Tetranuclear Lanthanide Complexes Containing a Hydrazone-type Ligand. Dysprosium [2 × 2] Gridlike Single-Molecule Magnet and Toroic

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Slow magnetic relaxation in a Dy3 triangle and a bistriangular Dy6 cluster

Two lanthanide single-molecule magnets (SMMs) [Dy₃(μ₃-OH)(HL-1)₃(H₂O)₃](NO₃)₂·3H₃O (1, H₃L-1 = (E)-3-(((8-hydroxyquinolin-2-yl)methylene)amino)propane-1,2-diol) and [Dy₆(μ₃-OH)₄(H₂L-2)₄(HL-2)₂(L-2)₂] (2, H₃L-2 = (E)-2-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) were synthesized and characterized structurally and magnetically. Complex 1 contains a triangular Dy₃ core in which the three Dy³⁺ ions share a μ₃-OH^- anion and the deprotonated ligands of (HL-1)^2- serve both capping and bridging functions, while 2 displays a centrosymmetric hexanuclear Dy^III structure with two similar Dy₃ triangular cores ligated by two fully deprotonated (L-2)^3- ligands, each of which shares two μ₃-OH^- anions. All the Dy^III ions are eight-coordinated with quasi D_2d or C_2v symmetry. Magnetic studies reveal that 1 exhibited two-step magnetic relaxation under an applied dc field of 800 Oe, with effective energy barriers of 40.1 and 31.0 K for the slow relaxation (SR) and fast relaxation regimes (FR), respectively. Meanwhile, 2 only showed a tail of slow magnetic relaxation at above 2 K. Ab initio calculations have been carried out to show the nature of their different magnetic properties.

The Role of Magnetic Dipole—Dipole Coupling in Quantum Single-Molecule Toroics

For single-molecule toroics (SMTs) based on noncollinear Ising spins, intramolecular magnetic dipole–dipole coupling favours a head-to-tail vortex arrangement of the semi-classical magnetic moments associated with a toroidal ground state. However, to what extent does this effect survive beyond the semi-classical Ising limit? Here, we theoretically investigate the role of dipolar interactions in stabilising ground-state toroidal moments in quantum Heisenberg rings with and without on-site magnetic anisotropy. For the prototypical triangular SMT with strong on-site magnetic anisotropy, we illustrate that, together with noncollinear exchange, intramolecular magnetic dipole–dipole coupling serves to preserve ground-state toroidicity. In addition, we investigate the effect on quantum tunnelling of the toroidal moment in Kramers and non-Kramers systems. In the weak anisotropy limit, we find that, within some critical ion–ion distances, intramolecular magnetic dipole–dipole interactions, diagonalised over the entire Hilbert space of the quantum system, recover ground-state toroidicity in ferromagnetic and antiferromagnetic odd-membered rings with up to seven sites, and are further stabilised by Dzyaloshinskii–Moriya coupling.

Effect of pyridyl donors from organic ligands versus metalloligands on material design

This review illustrates designs and structures of various coordination frameworks constructed using assorted organic ligands and metalloligands offering pyridyl donors to evaluate the impact of flexibility versus rigidity on material design.

Assembly of chiral 3d–4f wheel-like cluster complexes with achiral ligands: single-molecule magnetic behavior and magnetocaloric effect

With the help of perchlorate ions, chiral M₃Ln₃ wheel-like cluster complexes were constructed from achiral ligands, and showed single-molecule magnetic behavior and magnetocaloric effect.

Discrete and polymeric ensembles based on dinuclear molybdenum(vi) building blocks with adaptive carbohydrazide ligands: from the design to catalytic epoxidation

Discrete and polymeric ensembles based on dimolybdenum(vi) units with adaptive carbohydrazide ligands are described. The polymeric complexes are efficient catalysts for cyclooctene epoxidation under eco-friendly conditions.

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.

