Enhancing the single-molecule magnetic performance of β-diketonate Dy(III) complexes by modulating the coordination microenvironment and magnetic interaction: from a mononuclear to a dinuclear structure

Based on a β-diketonate ligand, a mononuclear Dy(III) complex, [Dy(dmpd)3(bpy)] (1) (dmpd = 4,4-dimethyl-1-phenylpentane-1,3-dione, bpy = 2,2'-dipyridyl), of [DyN2O6] type has been synthesized with a capping nitrogen-containing coligand. Then, a dual capping coligand 2,2'-bipyrimidine (bmp) is introduced to be a bridge to link two β-diketonate-Dy(III) motifs, leading to a new dinuclear Dy(III) complex, [Dy2(dmpd)6(bmp)] (2). Dy(III) centers in both complexes feature an N2O6 octacoordinated environment with an approximate square-antiprism geometry (D4d). Without a dc field, the SMM behaviour is absent in complex 1, but can be clearly observed in dinuclear 2 with a Ueff of 87.29 K. The significantly improved magnetism arising in 2 is mainly due to the modulation of the coordination environment around the Dy(III) ions and the superexchange magnetic interactions inside the dinuclear units, thus allowing for the effective inhibition of the quantum tunneling of magnetization at low temperatures and promotion of the uniaxial magnetic anisotropy. For 1, a diamagnetic Y(III) analogue [Y(dmpd)3(bpy)] (3) and diluted sample 1@Y were constructed to further perform the dilution experiment, coupled with theoretical calculations further supporting that the synergetic contributions of intermolecular dipole-dipole interactions, intramolecular coupling and uniaxial magnetic anisotropy cause the enhancement of dynamic magnetic relaxation.

Toward liquid cell quantum sensing: Ytterbium complexes with ultranarrow absorption

The energetic disorder induced by fluctuating liquid environments acts in opposition to the precise control required for coherence-based sensing. Overcoming fluctuations requires a protected quantum subspace that only weakly interacts with the local environment. We report a ytterbium complex that exhibited an ultranarrow absorption linewidth in solution at room temperature with a full width at half maximum of 0.625 milli-electron volts. Using spectral hole burning, we measured an even narrower linewidth of 410 pico-electron volts at 77 kelvin. Narrow linewidths allowed low-field magnetic circular dichroism at room temperature, used to sense Earth-scale magnetic fields. These results demonstrated that ligand protection in lanthanide complexes could substantially diminish electronic state fluctuations. We have termed this system an "atomlike molecular sensor" (ALMS) and proposed approaches to improve its performance.

Redox-Induced Intramolecular C-C Coupling of Acyclic Bis(2-pyridylmethylene)ethylenediamine on a Ru(acac)2 Platform

The paper documents redox-triggered C-C coupling of acyclic N,N'-bis(2-pyridylmethylene)ethylenediamine (BPE) to yield 2,3-bis(2-pyridyl)pyrazine (DPP) upon coordination to an electron-rich {Ru(acac)₂} (acac = acetylacetonate) unit. This led to DPP-bridged [{Ru(acac)₂}₂(DPP)]^0/+ (2 and [2]ClO₄) along with the unperturbed BPE-bridged [{Ru(acac)₂}₂(BPE)] (1). On the contrary, electron-poor {Ru(Cl)(H)(CO)(PPh₃)₃} yielded BPE-bridged [3](ClO₄)₂ as an exclusive product. Synergistic metal (Ru)-ligand (BPE) redox participation toward chemical noninnocence of the Schiff base ligand and DPP-mediated electronic communication in Ru^IIRu^III-derived [2]ClO₄ are addressed.

