Mononuclear Dysprosium Research Articles

Modification of slow relaxation of magnetization behavior via substituent change on two neutral mononuclear dysprosium(III) single-molecule magnets

Modification of slow relaxation of magnetization behavior via substituent change on two neutral mononuclear dysprosium(III) single-molecule magnets

Effect of variation of substitution groups attached on benzoxazole ligands on relaxation dynamics of a family of nona-coordinate mononuclear dysprosium zero-field single-molecule magnets

Taking advantage of modified substitution group strategy, the magneto-structural correlation of four nona-coordinate mononuclear dysprosium zero-field single-molecule magnets derived from benzoxazole ligands is established. Mixing of the corresponding benzoxazole ligands and dysprosium trifluoromethanesulfonate in the presence of methanol solvent yielded four nona-coordinate mononuclear dysprosium complexes 1–4 with the core molecular formula Dy(Lx-R)3 (R = F, 1, x = 1; CN, 2, x = 2; CF3, 3, x = 3 and C(CH3)3, 4, x = 4). The coordination geometries of the dysprosium metal site with N6O3 donor atoms in 1–4 are all belong to spherical capped square antiprism (C4v) and the detailed corresponding parameters are 1.509, 1.173, 1.412 and 1.377, respectively. The static and dynamic magnetic susceptibilities measurements were performed on 1–4. They all display frequencies-dependent ac out-of-phase component signal peaks at different temperatures and zero external field, characteristic of single-molecule magnets behaviour. Variable-field magnetization measurements performed at 2 K confirm the magnetization blocking for 1–4 and reveal the presence of butterfly shape magnetic hysteresis. The experimental resulted effective energy barriers for magnetization reversal for 1–4 are 48.6, 102.2, 113.5, and 120.6 K, respectively. To understand the origin of variation observed, we have performed ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations on complexes 1–4. The calculations reveal axial g-tensors within the ground KD state, aligning with experimental results, and contributing to the observed trend in barrier heights. The computed crystal field parameters show an increasing trend from 1 to 4, indicating strengthening axial bonds, while non-axial CF parameters decrease. Steric hindrance from bulky ligands correlates with weakened equatorial bond strength, further contributing to higher barrier heights. Additionally, the LoProp charge on axial atoms strengthens the bonds in the order 1 → 2 → 3 → 4, reaffirming the importance of strengthen axial bond and weakening equatorial bonds towards better performant SIMs. Our work demonstrates that ligand substituent group strategy applied on benzoxazoles can utilize to tune the magnetic anisotropy of nona-coordinate mononuclear dysprosium complexes.

Constructing high axiality mononuclear dysprosium molecular magnets via a regulation-of-co-ligands strategy.

Two lanthanide complexes with formulae [DyIII(LN5)(pentafluoro-PhO)3] (1) and [DyIII(LN5)(2,6-difluoro-PhO)2](BPh4) (2) (LN5 = 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadecal (19),2,13,15,17-pentaene) were structurally and magnetically characterized. DyIII ions lie in the cavity of a five coordinate nitrogen macrocycle, and in combination with the introduction of multi-fluorinated monodentate phenoxyl coligands a high axiality coordination symmetry is built. Using the pentafluorophenol co-ligand, complex 1 with a D2d coordination environment, is obtained and displays moderate single-molecule magnets (SMMs) behavior. When difluorophenol co-ligands were used, a higher local axisymmetric pentagonal bipyramidal coordination geometry was observed in complex 2, which displays apparent slow magnetic relaxation behavior with a hysteresis temperature of up to 5 K. Further magnetic studies of diluted samples combined with ab initio calculations indicate that the high axiality plays a crucial role in suppressing quantum tunneling of magnetization (QTM) and consequently results in good slow magnetic relaxation behavior. Different fluoro-substituted phenoxyl co-ligands have phenoloxy oxygen atoms with different electrostatic potentials as well as a different number of phenoloxy coligands along the magnetic axis, resulting in different ligand field strengths and coordination symmetries.

Understanding electrostatics and covalency effects in highly anisotropic organometallic sandwich dysprosium complexes [Dy(CmRm)2] (where R = H, SiH3, CH3 and m = 4 to 9): a computational perspective.

