Three Gd-based magnetic refrigerant materials with high magnetic entropy: From di-nuclearity to hexa-nuclearity to octa-nuclearity

Abstract

Magnetocaloric effect (MCE) is one of the most promising features of molecular-based magnetic materials. We reported three Gd-based magnetic refrigerant materials, namely, Gd₂(L)(NO₃)(H₂O)‧CH₃CN‧H₂O (1, H₂L = (Z)-N-[(1E)-(2-hydroxy-3-methphenyl)methylidene]pyrazine-2-carbohydrazonic acid), {Gd₆(L)₆(CO₃)₂(CH₃OH)₂(H₂O)₃Cl}Cl‧4CH₃CN (2), and Gd₈(L)₈(CO₃)₄(H₂O)₈‧2H₂O (3). Complex 1 contains two Gd^III ions linked by two η²:η¹:η¹:η¹:μ₂-L^2- ligands, which are seven-coordinated in a capped trigonal prism, and complex 2 possesses six Gd^III ions, contributing to a triangular prism configuration. For complex 3, eight Gd^III ions form a distorted cube arrangement. Moreover, the large values of magnetic entropy in the three complexes prove to be excellent candidates as cryogenic magnetic coolants.

Introduction

Ln-based complexes play a critical role in molecular-based materials not only due to the charming geometrical structures but also because of the extensive applications such as luminescence, catalysis, especially for magnetic materials including magnetocaloric effect (MCE) (Wu D et al., 2020; Shang et al., 2021; Wei et al., 2021), and single-molecule magnets (SMMs) (Liu et al., 2014; Liu et al., 2016; Zhang and Cheng, 2016; Reis, 2020). As a member of the Ln elements, the Gd ion is a perfect candidate in the synthesis of molecular-based magnetic refrigeration materials because of the large magnetothermal effects (Evangelisti et al., 2011; Chen et al., 2013; Chen et al., 2014; Wang et al., 2020a; Li et al., 2021; Lin et al., 2021; Wu T et al., 2021; Zhou et al., 2021). Some of the reported magnetic materials even possess a large cryogenic MCE, which is comparable to that of the commercial coolant {Gd₃Ga₅O₁₂} (Pecharsky and Gschneidner, 1997; Zhang S. et al., 2015; Zhang S.,-W. et al., 2015).

It is worth mentioning that in the pure 4f system, improving magnetic density is the ideal method to gain MCE performance (Zhang et al., 2016; Reis, 2020). Therefore, organic ligands play an important role in the building units of the complexes. In previous studies, various organic ligands (e. g. Schiff-based ligands (Aronica et al., 2006; Boulon et al., 2013; Mannini et al., 2014; Burgess et al., 2015; Nava et al., 2015; Wang et al., 2015; Lakma et al., 2019; Li et al., 2019; Wang et al., 2020b; Wang J. et al., 2021; Wang M. et al., 2021), carboxylates (Milios et al., 2007; Dermitzaki et al., 2015; Yin et al., 2015; Botezat et al., 2017; Feltham et al., 2017; Li et al., 2019; Zheng et al., 2020; Han et al., 2021; Zhou et al., 2021), diketones (Zhu et al., 2014; Yao et al., 2018; Wang et al., 2019a; Wang et al., 2019b; Shi et al., 2021), and diamines (Neves et al., 1992; Zhang et al., 2013; Cornia et al., 2014; Oyarzabal et al., 2014; Feltham et al., 2015; Luan et al., 2015; Lu et al., 2019) etc.) have been successfully utilized in the synthesis of MCE materials. Among them, Schiff-based ligands comprise rich O and N sites, which are widely used in the synthesis of many Ln complexes because of the simple synthesis and structural diversity.

In this work, three Gd-based magnetic refrigerant materials based on Schiff-based ligands (Z)-N-[(1E)-(2-hydroxy-3-methphenyl) methylidene]pyrazine-2-carbohydrazonic acid (H₂L) were synthesized, namely, Gd₂(L) (NO₃) (H₂O)‧CH₃CN‧H₂O (1), {Gd₆(L)₆(CO₃)₂(CH₃OH)₂(H₂O)₃Cl}Cl‧4CH₃CN (2), and Gd₈(L)₈(CO₃)₄(H₂O)₈‧2H₂O (3). Magnetic studies indicate that all complexes exhibit antiferromagnetic interactions between the spin centers and display large magnetic entropies.

