Manipulating the Relaxation of Quasi- D4 d Dysprosium Compounds through Alternation of the O-Donor Ligands

Toroidal versus centripetal arrangement of the magnetic moment in a Dy4 tetrahedron

Magnetic investigation and ab initio calculations reveal toroidal arrangement of the magnetic moment rather than centripetal anisotropies in a tetrahedral Dy4 complex.

The interpretation and prediction of lanthanide single-ion magnet from ab initio electronic structure calculation: The capability and limit

Single-molecule magnet (SMM) is a fascinating system holding the potential of being revolutionary micro-electronic device in information technology. However current SMMs are still far away from real-life application due to...

Structural and magnetic studies of six-coordinated Schiff base Dy(III) complexes

With the aim to tune magnetic anisotropies of six-coordinated Dy(III) complexes, four bis-Schiff bases bearing different spacers and one mono-Schiff base were designed, which are bis(2-hydroxylnaphthalenylmethylene)hydrazine (H2L1), bis(2-hydroxylnaphthylmethylene)ethylenediamine (H2L2), bis(2-hydroxylnaphthylmethylene)-propylenediamine...

Macrocycle based dinuclear dysprosium(III) single molecule magnets with local D5h coordination geometry

Targeted approaches for manipulating the coordination geometry of lanthanide ions are a promising way to synthesize high-performance single-molecule magnets (SMMs), but most of the successful examples reported to date focus on mononuclear complexes. Herein, we describe a strategy to assemble dinuclear SMMs with Dy^III ions in approximate D_5h coordination geometry based on pyrazolate-based macrocyclic ligands with two binding sites. A Dy4 complex with a rhomb-like arrangement of four Dy^III as well as two dinuclear complexes having axial chlorido ligands (Dy2·Cl and Dy2*·Cl) were obtained; in the latter case, substituting Cl^- by SCN^- gave Dy2·SCN. Magneto-structural studies revealed that the μ-OH bridges with short Dy-O bonds dominate the magnetic anisotropy of the Dy^III ions in centrosymmetric Dy4 to give a vortex type diamagnetic ground state. Dynamic magnetic studies of Dy4 identified two relaxation processes under zero field, one of which is suppressed after applying a dc field. For complexes Dy2·Cl and Dy2*·Cl, the Dy^III ions feature almost perfect D_5h environment, but both complexes only behave as field-induced SMMs (U_eff = 19 and 25 K) due to the weak axial Cl^- donors. In Dy2·SCN additional MeOH coordination leads to a distorted D_2d geometry of the Dy^III ions, yet SMMs properties at zero field are observed due to the relatively strong axial ligand field provided by SCN^- (U_eff = 43 K). Further elaboration of preorganizing macrocyclic ligands appears to be a promising strategy for imposing a desired coordination geometry with parallel orientation of the anisotropy axes of proximate Dy^III ions in a targeted approach.

Regulating the magnetic properties of seven-coordinated Dy(III) single-ion magnets through the effect of positional isomers on axial crystal-field

Six Dy(III) single-ion magnets (SIMs) [Dy(n-OMe-bbpen)X] were synthesized by a solvothermal reaction with three positional isomers (ortho, meta, and para) of ligands n-OMe-H₂bbpen and dysprosium halides DyX₃, (n-OMe-H₂bbpen = N,N'-bis(2-hydroxy-n-methoxybenzyl)-N,N'-bis(2-methylpyridyl)ethylenediamine; n = 3, X = Cl, 1; n = 3, X = Br, 2; n = 4, X = Cl, 3; n = 4, X = Br, 4; n = 5, X = Cl, 5; n = 5, X = Br, 6). Dynamic magnetic measurements revealed that the six complexes possess notably different effective barriers of magnetic reversal: 872.0 K (1), 1210.1 K (2), 137.9 K (3), 602.6 K (4), 907.0 K (5) and 1216.7 K (6). 6 showed the best performance as SIMs among the six Dy(III) complexes. Moreover, the magnetic hysteresis loops of 6 remained open at 21 K. The crystal structures indicate the switching of local symmetry around Dy(III) ion, aroused by the variation in intermolecular interactions and steric effects. This switch is primarily correlated with the distinction of magnetic properties. In addition, ab initio calculations confirmed that the different electrostatic potential around Dy(III) ion stemming from the electronic effect of the OMe-substituted group is another factor leading to the distinction in magnetic properties. This work warns us that when designing ligands for Dy-SIMs, the effect of positional isomerism on magnetic performance must be considered, which is one of the factors that can easily be overlooked.