In this article, we have thoroughly studied the electronic structure and 4f-ligand covalency of six mononuclear dysprosium organometallic sandwich complexes [Dy(CmRm)2]n+/- (where R = H, SiH3, CH3; m = 4 to 9; n = 1, 3) using both the scalar relativistic density functional and complete active space self-consistent field (CASSCF) and N-electron valence perturbation theory (NEVPT2) method to shed light on the ligand field effects in fine-tuning the magnetic anisotropy of these complexes. Energy decomposition analysis (EDA) and ab initio-based ligand field theory AILFT calculations predict the sizable 4f-ligand covalency in all these complexes. The analysis of CASSCF/NEVPT2 computed spin-Hamiltonian (SH) parameters indicates the stabilization of mJ |±15/2〉 for [Dy(C4(SiH3)4)2]- (1), [Dy(C5(CH3)5)2]+ (2) and [Dy(C6H6)2]3+ (3) complexes with the Ucal value of 1867.5, 1621.5 and 1070.8 cm-1, respectively. On the other hand, we observed mJ |±9/2〉 as the ground state for [Dy(C7H7)2]3- (4) and [Dy(C8H8)2]- (5) complexes with significantly smaller Ucal values of 237.1 and 38.6 cm-1 respectively. For the nine-membered ring [Dy(C9H9)2]+ (6) complex, we observed the stabilization of the mJ |±1/2〉 ground state, with the first excited state being located ∼29 cm-1 higher in energy. AILFT-NEVPT2 ligand field splitting analysis indicates that the presence of π-type 4f-ligand interactions in complexes 1-3 help generate the axial-ligand field, while the δ-type interactions in complexes 4-5 generate the equatorial ligand field despite the ligands approaching from the axial direction. As the ring size increases, φ-type interactions dominate, generating a pure equatorial ligand field stabilising mJ |±1/2〉 as the ground state for 6. Calculations suggest that the nature of the ligand field mainly governs the Ucal values in the following order: 4f-Lσ > 4f-Lπ > 4f-Lδ > 4f-Lφ. Calculations were performed by replacing ligands with CHELPG charges to access the crystal field (CF) effects which suggests the stabilization of pure mJ |±15/2〉 in all the charge-embedded models (1Q-6Q). Our findings point out that the crystal field and ligand field effects complement each other and generate a giant barrier for magnetic relaxation in the small ring complexes 1-3, while a relatively weak crystal field and adverse 4f-Lδ/4f-Lφ interactions diminish the SMM behaviour in the large ring complexes 4-6.

Slow magnetic relaxation of a mononuclear dysprosium complex derived from 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione and 1,10-phenanthroline

A mononuclear dysprosium complex with a triangular dodecahedron geometry behaves as a single-molecule magnet with the effective barrier Ueff = 193 K.

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 D3h to Cs. 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.

A quasilinear hydrazone-based mononuclear dysprosium compound withC4vsymmetry exhibiting field-induced complex magnetic relaxation

AC4vsymmetrical mononuclear dysprosium(iii) compound has been successfully isolated using a new quasilinear single pyrazinyl hydrazone ligand. Single-ion behavior and the short-range intermolecular magnetic dipolar interaction are essential to the complex magnetic relaxation.

Eight coordinated mononuclear dysprosium complexes of heptadentate aminophenol ligands: the influence of the phenol substituents and the ancillary donors on the magnetic relaxation.

The mononuclear complexes [Dy(3Br,5Cl-H3L1,1,4)(D)]·solvate (D = H2O, solvate = 0.25MeOH, 1W·0.25MeOH; D = Py without solvate, 1Py), and [Dy(3NO2,5Br-H3L1,1,4)(H2O)] (2W) were isolated. The crystal structures of 1W·0.25MeOH, 1Py and 2W·2CH3C6H5 show that the DyIII ion is octacoordinated, in N4O4 or N5O3 environments, with distorted geometries, between square antiprism, biaugmented trigonal prism and triangular dodecahedral. A similar environment for the metal ion is shown in the chiral crystals of the diamagnetic yttrium analogue [Y(3Br,5Cl-H3L1,1,4)(MeOH)] (3M), which were spontaneously resolved. Magnetic analyses of the three dysprosium complexes, and their diluted analogous 1W@Y, 1Py@Y and 2W@Y, reveal that none of them seem to relax through an Orbach mechanism at Hdc = 0. However, the three complexes show Orbach relaxation under Hdc = 1000 Oe, and 1Py is the in-field SIM with the highest energy barrier among these complexes, with a Ueff value of 358 K. Analysis of ac magnetic data shows that the electron-withdrawing substituents on the phenol rings of the aminophenol ligands, as well as the auxiliary oxygen donors from water ligands, reduce the energy barriers of the complexes, which is attributed to a charge reduction in the coordinating atoms of the aminophenol donor. Ab initio calculations support the experimental results.