Materials and methods

Materials

All reactions and manipulations were performed in the ambient atmosphere. The Schiff-based H₂L ligand was prepared by condensation with o-vanillin and hydrazine-2-carbohydrazide in methanol according to the literature (Chandrasekhar et al., 2013; Chen et al., 2016). Metal salts and other reagents were commercially available and used without further purification.

Synthesis

Synthesis of Gd₂(L)₂(NO₃)₂(H₂O)₂‧CH₃CN‧H₂O (1): a mixture of H₂L (0.1 mmol, 27.2 mg) and Gd(NO₃)₃·6H₂O (0.1 mmol, 45.7 mg) was dissolved in CH₃CN (5 ml) and CH₃OH (2.5 ml). After stirring for 5 min, pyridine (0.04 ml) was added and stirred for another 10 min. The solution was filtered and left to slowly evaporate. Well-shaped orange crystals were obtained after 1 week. Yield: 20 mg, 36% based on Gd. Elemental analysis (EA) calc. (%) for Gd₂C₃₀H₃₀N₁₂O₁₆, C: 31.91, H: 2.68, N: 14.89; found (%), C: 32.03, H: 2.61, N: 14.93.

{Gd₆(L)₆(CO₃)₂(CH₃OH)₂(H₂O)₃Cl}Cl‧4CH₃CN (2): a mixture of H₂L (0.2 mmol, 54.4 mg) and GdCl₃.6H₂O (0.2 mmol, 74.3 mg) was dissolved in CH₃CN (10 ml) and CH₃OH (5 ml). After stirring for 5 min, NaHCO₃ (0.2 mmol, 33.6 mg) was added and stirred for another 3 h. Well-shaped orange crystals were obtained after 1 week. Yield: 32 mg, 32% based on Gd. Elemental analysis (EA) calc. (%) for Gd₆C₉₀H₉₂N₂₈O₂₉Cl₂, C: 35.51, H: 3.05, N: 12.88; found (%), C: 35.72, H: 2.99, N: 12.92.

Gd₈(L)₈(CO₃)₄(H₂O)₈‧2H₂O (3): a mixture of H₂L (0.2 mmol, 13.6 mg) and GdCl₃.6H₂O (0.2 mmol, 18.6 mg) was dissolved in CH₃CN (5 ml) and CH₃OH (2.5 ml). After stirring for 5 min, NaCO₃ (0.2 mmol, 10.6 mg) was added and stirred for another 2 h. Well-shaped orange crystals were obtained after 1 week. Yield: 28 mg, 29% based on Gd. Elemental analysis (EA) calc. (%) for Gd₈C₁₀₈H₁₀₀N₃₂O₄₆, C: 33.78, H: 2.62, N: 11.67; found (%), C: 33.83, H: 2.51, N: 11.84.

Physical measurements

The C, H, and N elemental analyses were performed using an Elementar Vario-EL CHNS elemental analyzer. The Fourier transform-infrared (FT-IR) spectra were carried out from KBr pellets in the range 4,000–400 cm⁻¹ using an EQUINOX 55 spectrometer. Powder X-ray diffraction (PXRD) patterns were performed using the Bruker D8 Advance diffractometer (Cu–Kα, λ = 1.54056 Å). Magnetic susceptibility measurements were measured with a Quantum Design MPMS-XL7 SQUID. Polycrystalline samples were embedded in vaseline to prevent torquing. Data were corrected for the diamagnetic contribution calculated from Pascal constants.

Crystallographic study

Suitable single crystals for 1–3 were selected for single-crystal X-ray diffraction analysis. Data were collected using a Rigaku Oxford diffractometer with a Mo–Kα radiation (λ = 0.71073 Å) at 120 K. The structures were solved by direct methods and refined by least-squares on F² utilizing the SHELXTL program suite and Olex2 (Dolomanov et al., 2009; Sheldrick, 2015a,b). The hydrogen atoms were set in calculated positions and refined as riding atoms with common fixed isotropic thermal parameters. EA was used to detect the content of C, H, and N atoms. Detailed information about the crystal data and structure refinements is summarized in Table 1. Selected bond lengths and angles of complexes 1–3 are listed in Supplementary Table S1–S3.