Improving the single-molecule magnet properties of two pentagonal bipyramidal Dy3+ compounds by the introduction of both electron-withdrawing and -donating groups

Two mononuclear Dy³⁺ compounds [Dy(bmbpen-F)X] (X = Cl, 1; Br, 2) with a pentagonal bipyramidal (PBP) geometry were obtained from N,N'-bis-(5-methyl-2-hydroxybenzyl)-N,N'-bis(5-fluoro-2-methylpyridyl)ethylenediamine (H₂bmbpen-F) and dysprosium halides. The magnetic anisotropy and single-molecule magnet (SMM) behavior of these PBP compounds were regulated by introducing both electron-withdrawing F atoms into the equatorial pyridine rings and electron-donating -CH₃ groups into the axial phenolic hydroxyl rings. The results of magnetic characterization show that 1 and 2 exhibit single molecule magnet behavior with magnetization reversal barriers of 990(13) and 1189(16) K under a zero dc external field and magnetic hysteresis loops up to 26 K and 36 K, respectively. The results of ab initio calculations are consistent with the experimental observations, confirming that the simultaneous introduction of electron-withdrawing groups into the equatorial positions and electron-donating groups into the axial positions can lead to PBP Dy-SMMs with improved properties.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high‐performing single‐molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.

Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes

Treatment of the new methanediide-methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh2S)2}2-) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)2][Dy(SCS)2(K(DME)2)2] (2Dy), [Dy(SCS)2][Na(DME)3] (3Dy) and [Dy(SCS)2][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)2][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh2NSiMe3)2}2-, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy-5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s-1). Fitting the alternating current magnetic susceptibility data for 2Dy-5Dy gives energy barriers to magnetic relaxation (U eff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy-4Dy join a privileged group of SMMs with U eff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy-4Dy, the Dy-components can be grouped into 2Dy-cation/4Dy and 2Dy-anion/3Dy, where the former have almost linear C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with short average Dy[double bond, length as m-dash]C distances, and the latter have more bent C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with longer average Dy[double bond, length as m-dash]C bonds. Both U eff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M-L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between U eff barrier and axial linearity in structurally comparable systems.

Solvent responses and substituent effects upon magnetic properties of mononuclear DyIII compounds

Solvent responsive magnets comprise a class of molecule-based materials where lattice solvent driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of magnet where single-crystal to single-crystal (SCSC) transformations within mononuclear DyIII compounds result in the switching of DyIII single-molecule magnets (SMMs). This structural transformation involves lattice solvents which leads to significant changes in the color and magnetic properties. Additionally, the relaxation dynamics of mononuclear DyIII compounds are perceptibly fine-tuned by the modification of β-diketonate ligands. The uniaxial magnetic anisotropies, magneto-structural correlations and the relaxation mechanism were investigated by magnetic studies and ab initio calculations. These experimental and theoretical studies indicate that compound 2 exhibits the best magnetic properties in compounds 1-4. The experimental observation is supported by the theoretical prediction of QTM time (τZeeQTM) as theτZeeQTM of 2 is remarkably longer than those of the other three compounds by an order of magnitude. This means that, compared with 1, 3, and 4, the magnetic relaxation of 2 is significantly slower. Meanwhile, 2 has the largest value of axial ESP (the axial electrostatic potential), which supports the smallest gXY value in these compounds, resulting in better SMM properties. The present results offer a systematic synthesis regulation to change the magnetization dynamics and further understand magneto-structural correlations for DyIII SMMs.

In Situ Ligand Formation in the Synthetic Processes from Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds: Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis

Guided by the self-assembled process and mechanism, the strategy of in situ Schiff base reaction would be capable of bringing a feasible method to construct and synthesize lanthanide compounds with distinct structures and magnetic properties. A mononuclear Dy(III) compound was synthesized through a multidentate Schiff base ligand and a chelating β-diketonate ligand, which was named as [Dy(L)(bppd)]·CH₃OH [1; H₂L = N,N'-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and bppd = 3-bis(pyridin-2-yl)propane-1,3-dione]. Furthermore, a new binuclear Dy(III) compound, [Dy₂(H₂Lox)(bppd)₃]·8CH₃OH [2; H₄Lox = N,N'-bis[2-hydroxy-5-methyl-3-(hydroxyiminomethyl)benzyl]-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine], was obtained via an in situ synthetic process. Under similar synthetic conditions, [Dy(L)(ctbd)] [3; ctbd = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione] and [Dy₂(H₂Lox)(ctbd)₃]·CH₃OH·C₄H₁₀O (4) were synthesized by modifying the β-diketonate ligand and in situ Schiff base reaction. Compound 3 is a mononuclear configuration, while compound 4 exhibits a binuclear Dy(III) unit. Therein, formylbenzyl groups of H₂L in 1 and 3 were changed to (hydroxyiminomethyl)benzyl groups in 2 and 4, respectively. In isomorphous 2 and 4, two Dy(III) centers are connected through two phenol O^- atoms of the H₂Lox^2- ligand to form a binuclear structure. Eight-coordinated Dy(III) ions with different distortions can be observed in 1-4. The crystals of 1 and 3 suffered dissolution/precipitation to obtain 2 and 4, respectively. The relationship between the structure and magnetism in compounds 1-4 was discussed through the combination of structural, experimental, and theoretical investigations. Especially, the rates of quantum tunneling of magnetization of 1-4 were theoretically predicted and are consistent with the experimental results. For 2 and 4, the theoretically calculated dipolar parameters J_dip are consistent with the experimental observation of weak ferromagnetic coupling.

