English

• In recent years, a large number of Ln(Ⅲ)-based complexes have been synthesized and used in the study of single-molecule magnets (SMMs), including binuclear^[1], trinuclear^[2], tetranuclear^[3], pentanuclear^[4], hexanuclear^[5], heptanuclear^[6], and octanuclear^[7] Dy-(Ⅲ)-based complexes SMMs. Because the low nuclear complexes are easy to design and synthesize, the magnetic moment is easier to be an axial, and relatively large number of low nuclear Dy(Ⅲ)-based complexes showing SMMs behaviors have been reported^[8-10]. Binuclear Dy(Ⅲ)-based SMMs are an important model system, which can be used to answer whether the relaxation of the system comes from the relaxation of a single ion or the whole molecule^[11]. Therefore, a large number of binuclear Dy(Ⅲ)-based SMMs have been reported^[12-14]. In 2011, Tang group prepared an asymmetric Dy(Ⅲ) binuclear complex [Dy₂(ovph)₂Cl₂(MeOH)₃] ^[15]. Through experimental tests and theoretical calculations, it is found that there is a ferromagnetic coupling between Dy(Ⅲ) in this complex. Feng group^[16] reported a series of binuclear lanthanide complex, [Dy₂(Mq)₄(NO₃)₆] (Mq=2-methyl-8-hydroxyquinoline), which has exhibited SMM behavior. These binuclear Dy(Ⅲ)-based SMMs studies help to promote and stimulate the development of Ln(Ⅲ)-based single molecular magnetic materials and attract more inorganic chemists and materials scientists to design and construct Dy(Ⅲ)-based SMMs.

  Based on the above considerations, in this work, we try to find an efficient synthetic strategy for constructing two new Ln(Ⅲ)-based complexes showing remarkable magnetic behaviors. As shown in Scheme 1, a multidentate Schiff-base ligand H₂L (H₂L=(E)-N′-(3-ethoxy-2-hydroxybenzylidene)-3-hydroxypicolinohydrazide) with abundant coordination atoms and multiple coordination modes has been used to synthesize Ln(Ⅲ)-based binuclear complex. To further explore and study the relationship between the structure and magnetic properties of binuclear Ln(Ⅲ)-based complex, we designed and synthesized two new binuclear Ln(Ⅲ)-based complexes with the formula [Ln₂(dbm)₂(L)₂(C₂H₅OH)₂] (Ln=Dy (1), Nd (2); dbm^-=1, 3-dioxo-1, 3-diphenylpropan-2-ide) via the solvothermal method by using H₂L and Ln(dbm)₃·2H₂O. Structural analysis reveals that two central Ln(Ⅲ) ions are connected by two μ₂-O atoms forming a "parallelogram-shaped" Ln₂O₂ core. Magnetic analysis shows that the ferromagnetic interaction exists between the adjacent two Dy(Ⅲ) ions and 1 has SMM behavior.

  Scheme 1

  

  Scheme 1.  Structure of H₂L

  下载: 全尺寸图片 幻灯片

  1.   Experimental

  1.1   Materials and measurements

  1, 3-Diphenyl-1, 3-propanedione, 3-ethoxysalicylaldehyde, 3-hydroxy-2-picolinyl hydrazide, and Ln(NO₃)₃ ·6H₂O (Ln=Dy, Nd) were bought from Energy Chemical Co., Ltd., and the common solvents (ethanol, acetonitrile, and dichloromethane) were purchased from Komeo Reagent Co., Ltd. According to the previously reported method^[17], the multidentate Schiff base ligand H₂L was synthesized. Ln(dbm)₃ ·2H₂O was prepared according to the method reported in the literature^[18].

  Elemental analyses for complexes 1 and 2 were performed on a Perkin-Elmer 2400 analyzer. Infrared spectra data were measured with a Bruker TENOR 27 spectrophotometer. Powder X-ray diffraction (PXRD) data were collected using a Rigaku Ultima Ⅳ instrument with Cu Kα radiation (λ =0.154 056 nm) in a 2θ range from 5° to 50°. The operating voltage and current were 40 kV and 25 mA, respectively. Thermogravimetric analysis (TGA) data were recorded using a NETZSCHTG 409 PC thermal analyzer. The magnetic measurements were performed through a Quantum Design MPMS-XL7 and a PPMS-9 ACMS magnetometer.

  1.2   Preparations of H₂L and complexes 1 and 2

  1.2.1   Synthesis of H₂L

  To a suspension of 3-ethoxysalicylaldehyde (20.0 mmol, 3.32 g) in 10 mL methanol was added 3-hydroxy-2-picolinyl hydrazide (20.0 mmol, 3.08 g). The resulting reaction mixture was stirred at room temperature for 4 h. The white precipitate was collected by filtration and washed with methanol. The crude product was dried under vacuum for 48 h to give the ligand (H₂L) (Scheme 2). Yield: 3.99 g (63%). Elemental analysis Calcd. for C₁₆H₁₉N₃O₄(%): C, 60.50; H, 5.90; N, 13.23. Found(%): C, 60.55; H, 5.93; N, 13.24. IR (KBr, cm^-1): 3 291(m), 2 980(w), 2 929(w), 2 875(w), 2 834(w), 1 660 (s), 1 623(m), 1 577(m), 1 532(m), 1 451(s), 1 388(w), 1 330(w), 1 267(w), 1 246(s), 1 172(w), 1 089(w), 1 077 (m), 1 116(w), 1 010(w), 950(w), 967(m), 900(m), 833(m), 802(m), 783(m), 741(s).