Results and discussion

Description of the structures of 1–3

Complexes 1–3 are synthesized by the evolution method with H₂L and gadolinium salt in the solution of CH₃CN/CH₃OH (V₁:V₂ = 2:1) under the existence of alkali. The alkali is added to be conducive to protonate the ligand H₂L, which is beneficial to incorporate Gd^III ions. The H₂L ligand in all complexes is completely dehydrogenated adopting the μ₂:η²:η¹:η¹:η¹-mode (Scheme 1A), which is similar to the reported literature (Chandrasekhar et al., 2013; Chen et al., 2016; Zhang et al., 2017; Zhang  et al., 2016; Jiang et al., 2016).

SCHEME 1

Complex 1 is crystalized in the triclinic P-1 space group. As shown in Figure 1, the crystallography independent unit of 1 contains half of the molecule, including one Gd^III ion, one L₂^- ligand, one NO₃⁻ anion, and half of CH₃CN and H₂O molecules. The metallic Gd^III ions (Gd1 and Gd1A) are surrounded by two L₂^- ligands using the aforementioned mode, two NO₃⁻ anions and two H₂O molecules located above and below the plane, respectively. The average bond lengths of Gd-O and Gd-N are 2.379 (5) Å and 2.460 (5) Å (Supplementary Table S1), respectively, which are in accordance with those of the reported Gd-based complexes (Chen et al., 1995; Zhao et al., 2017; Mayans and Escuer, 2021; Ren et al., 2021). In complex 1, the Gd ion is seven-coordinated to form a capped trigonal prism, which is confirmed by CShM calculations (Alvarez et al., 2005; Casanova et al., 2005) (Supplementary Figure S1, Supplementary Table S4).

FIGURE 1

Complex 2 crystalizes in the same space group as complex 1, and the asymmetric unit comprises the whole molecule with six crystallographically independent Gd^III ions (Figure 2A). The six Gd ions are held together to form a {Gd₆} triangular prism metallic skeleton (Figure 2B). Therein, three Gd ions in the plane (Gd1, Gd2, and Gd3 or Gd4, Gd5, and Gd6) contribute a triangular configuration, which are bridged by one CO₃^2- anion in μ₃-η²:η²:η²-mode (Scheme 1B). The two triangular metallic skeletons are then linked together by six μ₂-O bridges from ligands.

FIGURE 2

All Gd ions are eight coordinated, showing two kinds of coordination geometry confirmed by CShM calculations (Alvarez et al., 2005; Casanova et al., 2005) (Supplementary Table S5). The Gd1, Gd2, Gd3, Gd5, and Gd6 ions are in {O₆N₂} environment with six O atoms and two N atoms from two chelated L^2- ligands, one CO₃^2- anion and one CH₃OH/H₂O molecule, which display a biaugmented trigonal prism configuration (Supplementary Figure S2). The average Gd-O and Gd-N distances are 2.352 (4) Å and 2.475 (4) Å, respectively (Supplementary Table S2), which are consistent with those reported Gd-based complexes (Chen et al., 1995; Zhao et al., 2017; Mayans and Escuer, 2021; Ren et al., 2021). However, Gd4 has triangular dodecahedron coordination geometry and is located in an {O₅N₂Cl} environment with five O and two N atoms from two chelated L^2- ligands and one Cl⁻ anion. The bond length of Gd4-Cl1 is 2.746 (1) Å, which is longer than that of Gd-O and Gd-N.

For complex 3, the synthetic method is the same as complex 2; except NaHCO₃ was used in place of Na₂CO₃. Surprisingly, complex 3 possesses an octa-nuclearity structure, which crystalizes in the triclinic P-1 space group. The asymmetric unit consists of a completed molecule, and there are eight crystallographically independent Gd atoms in the molecular structure (Figure 3A). As shown in Figure 3B, the eight Gd^III ions contribute to a cubic trapezoid metallic core. Gd1, Gd4, Gd5, and Gd8 ions lie in the four vertices of the plane below the cubic trapezoid, while Gd2, Gd3, Gd6, and Gd7 ions situate in the upper plane. The metallic core is held together by four CO₃^2- anions in μ₃-η²:η²:η¹-mode (Scheme 1C). The periphery of the metal core is ligated by eight L^2- ligands, eight H₂O molecules, and two lattice H₂O molecules.