Structural Modulation of Fluorescent Rhodamine-Based Dysprosium(III) Single-Molecule Magnets.

Two rhodamine 6G-based mononuclear dysprosium complexes, [Dy(LR)(LA)2](ClO4)3·Et2O·1.5MeOH·0.5H2O (1) and [Dy(LR)(H2O)4(MeCN)](ClO4)3·2H2O·MeCN (2) (LR = salicylaldehyde rhodamine 6G hydrazone, LA = 2-pyridylcarboxaldehyde benzoyl hydrazone), are synthesized, aiming at improving the magnetic behavior by modulating their coordination environment. Both complexes own one exclusive short Dy-Ophenoxy coordination bond as the predominant bond and exhibit single-molecule magnet behavior under zero dc field with the energy barrier (Ueff/kB) of 90 K (1) and 320 K (2) and apparent hysteresis at 1.9 K. The ab initio calculations indicate that the short Dy-Ophenoxy bond determines the direction of magnetic anisotropic axis for 1 and 2. The quantum tunneling of magnetization (QTM) between the ground Kramers doublets (KDs) in 1 cannot be neglected, leading to an experimental Ueff/kB much lower than the calculated energy of the first excited state (318.2 K). For 2, the stronger magnetic anisotropy and negligible QTM between the ground KDs guarantees that the energy barrier is close to the calculated energy of first KDs (320.8 K). On the other hand, the presence of ring-opened xanthene moiety makes complexes 1 and 2 in the solid state emit red light with emission bands of 645 and 658 nm, respectively.

Investigation of magneto-structural relation based on a series of mononuclear dysprosium single-ion magnets with high Oh symmetry

Two mononuclear Dy(III) complexes [Dy(HL)2(CH3OH)Cl3] (1) and [Dy(L)2(CH3CH2OH)Cl3] (2) were obtained by organic ligand 5,7-dibromo-2-methyl-8-quinolinol (HL) with DyCl3·6H2O. Structure analysis suggested that the Dy(III) center in those two complexes had six octahedral coordinative configurations, but the symmetry of complex 2 (1.251) was obviously higher than that of complex 1 (1.419). The coordinated solvent molecule contributes significantly on the geometry of Dy(III) ions in the two diverse complexes. And magnetic investigations showed that complex 1 exhibited a weak field-induced single-molecule magnetic (SIM) behavior, but complex 2 showed obvious SIM behavior. For complex 2, the energy barriers were 36.8 (1) K and 50.8 (9) K, respectively. They are typical SMM examples with rare six coordination of Dy(III) ions.

Mononuclear dysprosium complex with single-ion magnetic behavior and its highly selective detection of 1,4-dioxane

The organic ligand 5,7-dibromo-2-methyl-8-quinolinol (L) was used to react with Dy(NO3)3·6H2O at 60 °C to obtain the complex [Dy(L)3(CH3CH2OH)(H2O)]·CH3CN (1). Furthermore, the electrospray mass spectrometry (ESI–MS) data show that the main molecular fragment was [DyL2(DMF)2]+ under the condition of 0 eV voltage. When complex 1 was dissolved in DMF and stayed for half a month, and it also showed the main molecular fragment after measuring ESI–MS. So complex 1 was relatively stable in DMF. And magnetic susceptibilities showed that 1 exhibits a clear field-induced SIM behavior, and the energy barriers and extrapolated relaxation time was Ueff = 14.6 K and τ0 = 4.1 × 10−5 s under 1000 Oe dc field. The complex 1 was dissolved in various organic solvents and tested for fluorescence. It was found to have very high selectivity in 1,4-dioxane and the fluorescence intensity was more than 3 times that of other organic solvents.

Bifunctional Mononuclear Dysprosium Complexes: Single-Ion Magnet Behaviors and Antitumor Activities.