  Scheme 2

  

  Scheme 2.  Synthesis of H₂L

  下载: 全尺寸图片 幻灯片

  1.2.2   Synthesis of complexes 1 and 2

  The synthesis method of complexes 1 and 2 was similar. Ln(dbm)₃·2H₂O (0.025 mmol, 0.021 g) was added to a solution of H₂L (0.025 mmol, 0.008 g) in 15 mL of CH₃OH/CH₂Cl₂/CH₃CN (3∶1∶1, V/V), and then the mixture was stirred for 30 min at room temperature. Whereafter, the mixture was sealed and packed in a glass sample vase (20 mL), which was heated at 80 ℃ for 24 h under autogenous pressure. Thereafter, it was cooled to room temperature, and yellow block crystals of 1 or 2 suitable for X-ray crystallography were obtained. The synthesis diagram of complexes 1 and 2 is shown in Scheme 3.

  Scheme 3

  

  Scheme 3.  Synthesis of complexes 1 and 2

  下载: 全尺寸图片 幻灯片

  [Dy₂(dbm)₂(L)₂(C₂H₅OH)₂] (1). Yield: 35% (based on Dy(dbm)₃·2H₂O). Elemental analysis Calcd. for C₆₄H₆₀Dy₂N₆O₁₄(%): C, 52.52; H, 4.10; N, 5.74. Found (%): C, 52.51; H, 4.09; N, 5.75. IR (KBr, cm^-1): 3 639 (w), 2 973(m), 2693(w), 1 594(s), 1 549(s), 1 515(m), 1 479(s), 1 444(s), 1 379(s), 1 334(m), 1 293(s), 1 250 (s), 1214(w), 1148(s), 1 113(w), 1 073(w), 1 036(w), 972(w), 935(w), 899(w), 850(m), 809(w), 746(m), 684 (m), 609(m), 552(w), 434(w).

  [Nd₂(dbm)₂(L)₂(C₂H₅OH)₂](2). Yield: 36% (based on Nd(dbm)₃·2H₂O).Elemental analysis Calcd. for C₆₄H₆₀Nd₂N₆O₁₄(%): C, 53.87; H, 4.20; N, 5.89. Found (%): C, 53.76; H, 4.19; N, 5.78. IR (KBr, cm^-1): 3 644 (w), 3 056(w), 2973(m), 2 693(w), 1 594(s), 1 549(s), 1 515(m), 1 479(s), 1 444(s), 1 379(s), 1 334(m), 1 293(s), 1 250(s), 1 214(w), 1 148(s), 1 113(w), 1 073(w), 1 036(w), 972(w), 935(w), 899(w), 850(m), 809(w), 746(m), 684(m), 609(m), 552(w), 462(w).

  1.3   X⁃ray crystallography

  Single crystal X-ray diffraction data of 1 and 2 were collected on a computer-controlled Rigaku Saturn CCD area detector diffractometer, equipped with confocal monochromatized Mo Kα radiation with a radiation wavelength of 0.071 073 nm, using the φ-ω scan technique. The structures of 1 and 2 were solved by direct methods and refined with a full-matrix least-squares technique based on F² using the SHELXTL programs. Anisotropic thermal parameters were assigned to all non-hydrogen atoms. Crystallographic data and structure refinement parameters of complexes 1 and 2 are listed in Table 1. Selected bond lengths and angles are given in Table S1 and S2 (Supporting information).

  Table 1

  

  Table 1.  Crystallographic data and structure refinements for complexes 1 and 2

  下载: 导出CSV

  Parameter	1	2
  Formula	C64H60Dy2N6O14	C64H60Nd2N6O14
  Formula weight	1 462.18	1 425.66
  T/K	150.0	150
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a/nm	1.303 26(4)	1.311 32(10)
  b/nm	1.421 83(4)	1.427 74(10)
  c/nm	1.880 84(5)	1.880 80(12)
  α/(°)	100.036 0(12)	99.822(4)
  β/(°)	102.275 7(12)	102.555(5)
  γ/(°)	114.247 9(12)	113.953(5)
  V/nm3	2.968 23(15)	3.005 9(4)
  Z	2	2
  Crystal size/mm	0.36×0.31×0.28	0.37×0.26×0.13
  Dc/(g·cm-3)	1.636	1.575
  μ/mm-1	2.570	13.619
  Limiting indices	-16 ≤ h ≤ 16, -17 ≤ k ≤ 17, -23 ≤ l ≤ 23	-16 ≤ h ≤ 16, -17 ≤ k ≤ 17, -23 ≤ l ≤ 17
  Reflection collected	74 997	37 740
  Unique reflection	12 159	12 168
  Parameter	787	787
  Rint	0.045 1	0.078 4
  GOF on F2	1.073	1.006
  R1, wR2 [I > 2σ(I)]	0.026 4, 0.068 6	0.054 4, 0.140 8
  R1, wR2 (all data)	0.036 5, 0.073 3	0.068 0, 0.154 8

  CCDC: 2100188, 1; 2133336, 2.