FIGURE 3

There are two coordination numbers of Gd^III ions in complex 3 (Supplementary Figure S3). Gd1, Gd3, Gd5, and Gd7 are eight-coordinated ions in {O₆N₂} donor set from two L^2- ligands, two CO₃^2- anions, and one H₂O molecule, while Gd2, Gd4, Gd6, and Gd8 ions are nine-coordinated in the {O₇N₂} donor set. The difference between the two kinds of Gd ions is the diverse coordination modes of the CO₃^2- anion. There is only one coordination bond of O atom in CO₃^2- anion, which is adopted in Gd1, Gd3, Gd5, and Gd7 ions. For Gd2, Gd4, Gd6, and Gd8 ions, the bonding mode of the CO₃^2- anion is adopted in the bidentate mode. The eight metal ions exhibit three coordination geometries: biaugmented trigonal prism (Gd1), triangular dodecahedron (Gd3, Gd5, and Gd7), and muffin (Gd2, Gd4, Gd6, and Gd8) (Supplementary Tables S5,6). The average Gd-O distance is 2.361 (4) Å, which is shorter than that of Gd-N (2.564 (4) Å) lengths. The O/N-Gd-O/N angles are in the range of 60.99°–154.86°, which are in the normal range (Chen et al., 1995; Zhao et al., 2017; Mayans and Escuer, 2021; Ren et al., 2021).

It is worth mentioning that the use of different alkalis can affect the number of formed metal nuclearity. For the organic weak alkali triethylamine, which is used in complex 1, it only facilitates protonation of the ligand H₂L but is not involved in the final formation of complex 1. However, for complexes 2 and 3, the inorganic alkalis not only deprotonate the ligand but also participate in the construction of the molecules. Compared to NaHCO₃ in complex 2, the alkalinity of Na₂CO₃ is relatively strong. Moreover, mainly due to the degree of hydrolysis of carbonates being higher, there are more carbonate triangle skeletons in complex 3, making it easier to coordinate with Gd ions, thus forming an octa-nuclearity complex.

IR spectra and PXRD studies

The FT-IR spectra of complexes 1–3 were acquired (v = 4,000–500 cm⁻¹), which are shown in Supplementary Figure S4. Powder X-ray diffraction (PXRD) measurements for complexes 1–3 were performed for the crystalline crystals (Supplementary Figure S5), and the experimental patterns are in good agreement with the simulated ones from the crystallographic data. The minor inconsistencies in the intensity and shape of the peaks indicate the phase purity of complexes 1–3.

Magnetic studies

The direct current magnetic susceptibilities of complexes 1–3 were studied for polycrystalline samples in the temperature range of 2–300 K at an external magnetic field of 1000 Oe (Figure 4A). At room temperature, the χ_MT values of complexes 1–3 are 15.77, 47.16, and 62.81 cm³ K mol⁻¹, respectively, which is in good agreement with the expected spin-only values (Gd^III ion: 7.875 cm³ K mol⁻¹, g = 2). Upon cooling, the χ_MT values in all cases stay essentially unchanged until approximately 25 K and then followed by an obvious decrease to the minimum values of 13.29, 38.46, and 58.30 cm³ K mol⁻¹, indicating antiferromagnetic interactions (Kahn et al., 2000). Fitting the curve of χ_M⁻¹ vs. T with the Curie–Weiss Law (Figure 4B) gives the resulting C and θ values, which are listed in Supplementary Table S7. The negative θ values imply the presence of weak antiferromagnetic interaction within complexes 1–3.

FIGURE 4

The field dependence of the magnetization plots for complexes 1–3 was performed in the field range of 1–7 T at 2–8 K (Supplementary Figure S6). Magnetizations in all complexes are increased gradually at the entire field region, reaching saturation values of 13.81, 41.75, and 55.83 Nμ_B at 7 T and 2 K, respectively, close to the theoretical value (1: 14 Nμ_B; 2: 42 Nμ_B; 3: 56 Nμ_B). The reduced magnetization plots (M vs. HT⁻¹) in all complexes are superposable due to the isotropic system (Supplementary Figure S7).