Two mononuclear dysprosium complexes (Et3NH)[Dy(BrMQ)4]·H2O·DMF(BrMQ-Dy) and (Et3NH)[Dy(ClMQ)4]·H2O·DMF (ClMQ-Dy) (H-BrMQ = 5,7-dibromo-2-methyl-8-quinolinol, H-ClMQ = 5,7-dichloro-2-methyl-8-quinolinol) were synthesized and characterized. The Dy(III) ions in complexes BrMQ-Dy and ClMQ-Dy have a pseudo-D4d local symmetry. Magnetic characterizations reveal that complex BrMQ-Dy is a single-ion magnet and complex ClMQ-Dy exhibits field-induced slow magnetic relaxation behaviors. The calculated effective barriers of BrMQ-Dy, BrMQ-Dya, ClMQ-Dy, and ClMQ-Dya are 47.8, 27.3, 96.0, and 65.5 cm-1, respectively (BrMQ-Dya and ClMQ-Dya represent the desolvated samples of BrMQ-Dy and ClMQ-Dy, respectively). Ab initio calculations confirmed that coordination symmetry of the Dy(III) ions, electron-withdrawing ligands, and the guest molecules is a key factor affecting the magnetic dynamics of the two complexes. The IC50 values of BrMQ-Dy and ClMQ-Dy against BEL-7404, HeLa, and Hep-G2 cancer cells were 1.01-22.06 μM. Interestingly, two Dy(III) complexes were less toxic to normal HL-7702 cells. BrMQ-Dy and ClMQ-Dy significantly induced cell arrest at G2 phase and down-regulated the G2 phase-related protein levels. Various experiments suggested that BrMQ-Dy and ClMQ-Dy also caused dysfunction of mitochondrial pathways in HeLa cells. Taken together, the different in vitro anticancer activity of complexes BrMQ-Dy and ClMQ-Dy in the order of 5,7-dichloro substitution > 5,7-dibromo substitution.

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

Two mononuclear dysprosium(iii) complexes [Dy(H3NAP)2Cl2]Cl·EtOH (1) and [Dy(H3NAP)2(H2O)Cl2]Cl·-2CH3CN·MeOH·0.5H2O (2) were obtained by coordinating an in situ formed Schiff base ligand of 1,3-bis(2-hydroxynaphthalenemethyleneamino)-propan-2-ol (H3NAP) to the dysprosium(iii) ion. Their Dy(iii) centers are six and seven-coordinated in octahedral and pentagonal-bipyramidal coordination geometries, respectively. Their structural difference is caused by the additional coordinated water molecule in the equatorial positions of complex 2 in comparison with that of complex 1. The well designed semi-rigid ligand contributes significantly to the low coordination numbers of Dy(iii) ions in the two title complexes, as well as to their structural difference. Magnetic investigations revealed that complexes 1 and 2 are both field-induced single-ion magnets (SIMs) with their effective energy barriers being 22.9(6) and 153.9(5) K, respectively. They are typical SIM examples with their performances tuned by the coordination geometries of metal ions.

Effect of the Ligand Field Geometry on the Slow Magnetization Relaxation in Mononuclear Dysprosium Complexes

Effect of the Ligand Field Geometry on the Slow Magnetization Relaxation in Mononuclear Dysprosium Complexes

Fine-tuning of the molecular structures and magnetic anisotropy analysis of two mononuclear dysprosium–sulfur complexes

Two mononuclear sulfur-based dysprosium complexes [(dtc)3Dy(bipy)] (1Dy, dtc− = diethyldithiocarbamate anion, bipy = 2,2′-bipyridine) and [(dtc)3Dy(dmbipy)]·0.68CH3CN (2Dy, dmbipy = 4,4′-dimethyl-2,2′-bipyridine) were successfully synthesized and structurally characterized by X-ray diffraction. The DyIII centers of 1Dy and 2Dy are eight-coordinated by six S atoms from three dtc− ligands and two N atoms from bipy (1Dy) or dmbipy (2Dy). Magnetic measurements reveal that the magnetic properties of 2Dy are obviously better than those of 1Dy. Theoretical calculations based on the molecular crystal structures are performed to analyze the difference of the magnetic behavior in two complexes.

Mononuclear Dysprosium(III) Complexes with Triphenylphosphine Oxide Ligands: Controlling the Coordination Environment and Magnetic Anisotropy

We report the synthesis, structural and magnetic characterization of five mononuclear DyIII ion complexes using triphenylphosphine oxide as a monodentate ligand. They have formulae [DyIII(OPPh3)3(NO3)3] (1), [DyIII(OPPh3)4(NO3)2](NO3) (2), [DyIII(OPPh3)3Cl3] (3), [DyIII(OPPh3)4Cl2]Cl (4) and [DyIII(OPPh3)4Cl2](FeCl4) (5). These complexes are characterized using single crystal X-ray diffraction, which revealed that each complex has a unique coordination environment around the DyIII ion, which results in varying dynamic magnetic behavior. Ab initio calculations are performed to rationalize the observed magnetic behavior and to understand the effect that the ligand and coordination geometry around the DyIII ion has on the single-molecule magnet (SMM) behavior. In recent years, seven coordinate DyIII complexes possessing pseudo ~D5h symmetry are found to yield attractive blocking temperatures for the development of new SMM complexes. However, here we show that the strength of the donor ligand plays a critical role in determining the effective energy barrier and is not simply dependent on the geometry and the symmetry around the DyIII ion. Seven coordinate molecules possessing pseudo D5h symmetry with strong equatorial ligation and weak axial ligation are found to be inferior, exhibiting no SMM characteristics under zero-field conditions. Thus, this comprehensive study offers insight on improving the blocking temperature of mononuclear SMMs.

