Search

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. [ABSTRACT FROM AUTHOR]

Terminal fluoride ligands generate strong magnetic anisotropy in air-stable chiral dysprosium enantiomers supported by a bulky equatorial macrocycle, exhibiting a typical zero-field single-molecule magnet behaviour. [ABSTRACT FROM AUTHOR]

A dinuclear complex with the formula Dy2L2(H2L)Cl2(EtOH)2 (Dy2) has been synthesized by reacting DyCl3·H2O with a ligand H2L (H2L = N,N′-ethylenebis(salicylideneimine)) using ethanol as the solvent. Its crystal structure can be viewed as a dimer of two Dy(III) fragments, where each Dy(III) site shows a N2O6Cl coordination sphere with a pentagonal bipyramid geometry (D5h). Magnetic measurements reveal that Dy2 behaves as a single-ion magnet (SIM) under a zero field. When the field is applied, the ac magnetic susceptibilities show double and triple peaks under high (≥600 Oe) and low (<600 Oe) dc fields, respectively. In contrast to the common double relaxation pathways in SIMs, such multiple and intricate relaxation pathways have not been reported yet in the previous literature. In this work, by experimental analysis of the ac signals, we attribute the three slow relaxation pathways to quantum tunnelling of magnetization (QTM), intermolecular dipole–dipole interaction and spin reversal, respectively. In addition, ab initio calculations are used to elucidate the magnetic behaviours of Dy2. Overall, our work indicates that the interpretation of the relaxation process using double relaxation pathways is incomplete and difficult in previously reported literature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three mononuclear, dinuclear and one-dimensional dysprosium(III) complexes based on 3-azotriazolyl-2,6-dihydroxybenzoic acid (H4ATB) of [Dy(H3ATB)3]·3H2O (1), [Dy2(H2ATB)2(H2DHB)2(H2O)4]·2CH3CN·5H2O (2), and [Dy2(H2ATB)2(DCB)(DMF)2(H2O)2]·4DMF (3) were synthesized and structurally characterized by X-ray single crystal diffraction (H3DHB = 2,6-dihydroxybenzoic acid, H2DCB = 1,4-dicarboxybenzene). Complex 1 was used as a precursor to synthesize complexes 2 and 3, and 2 was further used to synthesize 3. Complex 1 is a mononuclear complex, in which the Dy(III) ion is in a nine-coordinated structure surrounded by three tridentate chelate H3ATB− ligands. Complex 2 displays a dinuclear structure bridged by two μ2 carboxyl groups of two H2DHB− ligands and two μ1,1-O atoms from the phenolic hydroxyl groups of two H2ATB2− ligands. Complex 3 shows a one-dimensional structure formed by two bridging DCB2− ligands. The magnetic measurements were performed on three complexes 1–3, and they showed different magnetic behavior. Complex 1 shows a field-induced slow magnetic relaxation. Complexes 2 and 3 display distinct slow magnetic relaxation under zero dc field with energy barriers (Ueff) of 26(2) cm−1 and 11(1) cm−1, respectively. The magnetic behavior of three complexes 1–3 was investigated by ab initio calculations. [ABSTRACT FROM AUTHOR]

A dinuclear dysprosium cluster [Dy2(NO3)4(H2O)2(L)2]·2CH3CN was successfully prepared by employing HL (HL = 2,6-dimethoxyphenol) and Dy(NO3)3·6H2O in a mixture of CH3OH and CH3CN. The conversion of this Dy2 compound by reaction with additional deprotonated ligand generated a Dy9 cluster [Dy9(μ4-OH)2(μ3-OH)8(μ2-OCH3)4(NO3)8(H2O)8(L)4](OH)·2H2O with the well-known "diabolo" topology. Magnetic investigation revealed that both of the clusters exhibit typical SMM characteristics, and variable magnetic relaxation with the energy barrier changing from 217.87 K to 9.24 K along with the transition from a dinuclear dysprosium cluster to a nonanuclear one. Ab initio calculations further confirm the corresponding structure–activity relationships that originate the different magnetic behaviours. This design may afford a feasible strategy for modulating the magnetic relaxation dynamics of polynuclear systems. [ABSTRACT FROM AUTHOR]