  2.   Results and discussion

  2.1   Crystal structures of 1 and 2

  Single-crystal X-ray diffraction analysis revealed that complexes 1 and 2 are isostructural and crystallize in the triclinic space group P1 with Z=2. Therefore, only the structure of 1 is described here in detail as a representative. As depicted in Fig. 1, complex 1 contains two Dy(Ⅲ) ions, two L^2- ions, two coordinated C₂H₅OH molecules, and two dbm^- ions. Each Dy(Ⅲ) ion center is eight-coordinated (Fig. 2), the central Dy1 ion is coordinated by two nitrogen atoms (N4 and N6) and six oxygen atoms (O14, O9, O12, O13, O10, and O10a) from two L^2- ions, a C₂H₅OH molecule and two dbm^- ions. The eight-coordinated center Dy(Ⅲ) ion shows a triangular dodecahedron. These geometrical configurations were confirmed by using the SHAPE 2.0 software (Table S3). The coordination modes of L^2- and dbm^- are shown in Fig. 3. L^2- packages two central Dy(Ⅲ) ions by the mode of multidentate chelation, and dbm^- connects each central Dy(Ⅲ) ions by the mode of bidentate chelation. Two central Dy(Ⅲ) ions are bridged by two μ₂-O atoms (O10 and O10a) of two L^2- ligands forming a parallelogram Dy₂O₂ core. In the Dy₂O₂ core, the distance of Dy1…Dy1a is 0.397 44(5) nm, the angles of Dy1— O10—Dy1a and O10—Dy1—O10a are 114.101° and 65.899°, respectively. Moreover, in complex 1, the bond distances of Dy—O are in a range of 0.217 2(2)-0.244 4(3) nm, and the Dy—N bond lengths are in a range of 0.248 5(3)-0.254 5(3) nm, respectively. The O—Dy—O bond angles are in a range of 65.61(9)°-148.30(9)°, which are comparable to those of the reported binuclear Dy(Ⅲ)-based complexes^[19-20].

  Figure 1

  

  Figure 1.  Molecular structure of 1 shown with 30% probability displacement ellipsoids

  All hydrogen atoms are omitted for clarity; Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片

  Figure 2

  

  Figure 2.  (a) Coordination environment of Dy₂; (b) Geometric polyhedron of Dy₂ ions observed in complex 1

  Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片

  Figure 3

  

  Figure 3.  Coordination modes for L^2- and dbm^-

  Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片

  2.2   PXRD and TGA for the complexes

  The purity of the crystal samples was checked by using PXRD. As shown in Fig. S2, the experimental PXRD patterns of 1 and 2 were almost identical to the corresponding simulated ones, which suggests that the purities of crystal samples 1 and 2 are high.

  The thermal stability of complexes 1 and 2 was studied using the crystalline samples under an air atmosphere from 25 to 800 ℃. The TGA curves of complexes 1 and 2 are shown in Fig.S3, and they exhibited similar thermal behaviors because they are isostructural. Herein, complex 1 is selected as a representative illustration. Between 40 and 223 ℃, a weight loss of 6.17% took place, which corresponds to the loss of two coordinated ethanol molecules (Calcd. 6.29%). Subsequently, a weight loss of 66.16% was observed from 223 to about 650 ℃, which is related to the loss of another twenty-one coordinated ethanol molecules (Calcd. 69.21%). Thereafter, complex 1 decomposed gradually in a temperature range of 450-800 ℃.

  2.3   Magnetic properties

  Under an external field of 1 000 Oe, the static direct (dc) magnetic susceptibility study of complex 1 was performed in a temperature range of 2.0-300.0 K. As shown in Fig. 4, the room-temperature χ_MT value of complex 1 was 28.75 cm³·K·mol^-1. This is in good agreement with the expected values for two isolated Dy(Ⅲ) ions (⁶H_15/2, g=4/3) of 28.34 cm³·K·mol^-1 for 1. When the temperature decreased, the χ_MT value of complex 1 decreased slowly in a range of 300.0-20.0 K. Then, the χ_MT value of complex 1 increased rapidly at 2.0 K, reaching the maximum value of 30.85 cm³·K· mol^-1. This indicates the possible existence of ferromagnetic coupling between the adjacent Dy(Ⅲ) ions in 1^[21].

  Figure 4

  

  Figure 4.  Temperature dependence of χ_MT at 1 000 Oe for complex 1

  下载: 全尺寸图片 幻灯片

  For complex 1, due to both factors of spin-orbit coupling and electronic interaction, the 4fⁿ electronic configuration of Dy(Ⅲ) ions can be split into ^2s+1L_J spectral branches. Affected by the crystal field perturbation, each ^2s+1L_J spectral term will be further split into multiple Stark sublevels, and these Stark sublevels are thermally populated. The population at these sublevels decreases with decreasing temperature, resulting in a decrease in the dc temperature-dependent magnetic susceptibility values of Dy(Ⅲ) with decreasing temperature. The χ_MT vs T curve of complex 1 increased with decreasing temperature, indicating a ferromagnetic interaction between the Dy(Ⅲ) ions, which counteracts or surmounts the decreasing trend of the χ_MT value caused by the thermal depopulation of the Dy(Ⅲ) Stark sublevels, and occupies a dominant position at low temperature^[22-23].