A new β-diketonate Dy(III) single‒ion magnet featuring multiple magnetic relaxation processes

A β-diketonate mononuclear dysprosium compound, [Dy(TFNB)3(bpy)] (1) (TFNB = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, bpy = 2,2′-bipyridine), has been prepared and structurally and magnetically characterized. X-ray crystallographic analysis reveals that 1 contains two crystallographically equivalent Dy(III) ions of which the eight-coordinate geometries uniformly behave as distorted square antiprismatic configurations (D4d). Magnetic investigations demonstrate that 1 displays dual relaxation processes of SMMs behavior with the effective barrier (ΔE/kB) of 23.44 K under 1200 Oe DC field, corresponding to the coexistence of two metal centers in the structure of the compound. The comparative studies of some Dy(III)-based SIMs with TFNB ligand have been conducted as well. Ab initio studies demonstrate that the Kramers doublet ground state is predominantly axial with the gz tensors of two Dy(III) fragments matching the Ising-limit factor (20) anticipated for the pure MJ = ±15/2 state.

Coupling photo-, mechano- and thermochromism and single-ion-magnetism of two mononuclear dysprosium-anthracene-phosphonate complexes.

DyIII(depma)3(NO3)3 (1) and DyIII(depma)4(NO3)2(CF3SO3) (2) differ structurally by the number of depma ligands and the supramolecular interactions (π-π and C-Hπ, respectively) between anthracene moieties. They exhibit single-ion-magnetism which is coupled to photo- and mechanochromism that are partially reversible by thermal annealing. The changes are associated with the formation and destruction of excimers.

Field-Induced Slow Magnetic Relaxation of Mono- and Dinuclear Dysprosium(III) Complexes Coordinated by a Chloranilate with Different Resonance Forms

We synthesized the dinuclear and mononuclear dysprosium(III) complexes [{Dy(Tp)2}2(Cl2An)]·2CH2Cl2 (1) and [Co(Cp)2][Dy(Tp)2(Cl2An)] (3), where Cl2An2− and Tp− are the chloranilate and hydrotris(pyrazolyl)borate ligand, respectively. In addition, the magnitude of the magnetic coupling between the lanthanide centers through the Cl2An2− bridge has been probed through the synthesis of [{Gd(Tp)2}2(Cl2An)]·2CH2Cl2 (2), which is a gadolinium(III) analogue of 1. Complexes 1–3 were characterized by infrared (IR) spectroscopy, elemental analysis, single-crystal X-ray diffraction, and SQUID measurements. IR and single-crystal X-ray structural analyses confirm that the coordination environments of the lanthanide(III) centers in 1 and 3 are similar to each other; i.e., eight-coordinated metal centers, each occupied by an N6O2 donor set from two Tp− ligands and one Cl2An2− ligand. The coordination geometries of the lanthanide(III) centers in 1 and 2 are distorted triangular dodecahedral, while that in the mononuclear complex 3 is square antiprismatic, where the Cl2An2− ligand takes the bi-separated delocalized form in 1 and 2, and the o-quinone form in 3. Alternating-current (AC) magnetic studies clearly reveal that both 1 and 3 exhibit field-induced slow relaxations of magnetization that occur via Raman and direct processes. Complexes 1 and 3 exhibit different spin relaxation behavior, which reflects the coordination geometry around each DyIII center and its nuclearity, as well as the molecular packing in the crystal lattice. Although the magnetic analysis of 2 revealed negligible magnetic coupling, Cl2An2− bridges with small biases may form in the dinuclear complexes, which play roles in the spin relaxation dynamics through dipolar interactions.

Single-molecule magnet behavior in a mononuclear dysprosium(iii) complex with 1-methylimidazole

Using 1-methylimidazole ligand and Dy(hfac)3·2H2O salt achieved a new single-molecule magnet of [Dy(hfac)3·(1-MeIm)2] with an energy barrier of 42.54 K.