Electrochemical Exploration of Active Cu-Based Atom Transfer Radical Polymerization Catalysis through Ligand Modification

The intersection between Cu-catalyzed atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP) has been recently shown to be a result of competition between the Cu^I and Cu^II complexes of polyamine ligands for the same organic free radical. The tetradentate ligands N,N'-bis-2'-pyridylmethyl-ethane-1,2-diamine (L¹) and N,N'-dimethyl-N,N'-bis-2'-pyridylmethyl-ethane-1,2-diamine (L²) form stable Cu complexes which, depending on their oxidation state, can either liberate or complex organic radicals. Herein, we show that this process may be affected by subtle changes to the ligand system. Switching from a tertiary amine (L²) to a secondary amine (L¹) retains ATRP and OMRP activity through a series of cyclic voltammetry measurements in the presence of the initiator bromoacetonitrile.

Magnetic anisotropy in YbIII complex candidates for molecular qubits: a theoretical analysis

The magnetic properties of mononuclear YbIII complexes have been explored by using multiconfigurational CASPT2/RASSI calculations. Such complexes, in particular the case of [Yb(trensal)] complex, have been proposed as molecular qubits due to their spin dynamics properties. We have verified the accuracy of the theoretical approach to study such systems by comparing with experimental magnetic data. In order to have a wide overview of the magnetic properties of mononuclear YbIII complexes, we have considered simple charged and neutral models, [Yb(H2O)n]3+ and [Yb(OH)3(H2O)n-3], for many coordination modes. Thus, the results for more than 100 models allow extraction of some conclusions about the best ligand distributions in the coordination sphere to tailor the magnetic properties. Some low coordination, between 3 and 5, complexes that have no experimental magnetic data have been studied computationally to check if they can present high magnetic anisotropy.

Lanthanide-Based Single-Molecule Magnets Derived from Schiff Base Ligands of Salicylaldehyde Derivatives

The breakthrough in Ln(III)-based SMMs with Schiff base ligands have been occurred for the last decade on account of their magnetic behavior, anisotropy and relaxation pathways. Herein, we review the synthetic strategy, from a structural point of view and magnetic properties of mono, di, tri and polynuclear Ln(III)-based single-molecule magnets mainly with Schiff bases of Salicylaldehyde origin. Special attention has been given to some important breakthroughs that are changing the perspective of this field with a special emphasis on slow magnetic relaxation. An overview of 50 Ln(III)-Schiff base complexes with SMM behavior, covering the period 2008–2020, which have been critical in understanding the magnetic interactions between the Ln(III)-centers, are presented and discussed in detail.

Magnetic dynamics of an open-ring tridysprosium complex employing mixed ligands

By employing mixed ligands, a new trinuclear dysprosium complex [Dy3(dbm)3(L)4](ClO4)2·CH2Cl2·2MeOH (1, Hdbm = dibenzoylmethane; HL = 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol) was synthesized by a one-pot reaction. According to structural characterization, all the 8-coordinated Dy(iii) sites are well arranged with slightly distorted square antiprism (D4d) geometries. Magnetic measurements reveal that 1 exhibits typical single-molecule magnetic behavior at zero magnetic field and shows rarely open hysteresis loops up to 3 K among open-ring {Dy3} SMMs, where the relaxation time remains very stable under the protection from the Dy-Dy magnetic coupling in the open-ring arrangement of Ising spins.

Dinuclear Lanthanide(III) Complexes Showing Single-Molecule Magnet Behaviour and Optical Properties

Three dinuclear lanthanide(iii) complexes with an acetate bridge, which are synthesised by a Salen-type Schiff base and β-diketonate ligands, i.e. [Ln2L2(TTA)4(OAc)2]·CH2Cl2 (Ln=Eu (1), Gd (2), Dy (3); TTA=thenoyltrifluoroacetonate, H2L=N,N′-ethylenebis(salicylideneimine), are investigated. We obtained the structures of complexes 1–3 by X-ray crystallography. Notably, in terms of the structure of these complexes, what is intriguing is that the acetate groups link two Lniii ions, whereas the cadmium ions do not coordinate. Lanthanide-based luminescence is exhibited by complex 1, which exists in both the solid state and a methanol solution. Through magnetic analysis, it is found that a field-induced single-molecule magnet behaviour is exhibited by complex 3, and the energy barrier is shown to be Ueff=45.97K.