  To investigate the slow magnetic relaxation behavior of complex 1, alternating-current (ac) magnetic susceptibility was measured at 3.0 Oe ac field under a zero dc field and in a frequency range of 111-2 311 Hz (Fig. S4). Complex 1 exhibited remarkable frequency-dependent out-of-phase (χ″) signals and more than two peaks are observed in both in-phase (χ′) and χ″. This indicates multiple magnetic relaxation behavior, typical of SMM behavior in 1. To check the quantum tunneling of magnetization (QTM) effect above 2.0 K in 1, the variable-temperature ac susceptibilities were determined under an extra dc field of 5 000 Oe (Fig. 5). In the out-of-phase, remarkable shoulder peaks were observed in the frequency region (10-999 Hz) and temperature region (4.0-10.0 K), and the rising tail of χ″ at the low-temperature region was not observed. It proves that the quantum tunneling effect in complex 1 is pronounced and the QTM effect is suppressed under an external 5 000 Oe dc field. As shown in Fig. 6, we analyzed the frequency-dependent relaxation time and fitted the ln τ vs T^-1 plot of 1 by using the Arrhenius law^[24]: τ= τ₀exp[Δ E/(k_BT)]. The energy barrier (ΔE/k_B) of 56.77 K and the pre-exponential factor (τ₀) of 1.10×10^-7 s were obtained. The τ₀ of complex 1 was in the normal range of some reported values of 10^-6-10^-12 s for SMMs^[25-28]. The ΔE/k_B value of 1 was higher than some of the reported dinuclear dysprosium complexes^[29-36] (Table 2).

  Figure 5

  

  Figure 5.  Temperature-dependence of χ′ and χ″ components of the ac magnetic susceptibility for 1 under 5 000 Oe dc field with an oscillation of 3.0 Oe

  下载: 全尺寸图片 幻灯片

  Figure 6

  

  Figure 6.  Plot of ln τ vs T^-1 fitting to the Arrhenius law for complex 1

  下载: 全尺寸图片 幻灯片

  Table 2

  

  Table 2.  Comparison of energy barrier (ΔE/k_B) of recently reported Dy₂ SMMs and complex 1 in this work

  下载: 导出CSV

  Dy2-SMM	ΔE/kB/K	Reference
  [Dy2(hfac)4(L)2]	6.77	[29]
  [Dy2(L1)2(hfac)6]·C7H16	6.81	[30]
  [Dy2(tmhd)2L2(CH3OH)2]	13.14	[31]
  {[Dy2(bpda)3(H2O)3]4·2H2O}	1.14	[32]
  [Dy(bfa)2L]2	24.3	[33]
  [Dy2(dbm)4L·CH3OH]	28	[34]
  [Dy2(L2)2]	33	[35]
  Dy2(L1)2(L2)2(CH3CH2OH)(CH3OH)	61	[36]
  [Dy2(dbm)2(L)2(C2H5OH)2]	56.77	This work

  For further probing and studying the SMM behavior of 1, in the temperature range of 2.0-14.0 K, the frequency dependence (0-10 000 Hz) of χ′ and χ″ magnetic ac susceptibility was measured under an external field of H_dc=0 Oe (Fig. 7). The χ″ vs ν plot of 1 showed evident peaks, indicating that SMM behavior exists in 1^[37-40].

  Figure 7

  

  Figure 7.  Frequency dependence of χ′ and χ″ for 1 at 2.0-14.0 K under a zero dc field

  下载: 全尺寸图片 幻灯片

  From the frequency dependence of χ″, we obtained the ln τ vs T^-1 curve (Fig.S5). It is noteworthy that the plot of ln τ vs T^-1 showed an obvious curvature, which indicates that perhaps another relaxation pathway is also operative. In view of this, we fitted the ln τ vs T^-1 plot by using the equation^[41]: ln τ =-ln{AT+B+CTⁿ+τ₀^-1exp[ΔE/(k_BT)]}, where AT+B, CTⁿ, and τ₀^-1exp[ΔE/(k_BT)] represent direct, Raman and Orbach relaxation processes, respectively. The best-fitting was obtained for ΔE/k_B=55.08 K, τ₀=1.73×10^-7 s, n=4.9, A= 0.387 6 s^-1 ·K^-4.9, and C=0.065 43. The small A and C parameters indicate that the relaxation process can dominate by the Orbach mechanism at high temperatures and the Raman mechanism at low temperatures where the curvature of the Arrhenius plot is the transition from Raman to Orbach relaxation.

  The Cole-Cole plots of complex 1 are shown in Fig. 8. The Debye model was used to fit the Cole-Cole curves in a temperature range of 2.0 to 14.0 K, and the obtained α values were in a range of 0.17-0.65. However, some curves were not well fitted because there wasn′t only one semicircle at these temperatures (T=4.0-9.0 K), and good results were also not obtained for double magnetic relaxation fitting. The large α value indicates that there is a wide magnetic relaxation distribution in complex 1, and there may be multiple magnetic relaxation processes in 1.

