Magnetic anisotropy in octahedral Dy(III) and Yb(III) complexes

New organophosphate complexes [Ln(dippH)3(dippH2)3]·(H2O)6, (Ln = Dy, Yb and Y; dippH2 = 2,6-diisopropylphenyl phosphate), displaying octahedral coordination geometry around the metal ion, exhibit unusual slow relaxation of magnetisation, which is investigated through experimental studies and ab initio CASSCF calculations.

Novel stable ytterbium acetylacetonate-quinaldinate complexes as single-molecule magnets and surprisingly efficient luminophores

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q-) ligand, namely 1D-polymeric [Yb(acac)2(Q)]n (1, acac- is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)2(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb3+. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C-H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q- thereby decreasing the energy of coordinating C-O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.

Magnetic anisotropy of transition metal and lanthanide ions in pentagonal bipyramidal geometry

The magnetic anisotropy associated with a pentagonal bipyramidal (PBP) coordination sphere is examined on the basis of experimental and theoretical investigations. The origin and the characteristics of this anisotropy are discussed in relation to the electronic configuration of the metal ions. The effects of crystal field, structural distortion, and a second-coordination sphere on the observed anisotropies for transition meal and lanthanide ions are outlined. For the Ln derivatives, we focus on compounds showing SMM-like behavior (i.e. slow relaxation of their magnetization) in order to highlight the essential chemical and structural parameters for achieving strong axial anisotropy. The use of PBP complexes to impart controlled magnetic anisotropy in polynuclear species such as SMMs or SCMs is also addressed. This review of the magnetic anisotropies associated with a pentagonal bipyramidal coordination sphere for transition metal and lanthanide ions is intended to highlight some general trends that can guide chemists towards designing a compound with specific properties.

Modulating the Structures and Magnetic Properties of Dy(III) Single-Molecule Magnets through Acid-Base Regulation

Chemical modulation on the structures and physical properties of the coordination complexes is of great interest for the preparation of new functional materials. By changing the acidity or basicity of the reaction medium, the deprotonation degree of a multidentate ligand with multiple active protons, H₄daps (H₄daps = N',N'″-((1E,1'E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(2-hydroxybenzohydrazide)), can be regulated on purpose. With this ligand of different deprotonation and charges, three new Dy^III complexes ([Dy(H₃daps)(CH₃COO)₂(EtOH)]·CH₃COOH (1Dy), [Dy₂(H₂daps)₂(EtOH)₂(H₂O)₂(MeOH)₂](CF₃SO₃)₂·(H₂O)₂ (2Dy), and [Dy₃(H₁daps)₂(H₂daps)(μ₃-OH)(EtOH)(H₂O)] (3Dy)) of different nuclearities (mono-, di-, and trinuclear for 1Dy to 3Dy, respectively) have been synthesized and characterized structurally and magnetically. Analyses on the related bond lengths and resulting hydrogen bond modes in the complexes provide the details of the deprotonation position and the charge of the ligands, which can be in the form of H₃daps^-, H₂daps^2-, and H₁daps^3-. Interestingly, the more deprotonated ligand can act as a bridging ligand between the Dy^III centers using the phenol and/or carbonyl oxygen atoms, which leads to the multinuclear structures. Magnetic studies on these complexes revealed that complex 1Dy is a field-induced single-molecule magnet (SMM), while complexes 2Dy and 3Dy show SMM behavior under a zero dc field.

Slow magnetic relaxation of mononuclear complexes based on uncommon Kramers lanthanide ions CeIII, SmIII and YbIII

Based on uncommon Kramers ions CeIII, SmIII and YbIII, complexes [Ce(dppbO2)2Cl3] (1, dppbO2 = 1,2-bis(diphenylphosphino)benzene dioxide), [Sm(dppbO2)2Cl3] (2) and [Yb(dppbO2)2Cl2]Cl (3) toward single-ion magnets were obtained and fully characterized. Complexes...

Successive syntheses and magnetic properties of homodinuclear lanthanide macrocyclic complexes

A series of homodinuclear β-diketone lanthanide(III) complexes, formulated as [(acac)₄Ln₂(L1)] (Ln³⁺ = Dy³⁺ (1), Tb³⁺ (2), and Gd³⁺ (3), respectively) were first synthesized based on a closed-macrocyclic ligand (H₂L1) derived from the [2 + 2] cyclocondensation of 4-tert-butyl-2,6-diformylphenol and o-phenylenediamine in the presence of lanthanide acetylacetonates. Subsequently, by using the above compounds as building blocks to assemble directly with another Schiff base ligand, N,N'-bis(5-chlorosalicylidene)-o-phenylenediamine (H₂L2), three new homodinuclear sandwich-type lanthanide complexes with the general formula [Ln₂(L1)(L2)₂] (Ln³⁺ = Dy³⁺ (4), Tb³⁺ (5), and Gd³⁺ (6), respectively) were further designed and prepared. Single-crystal X-ray analyses show that the central Ln³⁺ ion adopts a distorted square antiprism conformation with D_4d local symmetry. Magnetic studies reveal ferromagnetic interaction between Dy³⁺ and Tb³⁺ centres and zero-field slow relaxation of magnetization for Dy complexes 1 and 4. The corresponding magneto-structural correlations of SMMs 1 and 4 were further discussed by theoretical calculations and with experimental outcomes.

