English

• 0.   Introduction

  In recent years, the studies of lanthanide-based compounds have attracted increasing attention of chemists and material scientists not only due to their beauty and fascinating crystal structures^[1] but also because of the potential applications in functional materials, including interesting magnetic properties, luminescence properties, and catalysis^[2-4]. Among these potential applications of lanthanide-based compounds, the molecular-based magnetic material is one of the research hotspots for inorganic chemistry and material chemistry^[5], and magnetic refrigeration and singlemolecule magnets (SMMs) are particularly attractive^[6-9]. Key to the potential magnetic refrigeration application of a molecular-based magnetic material is its large magnetocaloric effect (MCE) ^[10], and an excellent magnetic refrigeration material featuring large MCE should possess negligible magnetic anisotropy and a large magnetic density^[11]. Hence, the isotropic Gd(Ⅲ) ion with a high spin state (S=7/2) is the best candidate for designing and constructing Gd(Ⅲ)-based compounds, which would be a promising magnetic refrigerant material to perform significant MCE ^[12]. Based on this, lots of poly-nuclear or highnuclear Gd (Ⅲ)-based clusters with fascinating structures and larger MCE have been reported over the past decade^[13-16]. It is worth mentioning that Long, Tong, and Zheng' s group have conducted outstanding work on the magnetic refrigeration materials of Gd (Ⅲ)-based clusters^[17-19]. These studies inspire and promote the synthesis of lanthanide-based compounds with outstanding and excellent magnetic refrigeration materials.

  It is well-known that the Schiff base ligand is a type of classical ligand. In the past decade, lots of Ln(Ⅲ)-based compounds with novel topologies and showing outstanding magnetic properties have been constructed by using Schiff base ligands^[20-23]. Considering the advantage of Schiff base ligands, we design and synthesize an organic polydentate Schiff base ligand (H₂L= pyridine-2-carboxylic acid (3, 5-di-tert-butyl-2-hydroxybenzylidene)-hydrazide, Scheme 1) which possesses abundant coordination sites, strong chelating ability, and various coordination patterns. When H₂L reacted with Gd(dbm)₃·2H₂O (Hdbm=dibenzoylmethane) or Gd(NO)₃·6H₂O, two new Gd₂ complexes with the molecular formulas [Gd₂(L)₂(dbm)₂(C₂H₅OH)₂] (1) and [Gd₂(L)₂(HL)₂(DMF)] ·2CH₃CN (2) (DMF=N, N-dimethylformamide) have been synthesized through a solvothermal method. The structural and magnetic properties of 1 and 2 were deeply investigated and discussed. The magnetic study revealed that complexes 1 and 2 show MCE with-ΔS_m of 20.16 J·K^-1·kg^-1 for 1 and 17.14 J·K^-1·kg^-1 for 2 at ΔH=70 kOe and T=2.0 K.

  Scheme 1

  

  Scheme 1.  Structure of organic polydentate Schiff base H₂L

  下载: 全尺寸图片 幻灯片

  1.   Experimental

  1.1   Materials and measurements

  Gadolinium nitrate hexahydrate (Gd(NO₃)₃·6H₂O) was bought from Energy Chemical Co., Ltd. DMF, ethanol, acetonitrile, and other solvents were purchased from Fuchen chemical corporation. Hdbm, picolinohydrazide, and 3, 5-di-tert-butylsalicylaldehyde were purchased from Aladdin Reagent (Shanghai) Co., Ltd. Gd(dbm)₃·2H₂O and polydentate Schiff base ligand H₂L were prepared by using an already reported literature method^[24-25]. The elemental analyses (C, H, and N) of complexes 1 and 2 were performed on a PerkinElmer 240 CHN elemental analyzer. Magnetic properties for complexes 1 and 2 were measured using a Quantum Design MPMS-XL7 and a PPMS-9 ACMS magnetometer. Diamagnetic corrections were estimated with Pascal's constants for all atoms^[26].

  1.2   Syntheses of complexes 1 and 2

  [Gd₂(L)₂(dbm)₂(C₂H₅OH)₂] (1): H₂L (0.05 mmol), Gd(dbm)₃·2H₂O (0.05 mmol), ethanol (6.0 mL), and acetonitrile (5.0 mL) were enclosed in a glass vial (20 mL), and then the mixture was heated to 70 ℃ and keep at this temperature for 72 h, and then the temperature was dropped to room temperature slowly. Yellow block crystals suitable for X-ray diffraction were obtained. Yields based on Gd(dbm)₃·2H₂O: 41%. Elemental analysis Calcd. for C₇₆H₈₄Gd₂N₆O₁₀(%): C 58.61, H 5.40, N 5.40; Found(%): C 58.65, H 5.37, N 5.44.

  [Gd₂(L)₂(HL)₂(DMF)] ·2CH₃CN (2): H₂L (0.03 mmol), Gd(NO₃)₃·6H₂O (0.03 mmol), ethanol (3.0 mL), DMF (2.0 mL), and acetonitrile (2.0 mL) were added to a three flask and stirred at room temperature for about 3 h. Then the mixture was sealed in a 15 mL glass bottle and heated to 80 ℃ to react for 48 h and then slowly cooled to room temperature subsequently. Yellow block crystals suitable for X-ray diffraction were obtained. Yields based on Gd(NO₃)₃·6H₂O: 32%. Elemental analysis Calcd. for C₉₁H₁₁₅Gd₂N₁₅O₉(%): C 58.16, H 6.13, N 11.19; Found(%): C 58.11, H 6.17, N 11.25.