  Figure 8

  

  Figure 8.  Cole-Cole plots for 1 measured under a zero dc field

  Red solid lines are the best fitting to the experimental data, obtained with the generalized Debye model with α=0.17-0.65 for 1

  下载: 全尺寸图片 幻灯片

  3.   Conclusions

  In summary, we have designed and synthesized two new binuclear Ln(Ⅲ)-based complexes by using a flexible polydentate Schiff base ligand (H₂L) and Ln(dbm)₃·2H₂O (Ln=Dy, Nd). The structures analysis reveals that the two central Ln ions are connected by two μ₂-O atoms forming a "parallelogram-shaped" Ln₂O₂ core. Magnetic studies show that the ferromagnetic interaction exists between the adjacent two Dy(Ⅲ) ions and the Dy₂ complex has single-molecule magnet behavior. As part of our research interests, the continued study of other Ln(Ⅲ)-based complexes is currently in progress for exploring outstanding properties.

  Supporting information is available at http://www.wjhxxb.cn

  
  
• 1. [1]

     Tuna F, Smith C A, Bodensteiner M, Ungur L, Chibotaru L F, Mclnnes E L, Winpenny E P. A High Anisotropy Barrier in a Sulfur-Bridged Organodysprosium Single-Molecule Magnet[J]. Angew. Chem. Int. Ed., 2012, 51(28):  6976-6980. doi: 10.1002/anie.201202497

  2. [2]

     Tang J K, Hewitt I, Madhu N T, Chastanet G, Wernsdorfer W, Anson C E, Benenlli C, Sessoli R, Powell A K. Dysprosium Triangles Showing Single-Molecule Magnet Behavior of Thermally Excited Spin States[J]. Angew. Chem. Int. Ed., 2006, 45(11):  1729-1733. doi: 10.1002/anie.200503564

  3. [3]

     Lin P H, Burchell T J, Ungur L, Chibotaru L F, Wernsdorfer W, Murugesu M. A Polynuclear Lanthanide Single-Molecule Magnet with a Record Anisotropic Barrier[J]. Angew. Chem. Int. Ed., 2009, 48(50):  9489-9492. doi: 10.1002/anie.200903199

  4. [4]

     Gamer M T, Lan Y, Roesky P W, Powell A K, Clérac R. Pentanuclear Dysprosium Hydroxy Cluster Showing Single-Molecule-Magnet Behavior[J]. Inorg. Chem., 2008, 47(15):  6581-6583. doi: 10.1021/ic8008255

  5. [5]

     Langley S K, Moubaraki B, Murray K S. Magnetic Properties of Hexanuclear Lanthanide(Ⅲ) Clusters Incorporating a Central μ₆-Carbonate Ligand Derived from Atmospheric CO₂ Fixation[J]. Inorg. Chem., 2012, 51(7):  3947-3949. doi: 10.1021/ic3002724

  6. [6]

     Constantinos J M, Angelos B C, George K T, Aggelos P, Apostolos S. Heptanuclear Lanthanide [Ln₇] Clusters: From Blue-Emitting Solution-Stable Complexes to Hybrid Cluster[J]. Dalton Trans., 2014, 43(33):  12486-12494. doi: 10.1039/C4DT00701H

  7. [7]

     Tian H Q, Zhao L, Guo Y N, Tang J K, Liu Z L. Quadruple-CO₃^2- Bridged Octanuclear Dysprosium(Ⅲ) Compound Showing Single-Molecule Magnet Behaviour[J]. Chem. Commun., 2012, 48(5):  708-710. doi: 10.1039/C1CC15814G

  8. [8]

     Wang W M, Liu L, Cai C Z, Wu R F, Zhang Y Q, Li C G, Zhang Y P, Wang J J. Magnetic Refrigeration and Single-Molecule Magnet Behavior of Two Rhombus-Shaped Ln(Ⅲ)₄ (Ln = Gd, Dy) Clusters[J]. Polyhedron, 2019, 158:  365-370. doi: 10.1016/j.poly.2018.11.006

  9. [9]

     Wang W M, Hua Y P, Wu W L, Xu C Y, Qiao X Y, Tan Y, Liu S S, Hou W Y, Cui Y Y. Modulating Single-Molecule Magnet Behaviors of Dy₄^Ⅲ Clusters through Utilizing Two Different β-Diketonate Coligands[J]. Polyhedron, 2019, 160:  272-278. doi: 10.1016/j.poly.2018.12.046

  10. [10]

      Zhao X J, Dong H M, Li H Y, Zhang Y Q, Yang E C. Magnetic Relaxation Dynamics of a Centrosymmetric Dy₂ Single-Molecule Magnet Triggered by Magnetic-Site Dilution and External Magnetic Field[J]. Inorg. Chem., 2017, 56:  5611-5622. doi: 10.1021/acs.inorgchem.6b03089

  11. [11]

      Wang W M, Zhao B, Cui J Z, Zhang H X, Wang S Y, Shen H Y, Gao H L. Ligand Field Affected Single-Molecule Magnet Behavior of Lanthanide(Ⅲ) Dinuclear Complexes with an 8-Hydroxyquinoline Schiff Base Derivative as Bridging Ligand[J]. Inorg. Chem., 2015, 54:  10610-10622. doi: 10.1021/acs.inorgchem.5b01404