Due to the complicated systems in complexes 2 and 3, only complex 1 is attempted to analyze the magnetic interactions by using a simplified spin Hamiltonian with the PHI program (Eq. 1):

The best-fit parameters are J = -0.022 (2) cm⁻¹ and g = 1.98 (Figure 4A; Supplementary Figure S8). The negative J value confirms the antiferromagnetic interactions between the Gd^III ions, which is in accordance with the trend of the χ_MT product with cooling and the result of the Curie–Weiss Law.

The isothermal magnetization for complexes 1–3 was measured from 2 to 8 K in an applied DC field up to 7 T to calculate the magnetic entropy (-∆S_m) according to the Maxwell equation (Pecharsky and Gschneidner, 1999) (Eq. 2). It can be seen that the curves of -∆S_m of complexes 1–3 gradually increase with decreasing temperature and increasing of magnetic field without saturation, the maximum -∆S_m values are 25.05 J kg⁻¹ K⁻¹, 27.21 J kg⁻¹ K⁻¹, and 30.79 J kg⁻¹ K⁻¹ at 2 K, ∆H = 7 T, respectively (Figure 5). These values are smaller than the theoretical values of 34.57 J kg⁻¹ K⁻¹ for 1, 34.07 J kg⁻¹ K⁻¹ for 2, and 36.01 J kg⁻¹ K⁻¹ for 3, which are calculated using Eq 3, (n = 2, 6, and 8 for 1, 2, and 3, respectively; S = 7/2 and the R value is 8.314 J mol⁻¹ K⁻¹), owing to the existence of antiferromagnetic coupling. The maximum -∆S_m of 1 in di-nuclearity complex is among the highest observed to date for 4f clusters appeared at low temperature (Table 2). Although complexes 2 and 3 do not possess the highest -∆S_m values, they are still comparable in the same nuclear complexes.

FIGURE 5

Conclusion

In conclusion, three clusters 1-{Gd₂}, 2-{Gd₆}, and 3-{Gd₈} based on Schiff ligand H₂L were synthesized. Complex 1 contains two Gd^III ions, and magnetic measurement indicates antiferromagnetic interactions between the metal core, which is also confirmed by PHI fitting. Complexes 2 and 3 are hexa-nuclearity with a biaugmented trigonal prism configuration and octa-nuclearity with a cubic trapezoid structure. Magnetic investigations indicate the antiferromagnetic interactions between Gd^III ions are observed in complexes 2 and 3. Magnetocaloric studies for complexes 1–3 show that the magnetic entropies of complexes 1–3 are smaller than the theoretical values, which is mainly caused by antiferromagnetic coupling. Furthermore, complex 1 exhibits a large magnetic entropy of 25.05 J kg⁻¹ K⁻¹ at 2.0 K in di-nuclearity magnetic refrigerant materials, while complexes 2 and 3 belong to the normal range in hexa-nuclearity and octa-nuclearity complexes, respectively, demonstrating that they are promising molecular magnetic coolants for low-temperature cooling applications.

References

• 1

  AdhikaryA.SheikhJ. A.BiswasS.KonarS. (2014). Synthesis, crystal structure and study of magnetocaloric effect and single molecular magnetic behaviour in discrete lanthanide complexes. Dalton Trans.43, 9334–9343. 10.1039/C4DT00540F

  • CrossRef
  • Google Scholar

• 2

  AlvarezS.AlemanyP.CasanovaD.CireraJ.LlunellM.AvnirD. (2005). Shape maps and polyhedral interconversion paths in transition metal chemistry. Coord. Chem. Rev.249, 1693–1708. 10.1016/j.ccr.2005.03.031

  • CrossRef
  • Google Scholar

• 3

  AronicaC.PiletG.ChastanetG.WernsdorferW.JacquotJ.-F.LuneauD. (2006). A nonanuclear dysprosium(III)–copper(II) complex exhibiting single‐molecule magnet behavior with very slow zero‐field relaxation. Angew. Chem. Int. Ed.45, 4659–4662. 10.1002/anie.200600513

  • CrossRef
  • Google Scholar

• 4

  BotezatO.van LeusenJ.KravtsovV. C.KogerlerP.BacaS. G. (2017). Ultralarge 3d/4f coordination wheels: From carboxylate/amino alcohol-supported {Fe₄Ln₂} to {Fe₁₈Ln₆} rings. Inorg. Chem.56, 1814–1822. 10.1021/acs.inorgchem.6b02100