  1.3   X-ray crystallography

  The crystallographic diffraction data for complexes 1 and 2 were collected on a Bruker SMART APEX Ⅱ CCD diffractometer equipped with graphite monochromatized Mo Kα radiation (λ =0.071 073 nm) by using φ-ω scan mode. Multi-scan absorption correction was applied to the intensity data using the SADABS program. The structures were solved by direct methods and refined by full-matrix least-squares on F² using the SHELXTL (Olex 2) program^[27]. All non-hydrogen atoms were refined anisotropically. All the other H atoms were positioned geometrically and refined using a riding model. Due to the existence of disordered solvent molecules in the crystals of 1 and 2, we remove the disordered solvent molecules by using PLATON/ SQUEEZE program. To determine the specific number of free solvent molecules, the thermogravimetric analysis (TGA) of the crystal samples for 1 and 2 have been measured. Details of the crystal data and structure refinement parameters for complexes 1 and 2 are summarized in Table 1, and selected bond lengths and angles of complexes 1 and 2 are listed in Table S1 and S2 (Supporting information).

  表 1

  

  表 1  Crystal data and structure refinement parameters for 1 and 2

  下载: 导出CSV

  Parameter	1	2
  Formula	C76H84Gd2N6O10	C91H115Gd2N15O9
  Formula weight	1 555.99	1 877.42
  T/K	150.0	150.0
  Crystal system	Monoclinic	Monoclinic
  Space group	P21/c	P21/c
  a / nm	1.230 26(2)	2.068 43(6)
  b / nm	1.536 69(2)	1.985 86(5)
  c / nm	1.869 93(3)	2.467 71(8)
  β/(°)	97.916 1(6)	91.634 0(11)
  V /nm3	3.501 47(9)	10.132 3(5)
  Z	2	4
  Crystal size / mm	0.36×0.21×0.14	0.26×0.13×0.11
  Dc(g.cm-3)	1.476	1.204
  μ/ mm-1	1.940	1.353
  Limiting indices	-15 ≤ h ≤ 14, -19 ≤ k ≤ 19, -23 ≤ l ≤ 23	-25 ≤ h ≤ 25, -24 ≤ k ≤ 24, -30 ≤ l ≤ 30
  Reflection collected	44 308	144 368
  Unique	7 178	20 725
  Parameter	434	1 054
  Rint	0.036 5	0.084 8
  GOF on F 2	1.042	1.082
  R1, wR2 [I>2σ(I)]	0.023 6, 0.056 6	0.046 1, 0.108 9
  R1, wR2 (all data)	0.030 8, 0.060 9	0.068 7, 0.119 9

  CCDC: 2111657, 1; 2111658, 2.

  2.   Results and discussion

  2.1   Crystal structures of complexes 1 and 2

  Single-crystal X-ray diffraction analyses reveal that both complexes 1 and 2 crystallize in the monoclinic space group P2₁/c (Table 1). As shown in Fig. 1, the structure of 1 contains two Gd(Ⅲ) ions, two L^2- ions, two dbm^- ions, and two coordinated C₂H₅OH molecules. Each central Gd(Ⅲ) ion in complex 1 is coordinated by six oxygen atoms (O1, O1a, O2, O3, O4, and O5) and two nitrogen atoms (N1 and N3) forming an O₆N₂ coordination environment (Fig.S1). As shown in Fig.S2, the eight-coordinate Gd1 ion shows a distorted triangular dodecahedron (D_2h) coordination geometry. It is also confirmed by using SHAPE 2.0 software (Table 2) ^[28]. The coordination modes of L^2- and dbm^- are shown in Fig. 2. L^2- adopts a quad-dentate chelation model to connect the central Gd(Ⅲ) ion, and dbmadopts a bidentate chelation model to connect the central Gd (Ⅲ) ion. The Gd1 and Gd1a ions are connected by two μ₂-O (O1 and O1a) atoms forming a parallelogram Gd₂O₂ core. The Gd1…Gd1a distance is 0.405 2(9) nm, which is slightly larger than those of some reported Gd₂ complexes^[29-32]. In addition, the Gd1—O1—Gd1a angle in the Gd₂O₂ core is 114.90(7)°. In 1, the Gd—O distances fall in a range of 0.222 3(2)-0.243 1(7) nm, and the Gd1—N1, Gd1—N3 bond lengths are 0.257 9(2) and 0.247 6(2) nm, respectively. The O—Gd—O bond angles fall in a range of 65.09(7)°-146.46(6)°.

  图 1

  

  图 1.  Molecular structure of complex 1 shown with 50% probability displacement ellipsoids

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

  下载: 全尺寸图片 幻灯片

  表 2

  

  表 2  Gd^Ⅲ ion geometry analysis by SHAPE 2.0 for 1^*

  下载: 导出CSV

  GdⅢ ion	D4d SAPR-8	D2d TDD-8	C2v JBTPR-8	C2v BTPR-8	D2d JSD-8
  Gd1	3.696	2.053	4.054	2.901	5.227
  * SAPR-8=square antiprism; TDD-8=triangular dodecahedron; JBTPR-8=biaugmented trigonal prism J50; BTPR-8=biaugmented trigonal prism; JSD-8=snub diphenoid J84.