Structurally modulated single-ion magnets of mononuclear β-diketone dysprosium(iii) complexes

Four perturbed eight-coordinated mononuclear β-diketone based Dy(iii) SIMs with distinct hydrogen bond interactions and electron delocalization are noteworthily modulated by the aromatic groups of auxiliary ligands.

Switchable slow relaxation of magnetization in photochromic dysprosium(iii) complexes manipulated by a dithienylethene ligand

The admirable photochromic and magnetic properties of two dithienylethene-based complexes can be modulated with UV/Vis light irradiation.

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.

The stepwise substitution in the hierarchical building of {Co11Cd6} cluster-based MOFs from {Co14} precursor

A heterometallic aggregation of {Co₁₁Cd₆} can be hierarchical built from a {Co₁₄} precursor directly. HRESI-MS technique was used to track the stepwise Cd²⁺-capture: {Co₁₄} → {Co₈} → {Co₈Cd₂} → {Co₈Cd₃} → {Co₈Cd₄} → {Co₈Cd₅} → {Co₈Cd₆} → {Co₁₁Cd₆}.

Two Dy(III) Single-Molecule Magnets with Their Performance Tuned by Schiff Base Ligands

To develop new lanthanide single-molecule magnets (SMMs), two new complexes of [Dy₂(MeOH)₂(HL¹)₂(NO₃)₂]·2MeOH (1) and [Dy₆(μ₃-OH)₂(L²)₂(HL²)₂(H₂L²)₂Cl₂(EtOH)₂]Cl₂·3EtOH·CH₃CN (2) were obtained by reacting Dy(NO)₃·6H₂O with 3-amino-1,2-propanediol in the presence of 2-hydroxynaphthaldehyde for 1 and by reacting DyCl₃·6H₂O with 1,1-di(hydroxymethyl)ethylamine in the presence of 2-hydroxynaphthaldehyde for 2, respectively, in which the Schiff base ligands of 3-(((2-hydroxynaphthaen-1-yl)methylene)amino)-propane-1,2-diol (H₃L¹) and 2-(β-naphthalideneamino)-2-(hydroxylmethyl)-1-propanol (H₃L²) were in situ formed. The two Dy(III) ions in 1 are linked by two O_alkoxy atoms of two (HL¹)^2- ligands to build a dinuclear skeleton. Complex 2 presents a nearly planar hexanuclear skeleton constructed from four edge-shared triangular Dy₃ units with the two peripheral Dy₃ units consolidated by two μ₃-O bridges and the two central Dy₃ units consolidated by one μ₃-O bridge. Obviously, they exhibit a different topological arrangement resulting from the linkage of the Schiff base ligands. Both of them are typical SMMs under zero dc fields, with a U_eff/ k_B value of 34 K for 1 and 40 K for 2, respectively. Multiple processes are involved in the relaxation processes of 1 and 2. The different SMM performances of the two titled complexes reveal a tuning effect of Schiff base ligands through tuning the coordination environments and topological arrangements of dysprosium(III) ions, which is supported by the theoretical calculations.

Designing a mononuclear DyIII single-molecule magnet (SMM) by using a N,O,N,O-based multichelating Schiff base ligand and a β-diketonate ligand

Two mononuclear Ln^III compounds, in which each Ln^III is eight-coordinated, namely [Ln(L)(tmpd)] (Ln = Dy (1) or Er (2)), have been prepared using a multichelating Schiff base ligand (H₂L) and a bidentate chelating β-diketonate ligand (tmpd).

Two mononuclear dysprosium(iii) complexes with their slow magnetic relaxation behaviors tuned by coordination geometry

We report here two field-induced single-ion magnets of Dy(iii), which present octahedral and pentagonal–bipyramidal coordination geometries, respectively, with their magnetic performances tuned by the coordination geometries of Dy(iii).

Three Dy(iii) single-ion magnets bearing the tropolone ligand: structure, magnetic properties and theoretical elucidation

Three Dy(iii) SIMs bearing the tropolone ligand are reported here with the tuning effect on their performances by ancillary ligands revealed via experimental magnetic investigations and theoretical calculations.

