Dy Single-molecule Magnets Research Articles

Making soluble Dy2 single-molecule magnets red emissive through their functionalization by ruthenium-cyanido luminophores.

We present an efficient strategy for obtaining red-emissive molecular nanomagnets by exploring a heterometallic approach. We report the {[DyIII(4-pyridone)5]2[RuII(CN)2(phen)2]2}·(CF3SO3)6·2MeOH (phen = 1,10-phenanthroline) compound composed of exchange-coupled {DyIII2} single-molecule magnets functionalized by Ru(II)-cyanido units. The latter makes the resulting {DyIII2RuII2}6+ cations a unique example of a soluble lanthanide SMM exhibiting red charge-transfer photoluminescence in the solution and solid state, well enhanced when compared with the cyanido precursor.

Homochiral Dy2 single-molecule magnets with strong magneto-optical Faraday effects and strong third-harmonic generation

Four pairs of enantiomers of ferromagnetically coupled Dy2 single-molecule magnets, which show both strong magneto-optical Faraday effects and strong third-harmonic generation, are directionally constructed.

From a Dy2 single-molecule magnet (SMM) to a 1D triangle-based Dy(III) chain SMM utilizing formate ions as bridging units

The reaction of Dy(NO3)2·6H2O with a Schiff base ligand N1,N3-bis(5-chlorosalicyladehyde)diethylenetriamine (H2bcsdt) afforded a dinuclear DyIII complex [Dy2(bcsdt)2(NO3)2] (1). The addition of HCOOH to the reaction system from which 1 was prepared generated a coordination polymer with the formula {[Dy3(bcsdt)3(HCOOH)(HCOO)(CO3)]·EtOH}n (2). Single-crystal X-ray diffraction analysis revealed that complex 2 possesses a one-dimensional chain structure based on a {[Dy3(bcsdt)3(HCOOH)(HCOO)(CO3)]·EtOH} repeating unit. In this unit, the three DyIII ions are connected by three oxygen atoms of one CO32– ion and display a nearly perfect triangle topology. The magnetic properties of 1 and 2 were investigated. They both exhibited slow relaxation of magnetization, indicative of single molecule magnet (SMM) behavior.

A nonsymmetric Dy2 single-molecule magnet with two relaxation processes triggered by an external magnetic field: a theoretical and integrated EPR study of the role of magnetic-site dilution.

The 1 : 2 reaction between Dy(O2CMe)3·4H2O and 1-acetyl-2-napthol (LH) in MeOH has provided access to the complex [Dy2L6(MeOH)]·MeOH (1·MeOH) in a good yield. The structures of the isomorphous complex 1·MeOH and its doped diamagnetic yttrium analogue [Dy0.14Y1.86L6(MeOH)]·MeOH (Dy@Y2) have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses, IR spectra, and powder X-ray patterns. Combined dc and ac magnetic susceptibility and the magnetization data for 1 suggest that this complex shows slow magnetic relaxation. Under a 0 Oe dc field, a single relaxation mechanism is seen while two magnetization relaxation processes are evident under a 1500 G external magnetic field. The fit to the Arrhenius law has been performed using the 1.8-10 K ac data, affording an effective barrier for the magnetization reversal of 13 K and 7 K under the external dc field. Theoretical studies have been performed using ab initio and density functional methodologies to understand the electronic structure and the magnetic relaxation dynamics resulting from the single DyIII ion as well as from the dinuclear exchange-coupled states. Rich powder EPR spectra at the X-band and Q-band were obtained from Dy@Y2, as well as from the 1·MeOH dimer, while simulation studies revealed the ferromagnetic nature of the interaction between the DyIII ions in accordance with theoretical studies.

Significantly Enhancing the Single-Molecule-Magnet Performance of a Dinuclear Dy(III) Complex by Utilizing an Asymmetric Auxiliary Organic Ligand.