  图 2

  

  图 2.  Coordination mode of L^2- (a) and dbm^- (b) in 1

  H atoms of C—H bonds are omitted for clarity; Symmetry code: a: 1-x, 1-y, 1-z

  下载: 全尺寸图片 幻灯片

  Different from 1, complex 2 is mainly composed of two Gd (Ⅲ) ions, two L^2- ions, two HL^- ions, and one coordinated DMF molecule (Fig. 3). Both Gd1 and Gd₂ ions in complex 2 are nine-coordinate, and each Gd(Ⅲ) ion is coordinated by six oxygen atoms and three nitrogen atoms forming an N₃O₆ coordination environment (Fig.S3). Accordingly, as shown in Fig.S4, both of the nine-coordinate Gd(Ⅲ) centers lie in a distorted spherical capped square antiprism (C_4v) which also can be calculated by using SHAPE 2.0 software (Table 3). There are two coordination modes for L^2- and HL^- in 2 (Fig. 4): quad-dentate or tri-dentate chelation model to connect the central Gd(Ⅲ) ion, respectively. The two Gd(Ⅲ) ions are connected by three μ₂-O (O3, O5, and O9) atoms forming a triangular biconical-shaped Gd₂O₃ core. The distance of the two central Gd(Ⅲ) ions is 0.392 3(3) nm, which is smaller than that of complex 1. The Gd1— O3—Gd2, Gd1—O9—Gd2, and Gd1—O9—Gd2 angles in the Gd₂O₃ core are 105.68(3)°, 98.64(6)°, and 106.95(4)°, respectively, which are also smaller than those of complex 1. The Gd—O bond lengths are in a range of 0.225 3(3)-0.260 7(4) nm, while the average Gd—N distance is 0.261 2(1) nm. The O—Gd—O bond angles fall in a range of 61.96(10)°-149.73(12)°.

  图 3

  

  图 3.  Molecular structure of the complex 2 shown with 50% probability displacement ellipsoids

  H atoms are omitted for clarity

  下载: 全尺寸图片 幻灯片

  表 3

  

  表 3  Gd^Ⅲ ion geometry analysis by SHAPE 2.0 for 2^*

  下载: 导出CSV

  GdⅢ ion	C4v JCSAPR-9	C4v CSAPR-9	D3h JTCTPR-9	D3h TCTPR-9	Cs MFF-9
  Gd1	1.93	1.301	3.129	1.611	1.588
  Gd2	2.165	1.492	3.521	1.824	1.604
  *JCSAPR-9=capped square antiprism J10; CSAPR-9=spherical capped square antiprism; JTCTPR-9=tricapped trigonal prism J51;TCTPR-9=spherical tricapped trigonal prism; MFF-9=muffin.

  图 4

  

  图 4.  Coordination mode of L^2- (a) and HL^- (b) in 2

  H atoms of C—H bonds are omitted for clarity

  下载: 全尺寸图片 幻灯片

  2.2   TGA of complexes 1 and 2

  To study the thermal stabilities of complexes 1 and 2, TGA was performed and the curves are shown in Fig.S5 and S6. For 1, the weight loss of 5.78% (Calcd. 5.91%) between 26 and 285 ℃ can be attributed to the loss of two coordinated EtOH molecules. After that complex 1 started to decompose. For 2, the weight loss of 4.11% from 26 to 245 ℃ is attributed to the loss of two free CH₃CN molecules (Calcd. 4.36%). Thereafter, a weight loss of 3.92% (Calcd. 3.88%) occurred, which is attributed to the loss of a coordinated DMF molecule. Subsequently, complex 2 gradually decomposed in a temperature range of 280-800 ℃.

  2.3   Magnetic properties of complexes 1 and 2

  Direct current (dc) magnetic susceptibility measurements for the two Gd₂ complexes 1 and 2 were performed on polycrystalline samples during a temperature range of 300.0-2.0 K under an applied field of 1 kOe. The χ_ΜT vs T plots for complexes 1 and 2 are shown in Fig. 5. The room-temperature χ_ΜT products of 1 and 2 were 15.80 and 15.78 cm³·K·mol^-1, respectively, which are in good agreement with the expected value (15.76 cm³·K·mol^-1) for two uncoupled Gd (Ⅲ) ions (⁸S_7/2, g=2). As the temperature decreased, the χ_ΜT values of 1 and 2 slowly declined during the temperature range of 300.0-25.0 K. Thereafter, the χ_ΜT values of 1 and 2 quickly dropped to a minimum of 11.58 and 5.68 cm³·K·mol^-1 at 2.0 K. The downward trend of the χ_ΜT vs T curves implies that there is an antiferromagnetic (AF) interaction between adjacent Gd (Ⅲ) ions in the two Gd₂ complexes 1 and 2^[33].

  图 5

  

  图 5.  Temperature dependence of χ_MT products at 1.0 kOe for 1 (a) and 2 (b)

  下载: 全尺寸图片 幻灯片

  The Curie-Weiss law was used for fitting the magnetic susceptibility of complexes 1 and 2 (Fig. S7 and S8). The two parameters, C=15.84 cm³·K·mol^-1 and θ= -1.84 K (R²=0.999 9) for 1 and C=15.91 cm³·K·mol^-1 and θ=-5.43 K (R²=0.999 51) for 2 were obtained. The negative θ values of 1 and 2 further suggest that there is an antiferromagnetic interaction between adjacent Gd(Ⅲ) ions in 1 and 2^[34].

  The magnetization data for the two Gd₂ complexes 1 and 2 were collected at 2.0-10.0 K in the 0-70 kOe field. As depicted in Fig.S9, the M values for complexes 1 and 2 rapidly increased below 20 kOe and then steadily increased to 14.13Nβ for 1 and 14.07Nβ for 2 at 70 kOe, which are very close to the saturation value of 14Nβ for two isolated Gd(Ⅲ) (S=7/2, g=2) ions.