Coumarin-lanthanide based compounds with SMM behavior and high quantum yield luminescence

Coumarin-based lanthanide complexes of general formula [Ln(coum)3(phen)(H2O)x]·yH2O (Ln-phen, x = 0,1, 0 ≤ y ≤ 1.5; phen = 1,10-phenanthroline; coum = 3-acetyl-4-hydroxylato-coumarin; Ln = Eu, Tb, Dy, Tm) and [Ln(coum)3(batho)]·0.7EtOH (Ln-batho, batho = 4,7-diphenyl-1,10-phenanthroline; Ln = Eu, Tb, Dy, Tm) were synthesized. The magnetic relaxation and photoluminescence behavior of these complexes was compared with that of the related compounds [Ln(coum)3(EtOH)(H2O)]·EtOH (Ln-coum), so as to investigate the effects of incorporating a second chromophore, either the phen or batho ligand, to the original coordination scaffold, provided with three coumarin (coum) ligands. Slow relaxation of the magnetization under H = 0 with moderate activation energies was observed for the Dy-phen (U/kB = 99.1 K) and Dy-batho (U/kB = 67.1 K) compounds, whereas Tb analogues presented field-induced single molecule magnet (SMM) behavior, with U/kB = 11.7 K (16.6 K@3 kOe) for Tb-phen (Tb-batho), respectively. Luminescent emission in the visible range was observed for all the Ln-coumarin based compounds upon ligand sensitization, with high quantum yields of 45 (40%) for Eu-phen (Eu-batho) compounds and 65-76-58% for Tb-coum, phen, batho analogues. Sensitization is mainly provided by the coumarin ligand having the energy difference ΔE between its triplet state T1 and the lanthanide emitting level closest to the optimum, while the second ligand can play either a synergistic or competing sensitizing role. The Tb-phen/batho compounds presented simultaneously SMM and luminescent behavior, with excellent values of the bifunctional figure of merit (ηSMM-QY ∼ 1000% K). The reported compounds represent a new class of bifunctional materials with potential interesting application in various fields.

Wheel-like 6 luminescent lanthanide complexes covering the visible and near-infrared domains

Luminescence properties of wheel-like lanthanide complexes.

Substituent effects of auxiliary ligands in mononuclear dibenzoylmethane DyIII/ErIII complexes: single-molecule magnetic behavior and luminescence properties

The single-molecule magnetic behavior and luminescence of [(dbm)₃Ln(dmbipy)] and [(dbm)₂Ln(dmobipy)(NO₃)] are significantly modified by replacing the substituents of auxiliary ligands.

Strong intramolecular DyIII–DyIII magnetic couplings up to 15.00 cm−1 in phenoxyl-bridged dinuclear 4f complexes

Unexpectedly, intramoleular Dy^III–Dy^III magnetic couplings are up to 15.00 cm⁻¹ in the phenolate-bridged Dy₂ complexes. And single-molecule magnet behavior is exhibited with effective energy of 76.18 K under zero dc field.

The near-infrared luminescence and magnetism of dinuclear complexes with different local symmetries constructed from a β-diketonate co-ligand and bis-Schiff base ligand

A Dy^III-complex based on a β-diketonate co-ligand and bi-Schiff base ligand displays slow magnetic relaxation behavior.

A family of planar hexanuclear CoLn clusters with lucanidae-like arrangement and single-molecule magnet behavior

A family of planar hexanuclear CoLn clusters with the hydroxyl and nitrogen rich ligand 2-[bis(pyridin-2-ylmethyl) amino]-2-(hydroxymethyl)propane-1,3-diol (H₃L), formulated as [Co₄Ln₂(μ₃-O)₂(μ-N₃)₂(OH)₂(H₂O)₂(HL)₄]·(CH₃CO₂)₂·20H₂O [Ln = Dy (1), Gd (2), Tb (3), Eu (4) and Ho (5)], have been synthesized and structurally characterized. They are isomorphous and feature a lucanidae-like arrangement. They are the first examples of 3d-4f clusters with the H₃L ligand. In addition, the magnetic properties of 1-5 have been investigated and the single-molecule magnet (SMM) behaviour is observed for 1.