In this work, we employed an asymmetric auxiliary organic ligand (1,1,1-trifluoroacetylacetone, Htfac) to further regulate the magnetic relaxation behavior of series of Dy2 single-molecule magnets (SMMs) with a N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2L) ligand. Fortunately, an air-stable Dy2 complex, [Dy2(L)2(tfac)2] (1; Htfac = 1,1,1-trifluoroacetylacetone) was obtained at room temperature. A structural analysis indicated that some Dy-O or Dy-N bond lengths for 1 are not in the range of those for the complexes [DyIII2(L)2(acac)2]·2CH2Cl2 (Dy2-acac; Hacac = acetylacetone) and [DyIII2(L)2(hfac)2] (Dy2-hfac; Hhfac = hexafluoroacetylacetone), although the electron-withdrawing ability of tfac- is stronger than that of acac- but weaker than that of hfac-. Additionally, the Dy-O3/O3a (the two O atoms bridged to DyIII ions) bond lengths are also affected by the asymmetrical Htfc ligand. This indicated that the charge distribution of the coordination atoms around DyIII has been modified in 1, which leads to the fine-tuning of the magnetic relaxation behavior of 1. Magnetic studies indicated that the values of effective energy barrier (Ueff) for 1 and its diluted sample (2) are 234.8(3) and 188.0(6) K, respectively, which are both higher than the reported value of 110 K for the complex Dy2-hfac. More interestingly, 1 exhibits a magnetic hysteresis opening when T < 2.5 K at zero field, while the hysteresis loops of 2 are closed at a zero dc field. This discrepancy is due to the weak intramolecular exchange coupling in 2, which cannot overcome the QTM of the single DyIII ion. Ab initio calculations for 1 revealed that the charge distributions of the coordination atoms around DyIII ions were regulated and the intramolecular exchange coupling was indeed improved when the asymmetrical Htfc was employed as a ligand for the synthesis of this kind of Dy2 SMM.

A Study of Magnetic Relaxation in Dysprosium(III) Single‐Molecule Magnets

Although the development of single-molecule magnets (SMMs) is rapid, there are only two families of high energy barrier (Ueff ) dysprosium(III) SMMs known so far: the cyclopentadienyl (Cp) family with a sandwich structure and the pentagonal-bipyramidal (PB) family with D5h symmetry. These high-barrier SMMs, which usually possess Ueff >500 cm-1 allow the separate study of the four magnetic relaxation paths, namely, direct, quantum tunnelling, Raman and Orbach processes, in detail. Whereas the first family is chemically more challenging to modify the Cp rings, it is shown herein that the latter family, with the common formulae [DyX1 X2 (Leq )5 ]+ , such as X1 /X2 =- OCMe3 , - OSiMe3 , - OPh, Cl- or Br- ; Leq =THF/pyridine/4-methylpyridine, can be readily fine-tuned with a range of axial and equatorial ligands by simple substitution reactions. This allows unambiguous confirmation that the Ueff mainly depends on the identity of X1 and X2 , rather than on Leq . More importantly, the fitted parameters are barrier dependent. If X1 is an O donor and X2 is a halide, 500<Ueff <600 cm-1 , log τ0avg (s)=-10.66, log Cavg (s-1 K-n )= -5.05, navg =4.1 and TH =9 K (in which τ0 is the pre-exponential factor for the Orbach relaxation process, C and n are parameters used to describe Raman relaxation, and TH is the highest temperature at which magnetic hysteresis is observed). For cases in which both X1 and X2 are O donors, 900<Ueff <1300 cm-1 , log τ0avg (s)=-11.63, log Cavg (s-1 K-n )= -6.03, navg =4.1 and 18<TH <25 K. Based on these results, it can be further concluded that Ueff not only has a linear correlation to the axial Dy-X bond lengths, but also to TH for these PB SMMs. This represents the first systematic study of a family of lanthanide SMMs and derives the first magneto-structural correlation in Dy SMMs.

Assembling two Dy2 single-molecule magnets with different energy barriers via fine-tuning the geometries of DyIII sites

Two Dy2 single-molecule magnets are prepared. The energy barrier of 2 is slightly enhanced by adjusting the geometries of DyIII centers.

An investigation into the magnetic interactions in a series of Dy2 single-molecule magnets.

Three di-nuclear DyIII complexes [Dy2(H2L)2(tfa)]·Cl·3DMF (1), [Dy2(H2L)2(MeO)(SCN)]·MeOH (2) and [Dy2(H2L)2(MeOH)Cl]·Cl·2MeOH (3) were synthesized and structurally and magnetically characterized. The Dy1/Dy2 centers in these complexes are all nine-coordinate with spherical capped square antiprism (local C4v symmetry) environments. All complexes display single-molecule magnet (SMM) behavior under zero applied dc field with their properties dependent on the nature of the magnetic interactions between the DyIII ions. Ab initio calculations substantiate that all DyIII ions show a weakly axial crystal-field environment with the exception of one of the DyIII ions in complex 2. The ground Kramers doublets show modest amounts of quantum tunneling of magnetization that gets blocked by the interaction between the DyIII ions, leading to a thermally activated slow relaxation of magnetization. The interaction between the ions is ferromagnetic and mostly originates from the dipolar interaction. However, anti-ferromagnetic intermolecular interaction plays an important role and in the case of complex 2 it is sufficiently strong to mask the ferromagnetic intramolecular interaction.