  According to the previously reported literature^[35-37], because of the larger isotropic and high-spin ground state of Gd(Ⅲ) ion, the MCE of both 1 and 2 was studied. The maximum magnetic entropy change (-ΔS_m) of 1 and 2 were calculated by using the Maxwell equation: ΔS_m(T) =∫[∂M (T, H)/∂T] _H dH^[38]. The -ΔS_m vs T curves of 1 and 2 are shown in Fig. 6. The observed-ΔS_m values of 1 and 2 were 20.16 and 17.14 J·K^-1· kg^-1 at ΔH=70 kOe and T=2.0 K, which were smaller than the theoretical values of 22.22 J·K^-1·kg^-1 for 1 and 18.83 J·K^-1·kg^-1 for 2 (based on the equation -ΔS_m=2Rln(2S+1)/M_r, S_Gd=7/2, and R=8.314 J·mol^-1·K^-1). The difference between experimental and theoretical -ΔS_m values may be due to the antiferromagnetic interaction between Gd (Ⅲ) ions in 1 and 2^[39]. To better compare and display the -ΔS_m values of Gd₂ complexes, the -ΔS_m values of recently reported dinuclear Gd (Ⅲ)-based complexes are listed in Table 4^[40-49]. The -ΔS_m of 2 was smaller than some reported Gd₂ complexes, however, it is worth mentioning that the -ΔS_m of complex 1 was larger than those of some dinuclear Gd (Ⅲ)-based complexes. The reason for the larger -ΔS_m of complex 1 may be due to the weak antiferromagnetic interaction and the smaller M_r/N_Gd ratio of 1.

  图 6

  

  图 6.  Plots of -ΔS_m vs T for 1 (a) and 2 (b)

  下载: 全尺寸图片 幻灯片

  表 4

  

  表 4  Comparison of -ΔS_m values for complexes 1, 2 and some reported Gd₂ complexes

  下载: 导出CSV

  Dinuclear G(Ⅲ)-based complex	Mr	Magnetic interaction	-ΔSm/(J.K-l.kg-1)	ΔH/kOe	Ref.
  [Gd2(bfa)4(L)2].CH2Cl2a	1 747.16	AF (no J value reported)	18.5	70	[40]
  [Gd2(hfac)4(L)2]b	1 795.07	AF (J=-0.07 cm-1)	15.00	80	[41]
  [Gd(hfac)2(L)]2c	1 693.37	AF (J=-0.04 cm-1)	19.94	70	[42]
  [Gd2(dbm)4(L)2]d	1791.99	AF (no J value reported)	14.36	70	[43]
  [Gd2(hfac)4(L1)2]e	1 665.32	AF (J=-0.13 cm-1)	17.66	70	[44]
  [Gd2(hfac)4(L2)2]f	1 693.37	AF(J=-0.10cm-1)	14.81	70	[44]
  [Gd2(L1)2(tmhd)2(CH3O)2]g	1 670.21	AF (no J value reported)	18.59	70	[45]
  [Gd(bfa)2(L)]2h	1 681.61	AF (no J value reported)	17.78	70	[46]
  [Gd2(L)2(dbm)2(H2O)2]·CH3OHi	1 395.57	AF (J=-0.045 cm-1)	23.2	70	[47]
  [Gd2(dbm)2(L)2(CH3OH)2]j	1 445.76	AF (no J value reported)	21.1	70	[48]
  [Gd(OAc)3(H2O2]2-4H2O	2 474.95	F (J/kB=0.068(2) K)	40	70	[49]
  Complex 1	1 555.99	AF (no J value reported)	20.16	70	This work
  Complex 2	1 836.42	AF (no J value reported)	17.14	70	This work
  a HL=2-(((4-methylphenyl)imino)methyl)-8-hydroxyquinoline; b HL=2-((4-bromo-phenylimino)-methyl)-quinolin-8-ol; c HL=2-((4-ethylphenyl)imino)methyl-8-hydroxyquinoline; d HL=2-((4-nitrophenyl)imino)methyl-8-hydroxyquinoline; e HL1=2-(4-methylaniline-imino)methyl)-8-hydroxyquinoline; f HL2=2-((3, 4-dimethylaniline)-imino)methyl)-8-hydroxyquinoline; g HL1=bis-Schiff base ligand; h HL=2-(5-methyl-1, 2-oxazol-imino)methyl)-8-hydroxyquinoline; i HL=2-((1E)-(((pyridin-2-yl)formamido)imino)methyl)benzoic acid; j HL=N'-(4-(diethylamino)salicylaldehyde)pyridyl-2-carbohydrazide.

  3.   Conclusions

  In summary, we have synthesized two new Gd₂ complexes [Gd₂(L)₂(dbm)₂(C₂H₅OH)₂] (1) and [Gd₂(L)₂(HL)₂(DMF)] ·2CH₃CN (2). Both complexes 1 and 2 are binuclear structures with different coordination environments of central Gd(Ⅲ) ions. Magnetic measurements imply that the two Gd₂ complexes display magnetic refrigeration properties. Our present work provides a new approach to design and construct Gd(Ⅲ)-based magnetic refrigeration materials. Magnetic refrigeration studies of other poly-nuclear or high-nuclear Gd(Ⅲ)-based clusters are underway in our group.

