LnIII/MnII-LnIII complexes derived from a salicylic azo dye ligand: synthesis, structures, magnetic and fluorescence properties

Two LnIII complexes Ln(HTMSA)3(H2O)2·5.5H2O (Ln = Dy (1) and Tb (2), H2TMSA = 5-azotriazolyl-3-methoxysalicylaldehyde) and two MnII-LnIII clusters [Mn(H2O)6][MnLn2(TTMSA)4(HTTMSA)2(H2O)6]·4H2O (Ln = Dy (3) and Tb (4), H2TTMSA = 5-azotetrazolyl-3-methoxysalicylaldehyde) have been synthesized and structurally characterized. Single-crystal X-ray diffraction reveals that 1 and 2 are isostructural complexes in which the LnIII ions are surrounded by six oxygen atoms from three chelate HTMSA ligands and two oxygen atoms from two coordinated water molecules forming a distorted square-anti-prismatic geometry. In complexes 3 and 4, the MnII ions adjust two LnIII mononuclear anion clusters into tri-nuclear LnIII-MnII-LnIII anion clusters, with an additional [Mn(H2O)6]2+ as a counter ion to maintain the electroneutrality of the compound. Magnetic studies reveal that all the complexes 1-4 show nonzero out-of-phase signals, indicating single-molecule magnet behavior. The photoluminescence spectra of all the complexes were investigated and are discussed in detail.

Side-Group Effect on the Slow Relaxations of {Dy2} Single-Molecule Magnets with Confined N2O6 Donors

Deep insights into and substantial enhancement of the effective anisotropy energy barrier for magnetization reversal (U_eff) are vitally important for the technological applications of dysprosium(III)-based single-molecule magnets (Dy-SMMs). To fully refine the ligand-field effect on spin relaxation, four centrosymmetric {Dy₂} entities with formula [Dy₂(CH₃OH)₂L₂(RCOO)₂] (H₂L = 2-hydroxy-N'-((pyridin-2-yl)methylene)benzohydrazide) have been solvothermally prepared by varying the side groups of carboxylate coligands (RCOO^-, R = CF₃ for 1, H for 2, CH₃ for 3, and Cp₂Fe for 4). Structural analyses reveal that all of the Dy^III carriers in 1-4 have the same N₂O₆ donor environments, and the non-coordinative R groups attached to the equatorial carboxylate bridges have not substantially changed the binding ability of the shortest Dy-O_phenolate bonds located at the axial position of the ligand field. Interestingly, the side groups have monotonically decreased the zero-field U_eff barriers of these weak antiferromagnetically coupled {Dy₂} analogues from 721 K down to 379 K. Further electronic structure calculations demonstrate that the main magnetic axes of 1-4 are highly dominated by these comparable Dy-O_phenolate short bonds, and the g tensors have produced gradually increased transverse components responsible significantly for the decreased U_eff barriers. Additionally, thermally assisted relaxations occur preferably through the second (for 1) and the first (for 2-4) Kramer doublets. These interesting findings afford a new side-group effect to comprehensively understand the magnetostructural relationships and advance the rational design of high-performance Dy-SMMs.

Zero-field slow magnetic relaxation behavior of Zn2Dy in a family of trinuclear near-linear Zn2Ln complexes: synthesis, experimental and theoretical investigations

We hereby report a series of near-linear trinuclear [Zn₂Ln^III(HL)₄(CH₃COO)]·(NO₃)₂ (where Ln^III = La (1-La), Ce (2-Ce), Nd (3-Nd), Sm (4-Sm), Tb (5-Tb), and Dy (6-Dy)) complexes with Schiff base ligand (H2L). Magnetization relaxation dynamic studies on complexes 2-Ce, 5-Tb, and 6-Dy reveal the existence of well resolved frequency dependent zero-field out-of-phase χ''_M signals, which is an indicator of a typical single-ion magnet behavior observed only for complex 6-Dy with U_eff = 43.7 K (τ₀ = 2.42 × 10^-6 s). The presence of two Zn(II) ions near the coordination geometry of Dy(III) ion in 6-Dy is likely to keep the first excited m_J levels significantly away from the ground state m_J level and is responsible for the observation of zero field slow magnetic relaxation behavior. The data collected in the presence of a magnetic field of H_dc = 2 kOe enhances the energy barrier by two-fold (88.63 K, τ₀ = 1.36 × 10^-7 s) in 6-Dy, suggesting the presence of QTM at zero field along with other under barrier relaxations, such as the Raman process. On the other hand, complex 2-Ce shows field induced slow relaxation of magnetization behavior with an effective energy barrier of 12.24 K (τ₀ = 1.89 × 10^-4 s). The CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations using MOLCAS 8.0 code further rationalized our experimentally observed magnetization dynamics.