  12. [12]

      Liu C M, Sun R, Wang B W, Wu F, Hao X, Shen Z. Homochiral Ferromagnetic Coupling Dy₂ Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature[J]. Inorg. Chem., 2021, 60:  12039-12048. doi: 10.1021/acs.inorgchem.1c01218

  13. [13]

      Tang J K, Guo Y N, Chen X H, Xue S F. Modulating Magnetic Dynamics of Three Dy₂ Complexes through Keto-Enol Tautomerism of the o-Vanillin Picolinoylhydrazone Ligand[J]. Inorg. Chem., 2011, 50:  9705-9713. doi: 10.1021/ic2014978

  14. [14]

      Wang Y L, Han C B, Zhang Y Q, Liu Q Y, Liu C M, Yin S G. Fine-Tuning Ligand to Modulate the Magnetic Anisotropy in a Carboxylate-Bridged Dy₂ Single-Molecule Magnet System[J]. Inorg. Chem., 2016, 55:  5578-5584. doi: 10.1021/acs.inorgchem.6b00653

  15. [15]

      Guo Y N, Xu G F, Wernsdorfer W, Ungur L, Guo Y, Tang J K, Zhang H J, Chibotaru L F, Powell A K. Strong Axiality and Ising Exchange Interaction Suppress Zero-Field Tunneling of Magnetization of an Asymmetric Dy₂ Single-Molecule Magnet[J]. J. Am. Chem. Soc., 2011, 133(31):  11948-11951. doi: 10.1021/ja205035g

  16. [16]

      Feng S H, Yang F, Zhou Q, Zeng G, Li G H, Gao L, Shi Z. Anion Effects on the Structures and Magnetic Properties of Binuclear Lanthanide Single-Molecule Magnets[J]. Dalton Trans., 2014, 43(3):  1238-1245. doi: 10.1039/C3DT52634H

  17. [17]

      Xue S F, Zhao L, Guo Y N, Zhang P, Tang J K. The Use of a Versatile o-Vanilloyl Hydrazone Ligand to Prepare SMM-like Dy₃ Molecular Cluster Pair[J]. Chem. Commun., 2012, 48(71):  8946-8948. doi: 10.1039/c2cc34737g

  18. [18]

      Katagiri S, Tsukahara Y, Hasegawa Y, Wada Y. Energy-Transfer Mechanism in Photoluminescent Terbium(Ⅲ) Complexes Causing Their Temperature-Dependence[J]. Bull. Chem. Soc. Jpn., 2007, 80(8):  1492-1503. doi: 10.1246/bcsj.80.1492

  19. [19]

      Wang W M, Hu X Y, Yang Y, Zhao Y X, Kang X M, Wu Z L. Modulation of Magnetic Relaxation Behaviors via Replacing Coordinated Solvents in a Series of Linear Tetranuclear Dy₄ Complexes[J]. New J. Chem., 2020, 44(20):  8494-8502. doi: 10.1039/D0NJ01830A

  20. [20]

      Wang W M, Wu Z L, Zang Y X, Wei H Y, Gao H L, Cui J Z. Self-Assembly of Tetra-nuclear Lanthanide Clusters via Atmospheric CO₂ Fixation: Interesting Solvent-Induced Structures and Magnetic Relaxation Conversions[J]. Inorg. Chem. Front., 2018, 5(9):  2346-2354. doi: 10.1039/C8QI00573G

  21. [21]

      Li X L, Han L, Chen D M, Wang C, Wu J F, Tang J K, Shi W, Cheng P. Planar Dy₃+Dy₃ Clusters: Design, Structure and Axial Ligand Perturbed Magnetic Dynamics[J]. Dalton Trans., 2015, 44(47):  20316-20320. doi: 10.1039/C5DT03931B

  22. [22]

      Fang M, Zhao B, Zuo Y, Chen J, Shi W, Liang J, Cheng P. Unique Two-Fold Interpenetration of 3D Microporous 3d-4f Heterometal-Organic Frameworks (HMOF) Based on a Rigid Ligand[J]. Dalton Trans., 2009, (37):  7765-7770. doi: 10.1039/b903737c

  23. [23]

      Wang Y, Li X L, Wang T W, Song Y, You X Y. Slow Relaxation Processes and Single-Ion Magnetic Behaviors in Dysprosium-Containing Complexes[J]. Inorg. Chem., 2009, 49(3):  969-976.