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

  
  
• 1. [1]

     Li X Y, Su H F, Li Q W, Feng R, Bai H Y, Chen H Y, Xu J, Bu X H. A Giant Dy₇₆ Cluster: A Fused Bi-nanopillar Structural Model for Lanthanide Clusters[J]. Angew. Chem. Int. Ed., 2019, 58:  10184-10188. doi: 10.1002/anie.201903817

  2. [2]

     Ishikawa N, Sugita M, Ishikawa T, Koshihara S, Kaizu Y. Lanthanide Double-Decker Complexes Functioning as Magnets at the Single-Molecular Level[J]. J. Am. Chem. Soc., 2003, 125:  8694-8695. doi: 10.1021/ja029629n

  3. [3]

     Mahata P, Mondal S K, Singha D K, Majee P. Luminescent Rare-Earth-Based MOFs as Optical Sensors[J]. Dalton Trans., 2017, 46:  301-328. doi: 10.1039/C6DT03419E

  4. [4]

     Dong J, Cui P, Shi P F, Cheng P, Zhao B. Ultrastrong Alkali-Resisting Lanthanide-Zeolites Assembled by[Ln₆₀] Nanocages[J]. J. Am. Chem., Soc., 2015, 137:  15988-15991. doi: 10.1021/jacs.5b10000

  5. [5]

     Zheng X Y, Kong X J, Zheng Z P, Long L S, Zheng L S. High-Nuclearity Lanthanide-Containing Clusters as Potential Molecular Magnetic Coolers[J]. Acc. Chem. Res., 2018, 51:  517-525. doi: 10.1021/acs.accounts.7b00579

  6. [6]

     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

  7. [7]

     Xu C Y, Wu Z L, Fan C J, Yan L L, Wang W M, Ji B M. Synthesis of Two Lanthanide Clusters Ln₄^Ⅲ (Gd₄ and Dy₄) with[2×2] Square Grid Shape: Magnetocaloric Effect and Slow Magnetic Relaxation Behaviors[J]. J. Rare Earths, 2021, 39:  1082-1088. doi: 10.1016/j.jre.2020.08.015

  8. [8]

     Bar A K, Kalita P, Singh M K, Rajaraman G, Chandrasekhar V. Low-Coordinate Mononuclear Lanthanide Complexes as Molecular Nanomagnets[J]. Coord. Chem. Rev., 2018, 367:  163-216. doi: 10.1016/j.ccr.2018.03.022

  9. [9]

     Wang W M, Qiao W Z, Zhang H X, Wang S Y, Nie Y Y, Chen H M, Liu Z, Gao H L, Cui J Z, Zhao B. 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:  8182-8191. doi: 10.1039/C6DT00220J

  10. [10]

      Luo X M, Hu Z B, Lin Q F, Cheng W W, Cao J P, Cui C H, Mei H, Song Y, Xu Y. Exploring the Performance Improvement of Magnetocaloric Effect Based Gd-Exclusive Cluster Gd₆₀[J]. J. Am. Chem. Soc, 2018, 140:  11219-11222. doi: 10.1021/jacs.8b07841

  11. [11]

      Chen Y C, Qin L, Meng Z S, Yang D F, Wu C, Fu Z D, Zheng Y Z, Liu J L, Tarasenko R, Orendác M, Prokleška J, Sechovský V, Tong M L. Study of a Magnetic-Cooling Material Gd(OH)CO₃[J]. J. Mater. Chem. A, 2014, 2:  9851-9858. doi: 10.1039/C4TA01646G

  12. [12]

      Zhang Z M, Zangana K H, Kostopoulos A K, Tong M L, Winpenny R E P. A Pseudo-Icosahedral Cage {Gd₁₂} Based on Aminomethylphosphonate[J]. Dalton Trans., 2016, 45:  9041-9044. doi: 10.1039/C6DT00876C

  13. [13]

      Zheng X Y, Jiang Y H, Zhuang G L, Liu D P, Liao H G, Kong X J, Long L S, Zheng L S. A Gigantic Molecular Wheel of {Gd₁₄₀}: A New Member of the Molecular Wheel Family[J]. J. Am. Chem. Soc., 2017, 139:  18178-18181. doi: 10.1021/jacs.7b11112

  14. [14]

      Wang W M, Yue R X, Gao Y, Wang M J, Hao S S, Shi Y, Kang X M, Wu Z L. Large Magnetocaloric Effect and Remarkable Single-Molecule-Magnet Behavior in Triangle-Assembled Ln₆^Ⅲ Clusters[J]. New J. Chem., 2019, 43:  16639-16646. doi: 10.1039/C9NJ03921J

  15. [15]

      Zheng X Y, Peng J B, Kong X J, Long L S, Zheng L S. Mixed-Anion Templated Cage-like Lanthanide Clusters: Gd₂₇ and Dy₂₇[J]. Inorg. Chem. Front., 2016, 3:  320-325. doi: 10.1039/C5QI00249D

  16. [16]

      Guo F S, Chen Y C, Mao L L, Lin W Q, Leng J D, Tarasenko R, Orendác M, Prokleška J, Sechovský V, Tong M L. Anion-Templated Assembly and Magnetocaloric Properties of a Nanoscale {Gd₃₈} Cage versus a {Gd₄₈} Barrel[J]. Chem. Eur. J., 2013, 19:  14876-14885. doi: 10.1002/chem.201302093

  17. [17]

      Peng J B, Kong X J, Zhang Q C, Orendác M, Prokleška J, Ren Y P, Long L S, Zheng Z P, Zheng L S. Beauty, Symmetry, and Magnetocaloric Effect-Four-Shell Keplerates with 104 Lanthanide Atoms[J]. J. Am. Chem. Soc., 2014, 136:  17938-17941. doi: 10.1021/ja5107749

  18. [18]