Four mononuclear dysprosium complexes with neutral Schiff-base ligands: syntheses, crystal structures and slow magnetic relaxation behavior

Four mononuclear 9-coordinate Dy-based complexes, [Dy(HL¹)₂(NO₃)₃(CH₃OH)] (1Dy), [Dy(HL²)₂(NO₃)₃(H₂O)] (2Dy), [Dy(HL³)₃(NO₃)₃]·CH₃CN (3Dy), and [Dy(HL⁴)₃(NO₃)₃] (4Dy), have been constructed by neutral Schiff-base ligands (1-[N-(4-R)aminomethylidene-2(1H)-naphthalenone, R = -Cl (HL¹), -NO₂ (HL²), -OCH₃ (HL³), -I (HL⁴)). By tuning the terminal substituent group of HL ligands, the number of HL ligands coordinated to the central Dy³⁺ ion unexpectedly varies from 2 to 3, and the local symmetry around the Dy³⁺ ion reduces from D_3h to C_s. Magnetic measurements reveal that 2Dy can display single-ion magnet (SIM) behavior in zero dc field, while 1Dy, 3Dy and 4Dy show field-induced slow magnetic relaxation. Ab initio calculations were employed to elucidate magnetic anisotropy in the complexes, including g-tensors, averaged transition magnetic moments and magnetic easy axes. The difference in magnetic behaviors of the four complexes can be ascribed to the terminal substituent effect of neutral Schiff-base ligands.

Slow relaxation of Dy(III) single-ion magnets dominated by the simultaneous binding of chelating ligands in low-symmetry ligand-fields

Electronic effect and geometry distortion of low-symmetry ligand-field on the anisotropy barrier (U_eff) of spin reversal have been compared in three Dy(III) single-ion magnets through the simultaneous binding of chelating ligands. The substitution of N,O-salicylaldoxime by N,N'-1,10-phenanthroline in the distorted triangular-dodecahedronal field sharply decreases the U_eff by 286 K due to an increase in non-preferred transverse anisotropy, while the geometry distortion with CShM = 1.569 went down to 1.376 only lowering the U_eff by 12 K. The co-coordination strategy of heterodonor ligands highlights the importance of ligand-surroundings on the relaxation dynamics.

Macrocycle supported dimetallic lanthanide complexes with slow magnetic relaxation in Dy2 analogues

Six dimetallic lanthanide complexes, [Ln2(L')(acac)4] (1Dy-3Gd) (Ln = Dy (1Dy), Tb (2Tb) and Gd (3Gd)) and [Ln2(L')(tfac)4] (4Dy-6Gd) (Ln = Dy (4Dy), Tb (5Tb) and Gd (6Gd)) (H2L' = 1,9-dichloro-3,7,11,15-tetraaza-1,9(1,3)-dibenzenacyclohexadecaphane-2,10-diene-1,9-diol), have been synthesized by the reaction of lanthanide nitrates with the HL ligand in the presence of acetylacetonate (acac) (or trifluoroacetylacetonate (tfac) and triethylamine (HL = 4-chloro-2,6-bis(-((3-((3-(dimethylamino)propyl)amino)propyl)imino)methyl)phenol). Ln-Assisted modification of the Schiff base HL occurred and led to the formation of a new macrocyclic ligand (H2L'). X-ray crystallographic analysis revealed that the LnIII ions of complexes 1Dy-6Gd are all eight-coordinated in a square antiprismatic geometry with D4d local symmetry. Magnetic measurements of these complexes revealed that 1Dy and 4Dy show single-molecule magnet behaviour with energy barriers of 66.7 and 79.0 K, respectively, under a zero direct magnetic field. The orientations of the magnetic axes and crystal field parameters were obtained from theoretical calculations and an electrostatic model. The magneto-structural correlations of SMMs 1Dy and 4Dy are further discussed in detail.

Dinuclear lanthanide–lithium complexes based on fluorinated β-diketonate with acetal group: magnetism and effect of crystal packing on mechanoluminescence

A convenient and straightforward synthesis of a novel type of Ln–Li β-diketonates with a discrete molecular structure is presented.

Modulation of the directions of the anisotropic axes of DyIII ions through utilizing two kinds of organic ligands or replacing DyIII ions by FeIII ions

Two complexes based on Dy₄ or Fe₂Dy₂ tetrahedral unit have been obtained by employing mixed organic ligands. The directions of the easy magnetization for the Dy^III in both complexes were successfully modulated.

Syntheses, structures and magnetic properties of macrocyclic Schiff base-supported homodinuclear lanthanide complexes

Five new homodinuclear lanthanide complexes with the general formula [(acac)4Ln2(L)] (Ln3+ = Dy3+ (1), Tb3+ (2), Ho3+ (3), Er3+ (4), and Gd (5)) were synthesized by one-pot [2 + 2] condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane in the presence of various lanthanide acetylacetonates. The eight-coordinate Ln(iii) centre adopts a slightly distorted square antiprism geometry with D4d symmetry. Theoretical analysis and magnetic measurements reveal that the corresponding Dy complex 1 exhibits slow magnetic relaxation behavior, characteristic of a typical SMM with the intramolecular ferromagnetic Dy3+Dy3+ interaction.

Single-ion magnets with D4d symmetry based on electron-donating β-diketonate Dy(iii) complexes

Four single-ion magnets based on electron-donating β-diketonate Dy(iii) complexes have been designed and isolated to explore the magnetism–structure relationship.

Half-sandwich lanthanide crown ether complexes with the slow relaxation of magnetization and photoluminescence behaviors

Four half-sandwich lanthanide crown ether complexes were successfully synthesized and structurally characterized. Dysprosium complexes show both the slow relaxation of magnetization and photoluminescence behaviors.

Asymmetry-unit-dominated double slow-relaxation modes of 2,6-dimethyl-3,5-heptanedione dysprosium SMMs

Two new β-diketone mononuclear dysprosium complexes exhibit two types of single and double relaxation modes under optimized DC field.