  24. [24]

      Hu P, Zhu M, Mei X L, Tian H X, Ma Y, Li L C, Liao D Z. Single-Molecule Magnets Based on Rare Earth Complexes with Chelating Benzimidazole-Substituted Nitronyl Nitroxide Radicals[J]. Dalton Trans., 2012, 41(48):  14651-14656. doi: 10.1039/c2dt31806g

  25. [25]

      Chen Z, Fang M, Kang X M, Hou Y L, Zhao B. Assembly of Single Molecular Magnets from Dinuclear to 2D Dy-Compounds with Significant Change of Relaxation Energy Barriers[J]. Dalton Trans., 2016, 45(1):  85-88. doi: 10.1039/C5DT02444G

  26. [26]

      Ren Y X, Zheng X J, Li L C, Yuan D Q, An M, Jin L P. Three-Dimensional Frameworks Based on Dodecanuclear Dy-Hydroxo Wheel Cluster with Slow Relaxation of Magnetization[J]. Inorg. Chem., 2014, 53(23):  12234-12236. doi: 10.1021/ic502042h

  27. [27]

      Wu Z L, Cui J Z, Wang W M, Kang X M, Shen H Y, Gao H L. Modulating Single-Molecule Magnet Behavior towards Multiple Magnetic Relaxation Processes through Structural Variation in Dy₄ Clusters[J]. Inorg. Chem. Front., 2018, 5(8):  1876-1885. doi: 10.1039/C8QI00214B

  28. [28]

      Wang W M, He L Y, Wang X X, Shi Y, Wu Z L, Cui J Z. Linear-Shaped Ln₄^Ⅲ and Ln₆^Ⅲ Clusters Constructed by a Polydentate Schiff Base Ligand and a β-Diketone Co-ligand: Structures, Fluorescence Properties, Magnetic Refrigeration and Single-Molecule Magnet Behavior[J]. Dalton Trans., 2019, 48:  16744-16755. doi: 10.1039/C9DT03478A

  29. [29]

      Wang W M, Wang S, Wu Z L, Ran Y G, Ren Y H, Zhang C F, Fang M. Two Phenoxo-O Bridged Dy₂ Complexes Based on 8-Hydroxyquinolin Derivatives with Different Magnetic Relaxation Features[J]. Inorg. Chem. Commun., 2017, 76:  48-51. doi: 10.1016/j.inoche.2017.01.001

  30. [30]

      Wang W M, Shi X H, Zhang H X, Wu M M, He Y L, Fang M, Shi Y, Fang M. Structures, Fluorescence Properties and Magnetic Properties of a Series of Dinuclear Lanthanide(Ⅲ) Compounds: Dy₂ Compound Showing Single-Molecule Magnet Behavior[J]. Polyhedron, 2018, 141(15):  304-308.

  31. [31]

      Li R F, Li R H, Liu X F, Chang X H, Feng X. Lanthanide Complexes Based on a Conjugated Pyridine Carboxylate Ligand: Structures, Luminescence and Magnetic Properties[J]. RSC Adv., 2020, 10(11):  6192-6199. doi: 10.1039/C9RA10975G

  32. [32]

      Wang W M, Wang Q, Bai L, Qiao H, Zhao X Y, Xu M, Liu S Y, Shi Y, Fang M, Wu Z L. Lanthanide-Directed Fabrication of Three Phenoxo-O Bridged Dinuclear Compounds Showing Magnetic Refrigeration and Single-Molecule Magnet Behavior[J]. Polyhedron, 2018, 142:  43-48. doi: 10.1016/j.poly.2017.12.017

  33. [33]

      Chen H H, Wu D F, Duan Y Y, Li L, Wang Y J, Zhang X M, Cui J Z, Gao H L. 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[J]. New J. Chem., 2020, 44(6):  2561-2570. doi: 10.1039/C9NJ05571A

  34. [34]

      Hahn P, Peng Y, Powell A K, Ullmann S, Klose J, Kersting B. Dinuclear Tb and Dy Complexes Supported by Hybrid Schiff-Base/Calixarene Ligands: Synthesis, Structures and Magnetic Properties[J]. Dalton Trans., 2020, 49(31):  10901-10908. doi: 10.1039/D0DT02209H

  35. [35]

      Ke H K, Yang Y S, Wei W, Jiang Y D, Zhang Y Q, Xie G, Chen S P. Synergistic Effect of Mixed Ligands on the Anisotropy Axis of Two Dinuclear Dysprosium Complexes[J]. Dalton Trans., 2020, 49(30):  10594-10602. doi: 10.1039/D0DT02139C

  36. [36]

      Guo P H, Jiang L, Wu Z H, Yan H, Chen Y C, Jia J H, Tong M L. Single-Molecule-Magnet Behavior in a [2×2] Grid Dy^Ⅲ₄ Cluster and a Dysprosium-Doped Y^Ⅲ₄ Cluster[J]. Inorg. Chem., 2015, 54(16):  8087-8092. doi: 10.1021/acs.inorgchem.5b01322

  37. [37]

      Cui J Z, Zhao B, Wang W M, Qiao W Z, Zhang H X, Wang S Y, Nie Y Y, Chen H M, Liu Z, Gao H L. Structures and Magnetic Properties of Several Phenoxo-O Bridged Dinuclear Lanthanide Complexes: Dy Derivatives Displaying Substituent Dependent Magnetic Relaxation Behavior[J]. Dalton Trans., 2016, 45(19):  8182-8191. doi: 10.1039/C6DT00220J

  38. [38]

      Wang W M, Wu Z L, Cui J Z. Molecular Assemblies from Linear-Shaped Ln₄ Clusters to Ln₈ Clusters Using Different β-Diketonates: Disparate Magnetocaloric Effects and Single-Molecule Magnet Behaviours[J]. Dalton Trans., 2021, 50:  12931-12943. doi: 10.1039/D1DT01344K

  39. [39]

      Wang W M, Wang S Y, Zhang H X, Shen H Y, Zou J Y, Gao H L, Cui J Z, Zhao B. Modulating Single-Molecule Magnet Behaviour of Phenoxo-O Bridged Lanthanide(Ⅲ) Dinuclear Complexes by Using Different β-Diketonate Coligands[J]. Inorg. Chem. Front., 2016, 3:  133-141.