      Chen Y C, Prokleška J, Xu W J, Liu J L, Liu J, Zhang W X, Jia J H, Sechovský V, Tong M L. A Brilliant Cryogenic Magnetic Coolant: Magnetic and Magnetocaloric Study of Ferromagnetically Coupled GdF₃[J]. J. Mater. Chem. C, 2015, 3:  12206-12211. doi: 10.1039/C5TC02352A

  19. [19]

      Zheng Y Z, Zhou G J, Zheng Z P, Winpenny R E P. Molecule-Based Magnetic Coolers[J]. Chem. Soc. Rev., 2014, 43:  1462-1475. doi: 10.1039/C3CS60337G

  20. [20]

      Wu J F, Li X L, Zhao L, Guo M, Tan J K. Enhancement of Magnetocaloric Effect through Fixation of Carbon Dioxide: Molecular Assembly from Ln₄ to Ln₄ Cluster Pairs[J]. Inorg. Chem., 2017, 56:  4104-4111. doi: 10.1021/acs.inorgchem.7b00094

  21. [21]

      Xu C Y, Qiao X Y, Tan Y, Liu S S, Hou W Y, Cui Y Y, Wu W L, Hua Y P, Wang W M. 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

  22. [22]

      Li X L, Li H, 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:  20316-20320. doi: 10.1039/C5DT03931B

  23. [23]

      Wang W M, Li X Z, Zhang L, Chen J L, Wang J H, Wu Z L, Cui J Z. A Series of[2×2]Square Grid Ln₄^Ⅲ Clusters: A Large Magnetocaloric Effect and Single-Molecule-Magnet Behavior[J]. New J. Chem., 2019, 43:  7419-7426. doi: 10.1039/C8NJ04454F

  24. [24]

      Zhang L, Zhang P, Zhao L, Wu J F, Guo M, Tang J K. Anions Influence the Relaxation Dynamics of Mono-μ₃-OH-Capped Triangular Dysprosium Aggregates[J]. Inorg. Chem., 2015, 54:  5571-5578. doi: 10.1021/acs.inorgchem.5b00702

  25. [25]

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

  26. [26]

      Boudreaux E A, Mulay L N. Theory and Applications of Molecular Paramagnetism. New York: Wiley-Interscience, 1976.

  27. [27]

      Sheldrick G M. SHELX-97, Program for the Solution and the Refinement of Crystal Structures, University of Göttingen, Germany, 1997.

  28. [28]

      Zabrodsky H, Peleg S, Avnir D. Continuous Symmetry Measures. 2. Symmetry Groups and the Tetrahedron[J]. J. Am. Chem. Soc., 1993, 115:  8278-8289. doi: 10.1021/ja00071a042

  29. [29]

      Wang W M, Ren Y H, Wang S, Zhan C F, Wu Z L, Zhang H, Fang M. Lanthanide Dinuclear Complexes Constructed by 8-Hydroxyquinoline Schiff Base Showing Magnetic Refrigeration and Slow Magnetic Relaxation[J]. Inorg. Chim. Acta, 2016, 453:  452-456. doi: 10.1016/j.ica.2016.09.002

  30. [30]

      Wang W M, Liu S Y, Xu M, Bai L, Wang H Q, Wen X, Zhao X Y, Qiao H, Wu Z L. Structures and Magnetic Properties of Phenoxo-O-Bridged Dinuclear Lanthanide(Ⅲ) Compounds: Single-Molecule Magnet Behavior and Magnetic Refrigeration[J]. Polyhedron, 2018, 145:  114-119. doi: 10.1016/j.poly.2018.01.037

  31. [31]

      Wang W M, Zhang H X, Wang S Y, Shen H Y, Gao H L, Cui J Z, Zhao B. 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

  32. [32]

      Zhang S W, Shi W, Li L L, Duan E Y, Cheng P. Lanthanide Coordination Polymers with"fsy-type"Topology Based on 4, 4'-Azobenzoic Acid: Syntheses, Crystal Structures, and Magnetic Properties[J]. Inorg. Chem., 2014, 53:  10340-10346. doi: 10.1021/ic501395p

  33. [33]

      Guan X F, Shen J X, Hu X Y, Yang Y, Han X, Zhao J Q, Wang J, Shi Y, Wang W M. Synthesis, Structures and Magnetic Refrigeration Properties of Four Dinuclear Gadolinium Compounds[J]. Polyhedron, 2019, 166:  17-22. doi: 10.1016/j.poly.2019.03.022

  34. [34]

      Wang S Y, Wang W M, Zhang H X, Shen H Y, Jiang L, Cui J Z, Gao H L. Seven Phenoxido-Bridged Complexes Encapsulated by 8-Hydroxyquinoline Schiff Base Derivatives and β-Diketone Ligands: Single-Molecule Magnet, Magnetic Refrigeration and Luminescence Properties[J]. Dalton Trans., 2016, 45:  3362-337. doi: 10.1039/C5DT04391C

  35. [35]

      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

  36. [36]

      Wang K, Chen Z L, Zou H H, Zhang S H, Li Y, Zhang X Q, Sun W Y, Liang F P. Diacylhydrazone-Assembled {Ln₁₁} Nanoclusters Featuring a"Double-Boats Conformation"Topology: Synthesis, Structures and Magnetism[J]. Dalton Trans., 2018, 47:  2337-2343. doi: 10.1039/C7DT03179C

  37. [37]

      Wang K, Chen Z L, Zou H H, Hu K, Li H Y, Zhang Z, Sun W Y, Liang F P. A Single-Stranded {Gd₁₈} Nanowheel with a Symmetric Polydentate Diacylhydrazone Ligand[J]. Chem. Commun., 2016, 52:  8297-8300. doi: 10.1039/C6CC02208A