A family of cyano-bridged 3d–4f 1D chain compounds, {RE[TM(CN)6(2-PNO)5]}·(H2O)4 {RE = YIII, TM = [FeIII]LS (1); RE = DyIII, TM = CoIII (3); RE = ErIII, TM = [FeIII]LS (4), CoIII (5); 2-PNO = 2-picoline-N-oxide} and {RE[TM(CN)6(2-PNO)5]} {RE = DyIII, TM = [FeIII]LS (2)}, were synthesized and characterized. Single-crystal X-ray diffraction studies reveal that compounds 1 and 3–5 are isostructural, while compound 2 has a similar 1D chain structure with a different chain to chain arrangement. An axially-elongated pentagonal bipyramidal (D5h) coordination geometry is formed with five 2-PNO ligands in the equatorial plane and two [TM(CN)6]3− on the apical sites around the rare earth ions in these compounds. A comparison of the magnetic relaxation behaviour in detail reveals that it is more favorable for the Er (4 and 5) than the Dy analogues (2 and 3) to exhibit SIM properties in this axially-elongated D5h coordination environment. Under zero dc field, ac susceptibility measurements show that the Dy analogues have no magnetic relaxation behaviour, while the Er analogues exhibit frequency dependence despite the strong QTM effect. Under a 1 kOe dc field, the Er analogues generally show 1–2 orders of magnitude longer relaxation time at each selected temperature and a higher relaxation energy barrier than the Dy analogues. And the RECo compounds (3 and 5) show a more suppressed QTM effect than the corresponding REFe (2 and 4) compounds, which may be ascribed to the elimination of the fluctuation field from the neighbouring [FeIII]LS ions. The ab initio calculations indicate the misplacement between the orientation of the main magnetic axis and the structural axis in the Dy analogues, and the relative consistency in the Er analogues, which should be the source of the Er analogues showing better SIM properties than the Dy analogues. [ABSTRACT FROM AUTHOR]

While assembling superparamagnetic units in a controlled manner is crucial for future applications of molecular nanomagnets, optimizing their magnetic properties while achieving directional assembly of these units still remains a formidable challenge. Herein, we demonstrate how the assembly of two dysprosium chain complexes, namely, [Dy2(L)2Cl2(CH3OH)3]n·nCH3OH (1) and [Dy(L)Cl(DMF)]n (2) (H2L = N'-(5-bromo-2-hydroxybenzylidene)pyrazine-N-oxide-carbohydrazide), can be successfully manipulated using an appropriate bridging ligand design. Both complexes contain similar dimeric units bridged by two alkoxido oxygens from an L2− ligand, but extended by its pyrazine-N-oxide group exhibiting two distinct coordination modes, namely, single and double pyrazine-N-oxide bridges, respectively. Magnetic studies reveal that both complexes display typical slow magnetic relaxation under zero direct-current field; however, the anisotropy barrier and the coercive field at 2 K for complex 2 are twice as much as that of 1. A further theoretical study indicates that switching the coordination mode from a single pyrazine-N-oxide bridge to double bridges can enhance both the magnetic anisotropy of dysprosium ions and magnetic coupling within the dimeric cores. The synergistic effect between the magnetic anisotropy of dysprosium ions and magnetic interactions among them directly contributes to the overall better performance of complex 2. [ABSTRACT FROM AUTHOR]