‘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 Ru2Co2 [2 × 2] Grid with Localized Single Molecule Magnet Behavior

Metal complexes with a [n × n] gridlike structure are discussed as attractive building blocks for various materials chemistry applications in molecular nanotechnology and electronics, which often rely on the grids' magnetic and redox properties. Most of the known metallogrids are homometallic, though heterometallic systems that comprise two or more different metals promise higher level functionalities. However, heterometallic [n × n] grids are relatively rare, mostly because of the more challenging synthetic strategies. To that end a new heterometallic [2 × 2] grid complex [L₄Ru₂Co₂](BF₄)₄ (2) based on a known pyrazolate-bridged bis(tridentate) compartmental N-donor ligand [L]^- is presented in this work, along with its doubly oxidized congener [L₄Ru₂Co₂](BF₄)₆ (3). In order to prevent scrambling of the different metal ions, a stepwise synthetic approach was implemented in which an inert Ru^II "corner complex" [(HL)₂Ru](BF₄)₂ (1) was isolated first, followed by addition of the more labile Co^II. This exclusively yields the desired [L₄Ru₂Co₂]⁴⁺ with anti-topology, viz., with the Ru^II and Co^II ions situated at opposite corners of the [2 × 2] grid, as confirmed by single crystal X-ray diffraction. 2 can be sequentially oxidized four times, first at the Co vertices and then at the Ru vertices. ¹H NMR spectroscopy as well as ESI mass spectrometry evidenced integrity of the [L₄Ru₂Co₂]^4+/6+ grids in solution. Structural and magnetic analyses revealed that paramagnetic 2 features LS-Ru^II and HS-Co^II ions (LS = low-spin, HS = high-spin) whereas LS-Ru^II and LS-Co^III ions are present in diamagnetic 3. The LS-Ru^II ions in 2 serve to magnetically isolate the HS-Co^II whose coordination geometry is strongly distorted from octahedral. A large and negative axial zero-field splitting value (D = -64 cm^-1) for the local S = 3/2 ions is shown to lead to single molecule magnetic (SMM) properties characterized by a barrier to spin inversion of U_eff = 8.8 cm^-1 and a single relaxation process with τ_o = 3.1 × 10^-5 s. Transition metal [2 × 2] grid complexes showing SMM behavior are extremely rare, and this is the first heterometallic 3d/4d grid system featuring such a magnetic signature.

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.

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.

Triethylamine-templated nanocalix Ln12 clusters of diacylhydrazone: crystal structures and magnetic properties

Three {Ln₁₂} (Ln = Gd (1), Tb (2), Dy (3)) nanocalix clusters with a novel ligand of N,N′-bis(o-vanillidene)-1H-imidazole-4,5-dicarbohydrazide (H₅ovih) were synthesized via the amine-templating strategy.

Butterfly-shaped tetranuclear Ln4 clusters showing magnetic refrigeration and single molecule-magnet behavior

A series of butterfly-shaped LnIII4 clusters were successfully synthesized. Magnetic studies show that the Gd₄ cluster displays magnetic refrigeration (ΔS_m = 18.85 J kg⁻¹ K⁻¹ for ΔH = 7.0 T at 2.5 K), while the Dy₄ cluster shows SMMs behavior with ΔE/k_B of 79.15 K and τ₀ of 5.82 × 10⁻⁸ s.

Diacylhydrazone-assembled {Ln11} nanoclusters featuring a “double-boats conformation” topology: synthesis, structures and magnetism

A family of {Ln₁₁} (Ln = Gd, Tb and Dy) nanoclusters were assembled with the diacylhydrazone ligand. They feature an unprecedented “double-boats conformation” topology, which had not been previously reported. {Gd₁₁} and {Dy₁₁} display MCE and SMM behavior, respectively.

Synthesis, structures and magnetism of heterotrimetallic Ni–Cu–Ln complexes based on a dicompartmental imine–oxime ligand

Four Ni^II–Cu^II–Ln^III heterotrimetallic complexes have been prepared and structurally characterized. The Dy derivative behaves as a SMM with a small effective energy of 0.78 K under zero dc-applied field.