  38. [38]

      Luo Z R, Zou H H, Chen Z L, Li B, Wang K, Liang F P. Triethylamine-Templated Nanocalix Ln₁₂ Clusters of Diacylhydrazone: Crystal Structures and Magnetic Properties[J]. Dalton Trans., 2019, 48:  17414-17421. doi: 10.1039/C9DT03335A

  39. [39]

      Chang L X, Xiong G, Wang L, Cheng P, Zhao B. A 24-Gd Nanocapsule with a Large Magnetocaloric Effect[J]. Chem. Commun., 2013, 49:  1055-1057. doi: 10.1039/C2CC35800J

  40. [40]

      Wang W M, Duan W W, Yue L C, Wang Y L, Ji W Y, Zhang C F, Fang M, Wu Z L. Magnetic Refrigeration and Single-Molecule Magnet Behaviour of Two Lanthanide Dinuclear Complexes (Ln=Gd^Ⅲ, Tb^Ⅲ) Based on 8-Hydroxyquinolin Derivatives[J]. Inorg. Chim. Acta, 2017, 466:  145-150. doi: 10.1016/j.ica.2017.05.059

  41. [41]

      Chu X Y, Zhang H X, Chang Y X, Nie Y Y, Cui J Z, Gao H L. A Series of Ln₂ Complexes Based on an 8-Hydroxyquinoline Derivative: Slow Magnetization Relaxation and Photo-Luminescence Properties[J]. New J. Chem., 2018, 42:  5688-5697. doi: 10.1039/C7NJ04942K

  42. [42]

      Wang W M, Liu H H, He L T, Han X R, Wu Z L, Ran Y G, Zou J Y, Fang M. Structures, Luminescence Properties, Magnetocaloric Effect and Slow Magnetic Relaxation of Three Ln(Ⅲ) Complexes Based on 8-Hydroxyquinoline Schiff-Base Ligand[J]. Polyhedron, 2017, 133:  119-124. doi: 10.1016/j.poly.2017.04.034

  43. [43]

      Wu D F, Liu Z, Ren P, Liu X H, Wang N, Cui J Z, Gao H L. A New Family of Dinuclear Lanthanide Complexes Constructed from an 8-Hydroxyquinoline Schiff Base and β-Diketone: Magnetic Properties and Near-Infrared Luminescence[J]. Dalton Trans., 2019, 48:  1392-1403. doi: 10.1039/C8DT04384A

  44. [44]

      Wang W M, Guan X F, Liu X D, Fang M, Zhang C F, Fang M, Wu Z L. Two Gd₂ Compounds Constructed by 8-Hydroxyquinoline Schiff Base Ligands: Synthesis, Structure, and Magnetic Refrigeration[J]. Inorg. Chem. Commun, 2017, 79:  8-11. doi: 10.1016/j.inoche.2017.03.014

  45. [45]

      Xia Q Y, Feng M Y, Ma D X, Shi S M, Xie Y C, Tian W, Shi H J, Wang Q L, Wang W M. Structures, Luminescent Properties and Magnetic Refrigeration of Two Series of Ln₂^Ⅲ Compounds[J]. Polyhedron, 2019, 166:  141-145. doi: 10.1016/j.poly.2019.03.040

  46. [46]

      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

  47. [47]

      Shi Q H, Xue C L, Fan C J, Yan L L, Qiao N, Fang M, Wang S F. Magnetic Refrigeration Property and Slow Magnetic Relaxation Behavior of Five Dinuclear Ln (Ⅲ)-Based Compounds[J]. Polyhedron, 2021, 194:  114938-114944. doi: 10.1016/j.poly.2020.114938

  48. [48]

      Chang Y X, Hou F, Feng M Y, Zhang H H, Kang T T, Wang W M, Fang M. Two Dinuclear Lanthanide(Ⅲ) Compounds Based on a Multidentate Ligand: Structures, Magnetic Refrigeration and Slow Magnetic Relaxation[J]. Inorg. Chim. Acta, 2019, 486:  83-87. doi: 10.1016/j.ica.2018.10.045

  49. [49]

      Evangelisti M, Roubeau O, Palacios E, Camon A, Hooper T N, Brechin E K, Alonso J J. Cryogenic Magnetocaloric Effect in a Ferromagnetic Molecular Dimer[J]. Angew. Chem. Int. Ed., 2011, 50:  6606-6609. doi: 10.1002/anie.201102640

• 

  Scheme 1  Structure of organic polydentate Schiff base H₂L

  下载: 全尺寸图片 幻灯片
  

  图 1  Molecular structure of complex 1 shown with 50% probability displacement ellipsoids

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

  下载: 全尺寸图片 幻灯片
  

  图 2  Coordination mode of L^2- (a) and dbm^- (b) in 1

  H atoms of C—H bonds are omitted for clarity; Symmetry code: a: 1-x, 1-y, 1-z

  下载: 全尺寸图片 幻灯片
  

  图 3  Molecular structure of the complex 2 shown with 50% probability displacement ellipsoids

  H atoms are omitted for clarity

  下载: 全尺寸图片 幻灯片
  

  图 4  Coordination mode of L^2- (a) and HL^- (b) in 2

  H atoms of C—H bonds are omitted for clarity

  下载: 全尺寸图片 幻灯片
  

  图 5  Temperature dependence of χ_MT products at 1.0 kOe for 1 (a) and 2 (b)

  下载: 全尺寸图片 幻灯片
  

  图 6  Plots of -ΔS_m vs T for 1 (a) and 2 (b)