Based on the organic ligand 2,2′-(((pyridine-2,6-diylbis(methylene))bis((pyridin-2-ylmethyl)-azanediyl))-bis(methylene))diphenol (H2L), and dysprosium salts with different anions, two mononuclear and one dinuclear complexes, namely, [Dy(L)(H2O)](ClO4)·2CH3CH2OH (1), [Dy(L)(NO3)] (2) and [Dy2(L)(dbm)4] (3, Hdbm = dibenzoylmethane), were synthesized and structurally and magnetically characterized. In complexes 1 and 3, the Dy centers are octa-coordinated with triangular dodecahedral (local D2d symmetry) environments. Complex 1 is dimeric by hydrogen bond interactions between coordinated water molecules. In complex 3, two DyIII ions are linked by two phenoxy oxygen atoms to form a dinuclear cluster. The DyIII ion in complex 2 is nine-coordinated and adopts a spherical capped square antiprism geometry with a C4v symmetry. Magnetic measurements and theoretical calculations reveal that the magnetic couplings between two phenoxyl-bridging DyIII ions in complex 3 are antiferromagnetic and mostly originate from the exchange coupling. Both complexes 1 and 2 exhibit single molecule magnet behaviors under zero direct-current field with effective energy barriers of 50.94 K and 12.26 K, respectively. Complex 3 only exhibits frequency-/temperature-dependent out-of-phase signals, and no peak is observed. [ABSTRACT FROM AUTHOR]

The utilization of two Schiff-base ligands H2L1 and H2L2 (H2L1 = 4-chloro-2-(((3-ethoxy-2-hydroxybenzyl)imino)methyl) phenol, H2L2 = 2-(((3-ethoxy-2-hydroxybenzyl)imino)methyl)-4-methoxy-phenol) with different substituents at the backbone of phenol in the construction of dinuclear dysprosium single-molecule magnets (SMMs) is reported. Two complexes of formulae [Dy2(L1)2(NO3)2(EtOH)(DMF)]·2EtOH (1) and [Dy2(L2)2(NO3)2(MeOH)2] (2) have been prepared and structurally characterized. X-ray crystallographic analysis revealed that the four DyIII ions of 1 and 2 all adopt NO7 coordination environments. The two DyIII centers of 1 exhibit triangular dodecahedron (D2d) and square antiprism (D4d) geometries, respectively, while the two DyIII sites in 2 both show triangular dodecahedron geometry with D2d symmetry. Magnetic analyses indicated that both complexes display SMM behavior with energy barriers of 86.91 K (1) and 93.70 K (2), respectively. The slight enhancement of the energy barrier of 2 reveals that the coordination geometries of DyIII ions would affect the magnetic behaviors of 1 and 2. Complete Active Space Self-Consistent Field (CASSCF) calculations were conducted for 1 and 2 to illustrate the slight variation of the magnetic behaviors. The calculated results are well consistent with those of the experimental outcomes. [ABSTRACT FROM AUTHOR]

The photochromic and magnetic properties of two dithienylethene (DTE)-based complexes, [Dy(NO3)3(Lo)2(MeOH)] (1-o) and [Dy(NO3)3(Lo)3] (2-o) (Lo = 4,5-bis(2,5-dimethylthiophen-3-yl)-1,3-dimethyl-1,3-dihydro-2H-imidazol-2-one), were experimentally studied in detail with the help of theoretical calculations. Both complexes exhibit an instantaneous and strong reversible photochromic response to UV/Vis irradiation, as evidenced from spectroscopic tests, and complex 1-o behaves as a typical field-induced single-molecule magnet (SMM). By controlling the reaction ratio of Lo and Dy(NO)3, Lo replacing a coordinated methanol molecule in 1-o results in the production of complex 2-o, whose single-molecule behavior is off. Upon irradiation with 254 nm light, the SMM properties of 1-o deteriorate with the energy barrier decreasing from 68.1 to 44.3 K while the magnetic dynamics of complex 2-o shows no response to irradiation. Ab initio calculations reveal that the quantum tunnelling of magnetization between the ground Kramers doublets in 2-o is quite strong, leading to the disappearance of SMM behavior. For complex 1-o, the strong magnetic anisotropy and moderate quantum tunnelling of magnetization relative to 2-o give rise to an appropriate energy barrier for SMM. On the other hand, the decrease in energy barriers for 1-o after irradiation results from the weakening of magnetic anisotropy, which is caused by the stronger charge delocalization of the coordinated carbonyl oxygen atom of the ring-closed DTE ligand. By regulating the reactant ratio, two photochromic DTE-based Dy(III) complexes are obtained and the SMM properties of complex 1-o can be tuned by the light-induced isomerization of the dithienylethene ligand. [ABSTRACT FROM AUTHOR]