Enhancing single-molecule magnet behaviour through decorating terminal ligands in Dy2 compounds.

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric DyIII dimers, namely, [Dy2(bfbpen)2(H2O)2]·2I- (1) and [Dy2(bcbpen)2(H2O)2]·2I-·0.5H2O (2) (H2bfbpen = N,N'-bis-(2-hydroxy-5-fluoro-benzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine and H2bcbpen = N,N'-bis-(2-hydroxy-5-chloro-benzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy2 compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation.

Bromine-bridged Dy2 single-molecule magnet: magnetic anisotropy driven by cis/trans stereoisomers.

We report the first bromine-bridged dinuclear [Dy(Cy3PO)2(μ-Br)(Br)2]2·2C7H8 single-molecule magnet with an effective energy barrier of 684 K and magnetic hysteresis below 3 K. The asymmetric DyIII centres present two unique stereoisomeric octahedral coordination environments depending on the cis/trans disposition of the Cy3PO ligands, leading to the orthogonality of the easy magnetic axes that annihilates the dipolar interactions.

Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy2 Single-Molecule Magnets.

The utilization of 2-ethoxy-6-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol (H2 L) as a chelating ligand, in combination with the employment of alcohols (EtOH and MeOH) as auxiliary ligands, in 4 f-metal chemistry afforded two series of dinuclear lanthanide complexes of compositions [Ln2 L2 (NO3 )2 (EtOH)2 ] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7)) and [Ln2 L2 (NO3 )2 (MeOH)2 ] (Ln=Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Ho (13), Er (14)). The structures of 1-14 were determined by single-crystal X-ray crystallography. Complexes 1-7 are isomorphous. The two lanthanide(III) ions in 1-7 are doubly bridged by two deprotonated aminophenoxide oxygen atoms of two μ2 :η0 :η1 :η2 :η1 :η1 :η0 -L2- ligands. One nitrogen atom, two oxygen atoms of the NO3- anion, two methoxide oxygen atoms of two ligand sets, and one oxygen atom of the terminally coordinated EtOH molecule complete the distorted dodecahedron geometry of each lanthanide(III) ion. Compounds 8-14 are isomorphous and their structures are similar to those of 1-7. The slight difference between 1-7 and 8-14 stems from purposefully replacing the EtOH ligands in 1-7 with MeOH in 8-14. Direct-current magnetic susceptibility studies in the 2-300 K range reveal weak antiferromagnetic interactions for 3, 4, 7, 10, 11, and 14, and ferromagnetic interactions at low temperature for 5, 6, 12, and 13. Complexes 5 and 12 exhibit single-molecule magnet (SMM) behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12. The energy barrier is significantly enhanced by dexterously regulating the terminal ligands. To rationalize the observed difference in the magnetic behavior, complete-active-space self-consistent field (CASSCF) calculations were performed on two Dy2 complexes. Subtle variation in the angle between the magnetic axes and the vector connecting two dysprosium(III) ions results in a weaker influence on the tunneling gap of individual dysprosium(III) ions by the dipolar field in 12. This work proposes an efficient strategy for synthesizing Dy2 SMMs with high energy barriers.

Magnetic Relaxation Dynamics of a Centrosymmetric Dy2 Single-Molecule Magnet Triggered by Magnetic-Site Dilution and External Magnetic Field.

A centrosymmetric Dy2 single-molecule magnet (SMM) and its doped diamagnetic yttrium analogues, Dy0.19Y1.81 and Dy0.10Y1.90, were solvothermally synthesized to investigate the effects of intramolecular exchange coupling and quantum tunneling of magnetization (QTM) on the magnetic relaxation dynamics. Constructed from two hula-hoop-like DyIII ions and a pair of phenoxido groups, the antiferromagnetically coupled Dy2 exhibits a thermal-activated zero-field effective energy barrier (Ueff) of 277.7 K and negligible hysteresis loop at 2.0 K. The doping of a diamagnetic YIII matrix with 90.5% and 95.0% molar ratios reveals the single-ion origin of the Orbach channel, increases the relaxation time by partially quenching the QTM process, and induces an open hysteresis loop until 5.0 K. In contrast, an optimal dc field of 1.0 kOe improves the barrier height up to 290.1 K through complete elimination of the QTM and delays the relaxation time of the direct relaxation pathway. More interestingly, the collaborative dual effects of magnetic-site dilution and external magnetic field make the effective energy barrier and relaxation time increase 8.1% and 49 times, respectively. Thus, the overall magnetization dynamics of the Dy2 system systematically elaborate the inherent interplay of the QTM and Orbach processes on the effective energy barrier, highlighting the vital role of the relaxation time on the coercive hysteresis loop.