  下载: 全尺寸图片 幻灯片

  表 1  Crystal data and structure refinement parameters for 1 and 2

  Parameter	1	2
  Formula	C76H84Gd2N6O10	C91H115Gd2N15O9
  Formula weight	1 555.99	1 877.42
  T/K	150.0	150.0
  Crystal system	Monoclinic	Monoclinic
  Space group	P21/c	P21/c
  a / nm	1.230 26(2)	2.068 43(6)
  b / nm	1.536 69(2)	1.985 86(5)
  c / nm	1.869 93(3)	2.467 71(8)
  β/(°)	97.916 1(6)	91.634 0(11)
  V /nm3	3.501 47(9)	10.132 3(5)
  Z	2	4
  Crystal size / mm	0.36×0.21×0.14	0.26×0.13×0.11
  Dc(g.cm-3)	1.476	1.204
  μ/ mm-1	1.940	1.353
  Limiting indices	-15 ≤ h ≤ 14, -19 ≤ k ≤ 19, -23 ≤ l ≤ 23	-25 ≤ h ≤ 25, -24 ≤ k ≤ 24, -30 ≤ l ≤ 30
  Reflection collected	44 308	144 368
  Unique	7 178	20 725
  Parameter	434	1 054
  Rint	0.036 5	0.084 8
  GOF on F 2	1.042	1.082
  R1, wR2 [I>2σ(I)]	0.023 6, 0.056 6	0.046 1, 0.108 9
  R1, wR2 (all data)	0.030 8, 0.060 9	0.068 7, 0.119 9

  下载: 导出CSV

  表 2  Gd^Ⅲ ion geometry analysis by SHAPE 2.0 for 1^*

  GdⅢ ion	D4d SAPR-8	D2d TDD-8	C2v JBTPR-8	C2v BTPR-8	D2d JSD-8
  Gd1	3.696	2.053	4.054	2.901	5.227
  * SAPR-8=square antiprism; TDD-8=triangular dodecahedron; JBTPR-8=biaugmented trigonal prism J50; BTPR-8=biaugmented trigonal prism; JSD-8=snub diphenoid J84.

  下载: 导出CSV

  表 3  Gd^Ⅲ ion geometry analysis by SHAPE 2.0 for 2^*

  GdⅢ ion	C4v JCSAPR-9	C4v CSAPR-9	D3h JTCTPR-9	D3h TCTPR-9	Cs MFF-9
  Gd1	1.93	1.301	3.129	1.611	1.588
  Gd2	2.165	1.492	3.521	1.824	1.604
  *JCSAPR-9=capped square antiprism J10; CSAPR-9=spherical capped square antiprism; JTCTPR-9=tricapped trigonal prism J51;TCTPR-9=spherical tricapped trigonal prism; MFF-9=muffin.

  下载: 导出CSV

  表 4  Comparison of -ΔS_m values for complexes 1, 2 and some reported Gd₂ complexes

  Dinuclear G(Ⅲ)-based complex	Mr	Magnetic interaction	-ΔSm/(J.K-l.kg-1)	ΔH/kOe	Ref.
  [Gd2(bfa)4(L)2].CH2Cl2a	1 747.16	AF (no J value reported)	18.5	70	[40]
  [Gd2(hfac)4(L)2]b	1 795.07	AF (J=-0.07 cm-1)	15.00	80	[41]
  [Gd(hfac)2(L)]2c	1 693.37	AF (J=-0.04 cm-1)	19.94	70	[42]
  [Gd2(dbm)4(L)2]d	1791.99	AF (no J value reported)	14.36	70	[43]
  [Gd2(hfac)4(L1)2]e	1 665.32	AF (J=-0.13 cm-1)	17.66	70	[44]
  [Gd2(hfac)4(L2)2]f	1 693.37	AF(J=-0.10cm-1)	14.81	70	[44]
  [Gd2(L1)2(tmhd)2(CH3O)2]g	1 670.21	AF (no J value reported)	18.59	70	[45]
  [Gd(bfa)2(L)]2h	1 681.61	AF (no J value reported)	17.78	70	[46]
  [Gd2(L)2(dbm)2(H2O)2]·CH3OHi	1 395.57	AF (J=-0.045 cm-1)	23.2	70	[47]
  [Gd2(dbm)2(L)2(CH3OH)2]j	1 445.76	AF (no J value reported)	21.1	70	[48]
  [Gd(OAc)3(H2O2]2-4H2O	2 474.95	F (J/kB=0.068(2) K)	40	70	[49]
  Complex 1	1 555.99	AF (no J value reported)	20.16	70	This work
  Complex 2	1 836.42	AF (no J value reported)	17.14	70	This work
  a HL=2-(((4-methylphenyl)imino)methyl)-8-hydroxyquinoline; b HL=2-((4-bromo-phenylimino)-methyl)-quinolin-8-ol; c HL=2-((4-ethylphenyl)imino)methyl-8-hydroxyquinoline; d HL=2-((4-nitrophenyl)imino)methyl-8-hydroxyquinoline; e HL1=2-(4-methylaniline-imino)methyl)-8-hydroxyquinoline; f HL2=2-((3, 4-dimethylaniline)-imino)methyl)-8-hydroxyquinoline; g HL1=bis-Schiff base ligand; h HL=2-(5-methyl-1, 2-oxazol-imino)methyl)-8-hydroxyquinoline; i HL=2-((1E)-(((pyridin-2-yl)formamido)imino)methyl)benzoic acid; j HL=N'-(4-(diethylamino)salicylaldehyde)pyridyl-2-carbohydrazide.

  下载: 导出CSV
•