Five β-diketone based Dy(III) single-ion magnets (SIMs), [DyIII(TTA)3(AIP)]·0.5CH3CH2OH·0.5H2O (1), [DyIII(TTA)3(APIP)]·2CH3OH·H2O (2), [DyIII(TTA)3(DPP)] (3), [DyIII(TTA)3(BPP)]·0.5CH3CH2OH (4) and [DyIII(TTA)3(AIP)]·1.5H2O (5), were fully synthesized through alteration of their phenanthroline derivates (AIP = 2-(anthracen-9-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, APIP = 2-(4-(anthracen-9-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, DPP = 2,3-diphenylpyrazino[2,3-f][1,10]phenanthroline and BPP = 2,3-bis(2,5-dimethylthiophen-3-yl)pyrazino[2,3-f][1,10]phenanthroline). Magnetic investigations reveal that all the complexes perform as SIMs, with notably different effective barriers of 69.4 K (1), 147.3 K (2), 122.1 K (3) and 234.2 K (4) in zero direct current (dc) field. Complexes of 2 and 4 possess almost twofold higher effective barriers compared to 1 and 3. By analyzing the crystal structures, the distinct magnetic dynamics was found to stem from the variation in intermolecular hydrogen bond interactions and charge delocalization of auxiliary ligands. With the help of ab initio calculations, a change of auxiliary ligand brings about varying intensities of quantum tunnelling magnetization (QTM), which account for the distinguishable magnetic dynamics. With a combination of experimental and theoretical analyses, this work provides a visual and instructive perspective to the understanding of fine tuning auxiliary ligands to design structurally modulated SIMs of mononuclear β-diketone dysprosium(III) complexes. [ABSTRACT FROM AUTHOR]

We present the syntheses, crystal structures, magnetic properties and theoretical calculations performed on two dinuclear dysprosium complexes with formulas Dy2(L1)2(L2)2(CH3CH2OH)(CH3OH) (1) and Dy2(L1)2(L3)2(CH3OH)2·1.5CH3OH (2). Single-crystal X-ray structural data analyses showed that both complexes contain two nonequivalent dysprosium ions bridged by two phenolate oxygen atoms. In both complexes, each dysprosium site adopts a N2O6 coordination constitution and triangular dodecahedron (D2d) configuration geometry with different distortion degree. Both complexes display single-molecule magnet behavior manifested by frequency-dependent out-of-phase alternating current susceptibility signal peaks under a zero-applied dc field. The effective energy barrier of the magnetization reversal and relaxation time values are 61 K, 7.1 × 10−6 s (1) and 51 K, 1.9 × 10−6 s (2), respectively. Theoretical calculations revealed a drastic discrepancy between the orientations of the anisotropy axis of the Dy2 ion observed in these two dinuclear complexes, resulting from the different spatial arrangements of the mixed ligands in the core structure. [ABSTRACT FROM AUTHOR]

A class of cyano-bridged 3d–4f zig-zag chain compounds, {RE[TM(CN)6] (PNO)2(H2O)4}·(H2O) {RE = YIII, TM = [FeIII]LS (1); RE = DyIII, TM = [FeIII]LS (2), CoIII (3)}, have been synthesized and characterized by single-crystal X-ray diffraction. The rare earth ions in these compounds are situated in a slightly distorted triangular dodecahedral (D2d) coordination environment. The magnetic properties of compounds 1–3 have been comparatively studied in detail. Under a zero dc field, the temperature dependence of ac susceptibility measurements for YFe (1) indicates the absence of magnetic relaxation stemming from the single anisotropic [FeIII]LS ion. The dysprosium analogue DyFe (2) shows only magnetic relaxation behavior with a prominent QTM effect, while DyCo (3) exhibits SIM properties not completely covered by QTM, with an extracted energy barrier of 73 K under a zero dc field. The ab initio calculations indicate that both compounds 2 and 3 are SMMs with well-behaved magnetic relaxation properties primarily from the individual DyIII ion. Therefore, the different magnetic behaviors exhibited by compound 2 compared to 3 may be ascribed to the stronger QTM effect caused by the extra weak interaction of [FeIII]LS ions in 2 as a fluctuating transverse field around the DyIII ion. The QTM effect for both 2 and 3 is suppressed under an applied dc field with an effective energy barrier of 134 and 150 K, respectively. Compared with compound 2, the higher extracted Ueff/kB and χ′′(T) peak temperature for 3 should be further attributed to its slightly higher single-ion axiality as calculated and the elimination of the transverse field from the [FeIII]LS ion. [ABSTRACT FROM AUTHOR]