Evidencing under-barrier phenomena in a Yb(iii) SMM: a joint luminescence/neutron diffraction/SQUID study

The synthesis, spectroscopic and magnetic characterisation and ab initio investigation of a new Yb based complex, [YbTp₂NO₃], are reported and exploited to rationalise its field-induced SMM behaviour.

Improved luminescence properties by the self-assembly of lanthanide compounds with a 1-D chain structure for the sensing of CH3COOH and toxic HS− anions

A family of lanthanide compounds has been explored and enhanced luminescence has been accomplished by doping method. A brand new and multifunctional fluorescence probe was developed, which was able to detect CH₃COOH and HS⁻ with different mechanisms.

Enhanced luminescence for detection of small molecules based on doped lanthanide compounds with a dinuclear double-stranded helicate structure

A family of isostructural lanthanide compounds was explored and enhanced luminescence accomplished by doping. A novel and multifunctional fluorescence probe was developed, which was able to detect CH₃COOH, Al³⁺ and Cr₂O₇²⁻.

Solvent-tuned magnetic exchange interactions in Dy2 systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)]₂ (1), [Dy(api)]₂·2CH₂Cl₂ (2), [Dy(Clapi)]₂·2C₄H₈O (3), and [Dy(Clapi)]₂·2C₃H₆O (4) (H₃api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H₃Clapi = 2-(2′-hydroxy-5′-chlorophenyl)-1,3-bis[3′-aza-4′-(2′′-hydroxy-5′′-chlorophenyl)prop-4′-en-1′-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H₃api/H₃Clapi with DyCl₃·6H₂O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N₄O₃) to encapsulate a Dy^III ion and all of the Dy^III centers in 1–4 adopt a distorted square antiprism geometry with D_4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2–4 showed filed-induced slow magnetic relaxation with barriers U_eff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1–4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the Dy^III ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the U_eff values. The different lattice solvents influence Dy–O–Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.

Solvent-tuning changes the magnetic exchange interaction and results in different magnetic relaxation dynamics in Dy₂ systems ligated by a μ-phenolato heptadentate Schiff base.

Versatile coordinating abilities of acyclic N4 and N2P2 ligand frameworks in conjunction with Sn[N(SiMe3)2]2

The conjoint effort of the –CH₂–CH₂– linker backbone and coordinating sites in the tetradentate ligand stabilizes a variety of stannylenes.

Lanthanoid complexes supported by retro-Claisen condensation products of β-triketonates

β-Triketonates have been recently used as chelating ligands for lanthanoid ions, presenting unique structures varying from polynuclear assemblies to polymers. In an effort to overcome low solubility of the complexes of tribenzoylmethane, four β-triketones with higher lipophilicity were synthesised. Complexation reactions were performed for each of these molecules using different alkaline bases in alcoholic media. X-ray diffraction studies suggested that the ligands were undergoing decomposition under the reaction conditions. This is proposed to be caused by in situ retro-Claisen condensation reactions, consistent with two examples that have been reported previously. The lability of the lanthanoid cations in the presence of a varying set of potential ligands gave rise to structures where one, two, or three of the molecules involved in the retro-Claisen condensation reaction were linked to the lanthanoid centres. These results, along with measurements of ligand decomposition in the presence of base alone, suggest the solvent used will modulate the impact of the retro-Claisen condensation in these complexes.

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.

Anion-driven structures and SMM behavior of dinuclear terbium and ytterbium complexes

SMM behavior is observed for [Ln₂(HL)₄(NO₃)₆] (Ln = Tb and Yb, HL = 8-hydroxyquinaldine) complexes having nine-coordinated lanthanide centres, whereas, [Ln₂(HL)₄Cl₆]·2EtOH complexes, having hexa-coordinated lanthanide centres do not show any SMM property.