Hemiporphyrazine-Involved Sandwich Dysprosium Double-Decker Single-Ion Magnets

Both heteroleptic (phthalocyaninato)(hemiporphyrazinato) and homoleptic bis(hemiporphyrazinato) dysprosium double-decker complexes, Dy[H(Hp)₂] (1) and Dy[H(Pc)(Hp)] (2) (H₂Pc = metal-free phthalocyanine; H₂Hp = metal-free hemiporphyrazine), were designed, synthesized, and structurally characterized. The dysprosium center in both double-deckers are octa-coordinated with a nearly ideal square-antiprismatic coordination geometry, which provides an increased molecular anisotropy for the dysprosium ion and ensures the strengthened magnetic properties of both single-ion magnets (SIMs) in terms of coordination geometry. Magnetic studies reveal that both double-deckers exhibit typical SIM behavior with a spin reversal energy barrier of 80.1 ± 6.3 K for 1 and 57.3 ± 3.8 K for 2 as well as the hysteresis loops emerging at 3 K. In particular, introduction of two Hp ligands with four pyridine nitrogen atoms coordinated with the dysprosium spin center endows Dy[H(Hp)₂] (1) with the thus far highest energy barrier among the sandwich-type dysprosium SIMs with N₄-macrocyclic ligands, revealing the potential applications of sandwich-type lanthanide complexes with Hp ligands in molecular-based information storage.

Lanthanide(III)-Based Single-Ion Magnets

Mononuclear lanthanide-based single-ion magnets (SIMs) are known since 2003 with the discovery of SIM properties in a bis-(phthalocyaninato)lanthanide complex. A recent report on [Dy(Cp^ttt)₂][BC₆F₅] indicating that it exhibits the highest known blocking temperature (60 K) has spurred fresh interest in this area. In this article, we discuss about the various requirements of lanthanide-based SIMs along with representative examples. Specifically, we describe the complexes whose coordination numbers vary from 2 to 8. We also discuss the representative examples of organometallic lanthanide complexes that can function as molecular magnets.

The slow magnetic relaxation regulated by the coordination, configuration and intermolecular dipolar field in two mononuclear DyIII single-molecule magnets (SMMs)

Tuning the magnetic dynamics of single-molecule magnets (SMMs) is a crucial challenge for chemists.

Experimental and theoretical interpretation of the magnetic behavior of two Dy(iii) single-ion magnets constructed through β-diketonate ligands with different substituent groups (–Cl/–OCH3)

Two Dy(iii) single-ion magnets, formulated as [Dy(Phen)(Cl-tcpb)₃] (Cl-1) and [Dy(Phen)(CH₃O-tmpd)₃] (CH₃O-2) were obtained through β-diketonate ligands (Cl-tcpb = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione and CH₃O-tmpd = 4,4,4-trifluoro-1-(4-methoxyphenyl)-1,3-butanedione) with different substituent groups (–Cl/–OCH₃) and auxiliary ligand, 1,10-phenanthroline (Phen). The Dy(iii) ions in Cl-1 and CH₃O-2 are eight-coordinate, with an approximately square antiprismatic (SAP, D_4d) and trigonal dodecahedron (D_2d) N₂O₆ coordination environment, respectively, in the first coordination sphere. Under zero direct-current (dc) field, magnetic investigations demonstrate that both Cl-1 and CH₃O-2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behavior with different effective barriers (U_eff) of 105.4 cm⁻¹ (151.1 K) for Cl-1 and 132.5 cm⁻¹ (190.7 K) for CH₃O-2, respectively. As noted, compound CH₃O-2 possesses a higher effective barrier than Cl-1. From ab initio calculations, the energies of the first excited state (KD₁) are indeed close to the experimental U_eff as 126.7 cm⁻¹vs. 105.4 cm⁻¹ for Cl-1 and 152.8 cm⁻¹vs. 132.5 cm⁻¹ for CH₃O-2. The order of the calculated energies of KD₁ is same as that of the experimental U_eff. The superior SIM properties of CH₃O-2 could have originated from the larger axial electrostatic potential (ESP_(ax)) felt by the central Dy(iii) ion when compared with Cl-1. The larger ESP_(ax) of CH₃O-2 arises from synergic effects of the more negative charge and shorter Dy–O distances of the axial O atoms of the first sphere. These charges and distances could be influenced by functional groups outside the first sphere, e.g., –Cl and –OCH₃.

Further studies from the viewpoint of electrostatic potential demonstrate that the larger axial electrostatic potential (ESP) felt by the central Dy (iii) ion of CH₃O-2 is responsible for its better SIM property when compared with Cl-1.