel-shaped Dy(iii) single-molecule magnet supported by polyoxotungstates

A wheel-shaped Dy(iii) single-molecule magnet with an idealized S₆ symmetry is supported by polyoxotungstates. The anisotropic barrier is extracted from AC susceptibilities and the emission spectrum offers insight into the magneto-optical correlation.