Synthesis, Structure, Magnetic and Photoluminescent Properties of Dysprosium(III) Schiff Base Single-Molecule Magnets: Investigation of the Relaxation of the Magnetization

Combined experimental and theoretical studies on a series of mononuclear LnIII single-molecule magnets: dramatic influence of remote substitution on the magnetic dynamics in Dy analogues

A series of Ln^III complexes of general formula [Ln(H₂L¹)₂(NO₃)₂(H₂O)](NO₃) (1-5) [Ln = Dy (1), Tb (2) Ho (3), Er (4), and Yb (5)] and an analogous Dy^III complex with ligand H₂L², [Dy(H₂L²)₂(NO₃)₃(H₂O)](NO₃) (6), where H₂L¹ and H₂L² stand for (E)-2-[(2-hydroxyphenyl)iminomethyl]-6-methoxy-4-methylphenol and (E)-2-[(2-hydroxy-5-methylphenyl)iminomethyl]-6-methoxy-4-methylphenol, respectively, have been synthesized and magneto-structurally characterized. All these complexes are isostructural and isomorphous, in which the zwitterionic form of the ligands predominantly coordinate the metal centers. The magnetic study revealed that complex 3 displays negligible SMM behaviour, while 1 and 6 are zero field SMMs, the performance of which can largely be improved in the presence of an applied dc field by lowering under barrier relaxation processes, and finally 2, 4, and 5 are field-induced SMMs. The most remarkable observation in the present study is the dramatically-enhanced SMM performance in 6 compared to 1, achieved by only a remote methyl substitution at the ligand framework to increase the intermolecular separation. Although SINGLE_ANISO ab initio calculations for 1 and 6 are very similar, the POLY_ANISO module revealed weak dipolar interactions in both the compounds but significant antiferromagnetic interaction in 1, thereby justifying the experimental fact. The present work discloses that even a small substitution such as a methyl group can adequately increase the intermolecular separation, leading to several-fold enhanced effective energy barrier.

Three angular Zn2Dy complexes showing the effect of remote coordination at Zn and counter ions on slow magnetic relaxation at Dy centres

Three isostructural Zn2Dy complexes displaying the effect of remote coordination at Zn and counter ions on slow magnetic relaxation at Dy centres.

Bis(η5-cyclo-penta-dien-yl)(2-{[(2-meth-oxy-phen-yl)imino]-meth-yl}phenolato-κ3 O,N,O')terbium

The air- and moisture-sensitive title compound, [Tb(C5H5)2(C14H12NO2)], was synthesized from tris-(cyclo-penta-dien-yl)(tetra-hydro-furan)-terbium and 2-{[(2-meth-oxy-phen-yl)imino]-meth-yl}phenol. Each Tb atom is coordinated by two cyclo-penta-dienyl ligands in an η5-coordination mode and by one N and two O atoms of the organic ligand in a tridentate κ3 O,N,O'-mode.

The first exploration of coordination chemistry using a methyl substituted o-vanillin based ligand: an example starting with Dy4/Zn2Dy2 systems displaying slow relaxation of magnetization

Two butterfly-shaped Dy4 and Zn2Dy2 complexes displaying slow relaxation of magnetization have been synthesized from a new methyl substituted o-vanillin based ligand, enlarging the scope for finding better SMMs.

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 the Magnetization in Anilato-Based Dy(III) 2D Lattices

The search for two- and three-dimensional materials with slow relaxation of the magnetization (single-ion magnets, SIM and single-molecule magnets, SMM) has become a very active area in recent years. Here we show how it is possible to prepare two-dimensional SIMs by combining Dy(III) with two different anilato-type ligands (dianions of the 3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone: C₆O₄X₂²⁻, with X = H and Cl) in dimethyl sulfoxide (dmso). The two compounds prepared, formulated as: [Dy₂(C₆O₄H₂)₃(dmso)₂(H₂O)₂]·2dmso·18H₂O (1) and [Dy₂(C₆O₄Cl₂)₃(dmso)₄]·2dmso·2H₂O (2) show distorted hexagonal honeycomb layers with the solvent molecules (dmso and H₂O) located in the interlayer space and in the hexagonal channels that run perpendicular to the layers. The magnetic measurements of compounds 1, 2 and [Dy₂(C₆O₄(CN)Cl)₃(dmso)₆] (3), a recently reported related compound, show that the three compounds present slow relaxation of the magnetization. In compound 1 the SIM behaviour does not need the application of a DC field whereas 2 and 3 are field-induced SIM (FI-SIM) since they show slow relaxation of the magnetization when a DC field is applied. We discuss the differences observed in the crystal structures and magnetic properties based on the X group of the anilato ligands (H, Cl and Cl/CN) in 1–3 and in the recently reported derivative [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (4) with X = Br, that is also a FI-SIM.