One-dimensional zig-zag chain and two-dimensional network dysprosium(III) single-molecule toroics with anisotropy barriers of about 5 and 31 cm−1 under a zero dc field are reported. These are the first one- and two- dimensional homometallic single-molecule toroics reported to date. Furthermore, the two complexes also display white-light emission under UV-light irradiation. [ABSTRACT FROM AUTHOR]

Two dysprosium complexes bearing unsupported Dy–Ge/Sn metal–metal bonds are reported here, wherein the Dy–Ge and Dy–Sn bonds both contain relatively large covalency. The complexes exhibit slow relaxation of magnetization at zero field with energy barriers of 485 and 620 K, respectively, and the blocking temperature of 6 K. [ABSTRACT FROM AUTHOR]

A unique belt-like one-dimensional Dy chain linked through hydroxyl groups was synthesized and structurally characterized. Magnetic studies showed that this Dy chain exhibited significant frequency-dependent ac behavior and clear hysteresis loop below 0.6 K. [ABSTRACT FROM AUTHOR]

Two novel dysprosium complexes, namely, [Dy2L2(NO3)2(DMF)2]·2DMF (1) and [Dy4L4(OAc)4(DMF)2] (2), have been successfully synthesized by reacting a new pyridine-N-oxide-containing organic ligand N′-(8-hydroxyquinoline-2-carboxaldehyde)pyridine-N-oxide-carbohydrazide (H2L) with different dysprosium salts. The single-crystal X-ray diffraction study revealed that they show either one-dimensional (1D) or tetranuclear structure that is governed by the coordination anion used during the reaction. Within the 1D structure of 1, the nine-coordinated Dy3+ ions are bridged by two phenol oxygen atoms from the 8-hydroxyquinoline group to form Dy2 dimers and these dimers are further connected by pyridine-N-oxide groups. While in 2, the two octa-coordinated Dy3+ ions are bonded together by both phenol oxygen and acetate bridges to produce the Dy2 units and two adjacent Dy2 units are further linked by pyridine-N-oxide groups, resulting in a tetranuclear structure. Magnetic studies indicate that the anisotropic Dy3+ ions in 1 and 2 are ferromagnetically and anti-ferromagnetically coupled, respectively. The alternating current (ac) susceptibility measurements revealed slow magnetic relaxation with effective energy barriers of Ueff = 18.0 K under zero dc field in complex 1. However, under zero dc field, the ac data for 2 show negligible out-of-phase signals, excluding the existence of slow magnetic relaxation. Theoretical studies indicate that the different magnetic relaxation behaviors of both complexes were attributed to the different coordination environments around Dy3+ ions and the distinct magnetic coupling between them. [ABSTRACT FROM AUTHOR]

In a field-induced single-ion magnet [(dtc)3Dy(phen)] (dtc− = diethyldithiocarbamate anion), replacing two of the S-based dtc− ligands with O-based dbm− ligands (dbm− = dibenzoylmethanoate anion) leads to a significant enhancement of magnetic anisotropy, yielding a rarely reported sulfur-ligated lanthanide-based single-ion magnet [(dbm)2Dy(dtc)(phen)]. Ab initio calculations reveal that the gz value of [(dbm)2Dy(dtc)(phen)] is much larger than that of [(dtc)3Dy(phen)], consistent with the experimental results. [ABSTRACT FROM AUTHOR]