Complementation and joint contribution of appropriate intramolecular coupling and local ion symmetry to improve magnetic relaxation in a series of dinuclear Dy2 single-molecule magnets

The joint contribution of appropriate intramolecular coupling and local ion symmetry to improve magnetic relaxation in a series of dinuclear Dy2 SMMs.

Dysprosium Acetylacetonato Single-Molecule Magnet Encapsulated in Carbon Nanotubes.

Dy single-molecule magnets (SMMs), which have several potential uses in a variety of applications, such as quantum computing, were encapsulated in multi-walled carbon nanotubes (MWCNTs) by using a capillary method. Encapsulation was confirmed by using transmission electron microscopy (TEM). In alternating current magnetic measurements, the magnetic susceptibilities of the Dy acetylacetonato complexes showed clear frequency dependence even inside the MWCNTs, meaning that this hybrid can be used as magnetic materials in devices.

Site-Resolved Two-Step Relaxation Process in an Asymmetric Dy2 Single-Molecule Magnet.

Elaborate chemical design is of utmost importance in order to slow down the relaxation dynamics in single-molecule magnets (SMMs) and hence improve their potential applications. Much interest was devoted to the study of distinct relaxation processes related to the different crystal fields of crystallographically independent lanthanide ions. However, the assignment of the relaxation processes to specific metal sites remains a challenging task. To address this challenge, a new asymmetric Dy2 SMM displaying a well-separated two-step relaxation process with the anisotropic centers in fine-tuned local environments was elaborately designed. For the first time a one-to-one relationship between the metal sites and the relaxation processes was evidenced. This work sheds light on complex multiple relaxation and may direct the rational design of lanthanide SMMs with enhanced magnetic properties.

Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single-Molecule-Magnet Nodes within a Metal-Organic Framework.

Multitopic organic linkers can provide a means to organize metal cluster nodes in a regular three-dimensional array. Herein, we show that isonicotinic acid N-oxide (HINO) serves as the linker in the formation of a metal-organic framework featuring Dy2 single-molecule magnets as nodes. Importantly, guest solvent exchange induces a reversible single-crystal to single-crystal transformation between the phases Dy2(INO)4(NO3)2⋅2 solvent (solvent=DMF (Dy2-DMF), CH3CN (Dy2-CH3CN)), thereby switching the effective magnetic relaxation barrier (determined by ac magnetic susceptibility measurements) between a negligible value for Dy2-DMF and 76 cm(-1) for Dy2-CH3CN. Ab initio calculations indicate that this difference arises not from a significant change in the intrinsic relaxation barrier of the Dy2 nodes, but rather from a slowing of the relaxation rate of incoherent quantum tunneling of the magnetization by two orders of magnitude.

A Dy2 single-molecule magnet with benzoate anions and phenol-O(-) bridging groups.

A Dy2 single-molecule magnet, namely [Dy2(H3L)2(PhCOO)4]·4H2O (1), was obtained from the reaction of Dy(PhCOO)3 with 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide (H4L). Each Dy(III) ion is located in the chelating pocket [DyO8N] formed by the carboxyl-O, phenol-O, carbohydrazide-O and carbohydrazide-N, forming a tricapped trigonal prism configuration. The Dy(III) centers are bridged by the benzoate anions with μ2:η(1),η(2) coordination mode and the phenol-O(-) groups in the form of μ1:η(2), respectively. The appearance of frequency-dependent out-of-phase (χ''M) signals indicates that 1 displays single-molecule magnet (SMM) behaviour. Fits of the ac data gave an energy barrier (Ueff) of 42.7 K with a pre-exponential factor (τ0) of 1.31 × 10(-7) s. The structure-property relationship of some selected Dy2 paradigmatic compounds was further discussed.

An unsymmetrical coordination environment leading to two slow relaxation modes in a Dy2 single-molecule magnet

A Dy(2) single-molecule magnet was isolated using a mixed ligand strategy in which the Dy(III) ions adopt distinct coordination environments. This leads to two unique relaxation modes due to a single-ion type relaxation mechanism. Energy barriers were obtained from individually fitting the overlapping peaks.

Pyrazine-bridged Dy2 single-molecule magnet with a large anisotropic barrier

Utilization of the strong electron-withdrawing ligand, hfac, leads to a novel dinuclear dysprosium single-molecule magnet featuring a pyrazine bridge with a large anisotropic barrier.