  40. [40]

      Wu Z L, Zhang X T, Wang W M, Wang M J, Hao S S, Shen Q Y, Wang M L, Liu Q L, Guan X F. 'Windmill'-Shaped Ln^Ⅲ₄ (Ln^Ⅲ=Gd and Dy) Clusters: Magnetocaloric Effect and Single-Molecule-Magnet Behavior[J]. New J. Chem., 2020, 44(11):  4631-4638. doi: 10.1039/C9NJ05317D

  41. [41]

      Meihaus K R, Minasian S G, Lukens W W, Kozimor S A, Shuh D K, Tyliszczak T, Long J R. Influence of Pyrazolate vs N-Heterocyclic Carbene Ligands on the Slow Magnetic Relaxation of Homoleptic Trischelate Lanthanide(Ⅲ) and Uranium(Ⅲ) Complexes[J]. J. Am. Chem. Soc., 2014, 136(16):  6056-6068. doi: 10.1021/ja501569t

• 

  Scheme 1  Structure of H₂L

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Synthesis of H₂L

  下载: 全尺寸图片 幻灯片
  

  Scheme 3  Synthesis of complexes 1 and 2

  下载: 全尺寸图片 幻灯片
  

  Figure 1  Molecular structure of 1 shown with 30% probability displacement ellipsoids

  All hydrogen atoms are omitted for clarity; Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Coordination environment of Dy₂; (b) Geometric polyhedron of Dy₂ ions observed in complex 1

  Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Coordination modes for L^2- and dbm^-

  Symmetry code: a: -x, -y, 1-z

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Temperature dependence of χ_MT at 1 000 Oe for complex 1

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Temperature-dependence of χ′ and χ″ components of the ac magnetic susceptibility for 1 under 5 000 Oe dc field with an oscillation of 3.0 Oe

  下载: 全尺寸图片 幻灯片
  

  Figure 6  Plot of ln τ vs T^-1 fitting to the Arrhenius law for complex 1

  下载: 全尺寸图片 幻灯片
  

  Figure 7  Frequency dependence of χ′ and χ″ for 1 at 2.0-14.0 K under a zero dc field

  下载: 全尺寸图片 幻灯片
  

  Figure 8  Cole-Cole plots for 1 measured under a zero dc field

  Red solid lines are the best fitting to the experimental data, obtained with the generalized Debye model with α=0.17-0.65 for 1

  下载: 全尺寸图片 幻灯片

  Table 1.  Crystallographic data and structure refinements for complexes 1 and 2

  Parameter	1	2
  Formula	C64H60Dy2N6O14	C64H60Nd2N6O14
  Formula weight	1 462.18	1 425.66
  T/K	150.0	150
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a/nm	1.303 26(4)	1.311 32(10)
  b/nm	1.421 83(4)	1.427 74(10)
  c/nm	1.880 84(5)	1.880 80(12)
  α/(°)	100.036 0(12)	99.822(4)
  β/(°)	102.275 7(12)	102.555(5)
  γ/(°)	114.247 9(12)	113.953(5)
  V/nm3	2.968 23(15)	3.005 9(4)
  Z	2	2
  Crystal size/mm	0.36×0.31×0.28	0.37×0.26×0.13
  Dc/(g·cm-3)	1.636	1.575
  μ/mm-1	2.570	13.619
  Limiting indices	-16 ≤ h ≤ 16, -17 ≤ k ≤ 17, -23 ≤ l ≤ 23	-16 ≤ h ≤ 16, -17 ≤ k ≤ 17, -23 ≤ l ≤ 17
  Reflection collected	74 997	37 740
  Unique reflection	12 159	12 168
  Parameter	787	787
  Rint	0.045 1	0.078 4
  GOF on F2	1.073	1.006
  R1, wR2 [I > 2σ(I)]	0.026 4, 0.068 6	0.054 4, 0.140 8
  R1, wR2 (all data)	0.036 5, 0.073 3	0.068 0, 0.154 8

  下载: 导出CSV

  Table 2.  Comparison of energy barrier (ΔE/k_B) of recently reported Dy₂ SMMs and complex 1 in this work

  Dy2-SMM	ΔE/kB/K	Reference
  [Dy2(hfac)4(L)2]	6.77	[29]
  [Dy2(L1)2(hfac)6]·C7H16	6.81	[30]
  [Dy2(tmhd)2L2(CH3OH)2]	13.14	[31]
  {[Dy2(bpda)3(H2O)3]4·2H2O}	1.14	[32]
  [Dy(bfa)2L]2	24.3	[33]
  [Dy2(dbm)4L·CH3OH]	28	[34]
  [Dy2(L2)2]	33	[35]
  Dy2(L1)2(L2)2(CH3CH2OH)(CH3OH)	61	[36]
  [Dy2(dbm)2(L)2(C2H5OH)2]	56.77	This work

  下载: 导出CSV
•