Assembly of tetra-nuclear YbIII-containing selenotungstate clusters: synthesis, structures, and magnetic properties

Two tetra-nuclear Yb^III-incorporated selenotungstate clusters, Keggin (C₂H₈N)₆Na₁₄[Yb₄Se₆W₄₄O₁₆₀(H₂O)₁₂]·40H₂O (1) and Wells-Dawson (C₂H₈N)₄Na₁₄[Yb₄Se₆W₄₅O₁₅₉(OH)₆(H₂O)₁₁]·38H₂O (2), have been isolated through a pH-controlled assembly, which exhibit the first Yb^III-containing polyoxotungstates with selenium heteroatoms. Their assemblies rely on the structure-directing effects of SeO₃^2- anion templates to give rise to available Se-containing Keggin-/Wells-Dawson-type motifs. Both compounds were characterized by single-crystal X-ray diffraction, IR spectroscopy, power X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) as well as electrospray ionization mass spectrometry (ESI-MS). Furthermore, systematic magnetic studies revealed that 1 exhibits field-induced single-molecule magnetic behavior with a pre-exponential factor of τ₀ = 6.60(7) × 10^-8 s and a relaxation energy barrier of ΔE/k_B = 39.44(2) K, while 2 only displays antiferromagnetic interactions between the ytterbium centers.

Strong Equatorial Crystal Field Enhances the Axial Anisotropy and Energy Barrier for Spin Reversal Process in Yb2 Single Molecule Magnets

The importance of equatorial crystal fields on magnetic anisotropy of ytterbium single molecule magnets (SMMs) is observed for the first time. Herein, we report three similar dinuclear ytterbium complexes with the formula [Yb₂ (3-OMe-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF (1), [Yb₂ (3-H-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF⋅H₂ O (2), and [Yb₂ (3-NO₃ -L)₂ (DMF)₂ (NO₃ )₂ ] (3), [where 3-X-H₂ L=N'-(2-hydroxy-3-X-benzylidene)picolinohydrazide, X=OMe (1), H (2) NO₂ (3)]. Detailed magnetic measurements reveal the presence of weak antiferromagnetic interactions between the Yb centers and a field-induced slow relaxation of magnetization in all complexes. A higher energy barrier for spin reversal was observed for complex 1 (U_eff =50 K) and it decreases in the order of 2 (47 K) to 3 (40 K). Notably, complex 1 shows a remarkable energy barrier within the frequency range of 1-850 Hz reported for Yb-based SMMs. Further, ab initio calculations show a higher axial anisotropy and lower quantum tunneling of magnetization (QTM) in the ground state for 1 compared to 2 and 3. It was also observed that the presence of a strong crystal field in the equatorial plane (when the ∡ O1-Yb-O3 bond angle is close to 90°) enhances the axial anisotropy and improves the SMM behavior in the studied complexes. Both the experimental and theoretical analysis of relaxation dynamics discloses that Raman and QTM play major role on slow relaxation process for all complexes. To provide more insight into the exchange interactions, broken-symmetry DFT calculations were performed.

A seven-coordinated DyIII single-ion magnet with C2v symmetry constructed by a multidentate Schiff-base ligand

Utilizing a flexible Schiff-base ligand with large steric hindrance helps to stabilize the seven-coordinated Ln^III complexes; Dy^III complex with C_2v low symmetry still displays the SIM behavior.

Slow magnetic relaxation in O–Se–O bridged manganese(iii) Schiff base complexes

Two new chain complexes consisting of a Mn(salen) building block bridged by O–Se–O units, [Mn₂(salen)₂(L)](ClO₄) (1) and {[Mn(salen)]₂(L)₂}·Y (2) (salen = N,N′-bis(salicylidene)-ethylenediamine, L = 3,4,5-trifluorobenzeneseleninic acid, Y = salicylaldehyde) have been synthesized and characterized structurally and magnetically.

Field-induced slow magnetic relaxation and luminescence thermometry in a mononuclear ytterbium complex

A mononuclear pentagonal bipyramidal Yb^III complex functions as a field-induced SIM luminescent thermometer.

Controllable syntheses and magnetic properties of novel homoleptic triple-decker lanthanide complexes

A class of novel triple-decker lanthanide complexes have been continuously designed and synthesized based on a Schiff base ligand Cl-salphenH₂ and precursors [(acac)₄Ln₂(L)]. The results reveal Dy complex behaves as a typical SMM with intermetallic ferromagnetic interaction.

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.

Enriching lanthanide single-ion magnetism through symmetry and axiality

Rapidly growing modern information technology demands energy and cost efficient tools that can efficiently store and process a large amount of data. However, the miniaturization technology that was being used to boost the performance of the electronic devices, keeping up with the pace as estimated by Moore's law, is reaching its limit. To overcome these challenges, several alternative routes that can eventually mimic the modern electronics fabrication using silicon have been proposed. Single molecule magnets (SMMs), being considered as one of the potential alternatives, have gone through significant progress and the focus has shifted from the use of polynuclear clusters to mononuclear complexes in the last few years. The recent frenzy in the field of SMMs is driven by a better understanding of the effects of crystal field (CF) and molecular symmetry on the magnetic properties, especially in the case of mononuclear paramagnetic complexes, apart from other controlling factors. This has led to the advent of highly anisotropic single-ion magnets (SIMs) with magnetic blocking temperatures as high as 60 K and anisotropic energy barriers over 1800 K. This article overviews our recent research in the light of the emergence of the importance of CF and symmetry in 4f ion based single-ion magnets (SIMs), especially in the context of SIMs with D5h symmetry, apart from commenting on the synthetic efforts adopted to place these metal ions in unusual coordination geometries.

New field-induced single ion magnets based on prolate Er(iii) and Yb(iii) ions: tuning the energy barrierUeffby the choice of counterions within an N3-tridentate Schiff-base scaffold

Counterions modulate the structure and magnetic properties of rarely observed high-coordinate SIM species.

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.