  • CrossRef
  • Google Scholar

• 5

  BoulonM. E.CucinottaG.LuzonJ.Degl'InnocentiC.PerfettiM.BernotK.et al (2013). Magnetic anisotropy and spin-parity effect along the series of lanthanide complexes with DOTA. Angew. Chem. Int. Ed.52, 350–354. 10.1002/anie.201205938

  • CrossRef
  • Google Scholar

• 6

  BurgessJ. A.MalavoltiL.LanzilottoV.ManniniM.YanS.NinovaS.et al (2015). Magnetic fingerprint of individual Fe₄ molecular magnets under compression by a scanning tunnelling microscope. Nat. Commun.6, 8216–8222. 10.1038/ncomms9216

  • CrossRef
  • Google Scholar

• 7

  CasanovaD.LlunellM.AlemanyP.AlvarezS. (2005). The rich stereochemistry of eight-vertex polyhedra: A continuous shape measures study. Chem. Eur. J.11, 1479–1494. 10.1002/chem.200400799

  • CrossRef
  • Google Scholar

• 8

  ChandrasekharV.DasS.DeyA.HossainS.SutterJ.-P. (2013). Tetranuclear lanthanide (III) complexes containing dimeric subunits: Single-molecule magnet behavior for the Dy₄ analogue. Inorg. Chem.52, 11956–11965. 10.1021/ic401652f

  • CrossRef
  • Google Scholar

• 9

  ChenQ.MaF.MengY.-S.SunH.-L.ZhangY.-Q.GaoS. (2016). Assembling dysprosium dimer units into a novel chain featuring slow magnetic relaxation via formate linker. Inorg. Chem.55, 12904–12911. 10.1021/acs.inorgchem.6b02276

  • CrossRef
  • Google Scholar

• 10

  ChenX.-M.AubinS. M. J.WuY.-L.YangY.-S.MakT. C. W.HendricksonD. N. (1995). Polynuclear Cu^II₁₂M^III₆ (M = Y, Nd, or Gd) complexes encapsulating a ClO^4- anion: [Cu₁₂M₆(OH)₂₄(H₂O)₁₈(pyb)₁₂(ClO₄)](ClO₄)₁₇·nH₂O (pyb = pyridine betaine). J. Am. Chem. Soc.117, 9600–9601. 10.1021/ja00142a043

  • CrossRef
  • Google Scholar

• 11

  ChenY.-C.GuoF.-S.ZhengY.-Z.LiuJ.-L.LengJ.-D.TarasenkoR.et al (2013). Gadolinium(III)-hydroxy ladders trapped in succinate frameworks with optimized magnetocaloric effect. Chem. Eur. J.19, 13504–13510. 10.1002/chem.201301221

  • CrossRef
  • Google Scholar

• 12

  ChenY.-C.QinL.MengZ.-S.YangD.-F.WuC.FuZ.et al (2014). Study of a magnetic-cooling material Gd(OH)CO₃. J. Mat. Chem. A2, 9851–9858. 10.1039/C4TA01646G

  • CrossRef
  • Google Scholar

• 13

  CorniaA.RigamontiL.BoccediS.CleracR.RouzieresM.SoraceL. (2014). Magnetic blocking in extended metal atom chains: A pentachromium(II) complex behaving as a single-molecule magnet. Chem. Commun.50, 15191–15194. 10.1039/c4cc06693f

  • CrossRef
  • Google Scholar

• 14

  DermitzakiD.RaptopoulouC. P.PsycharisV.EscuerA.PerlepesS. P.StamatatosT. C. (2015). Nonemployed simple carboxylate ions in well-investigated areas of heterometallic carboxylate cluster chemistry: A new family of {Cu^II₄Ln^III₈} complexes bearing tert-butylacetate bridging ligands. Inorg. Chem.54, 7555–7561. 10.1021/acs.inorgchem.5b01179

  • CrossRef
  • Google Scholar

• 15

  DolomanovO. V.BourhisL. J.GildeaR. J.HowardJ. A. K.PuschmannH. (2009). OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr.42, 339–341. 10.1107/S0021889808042726

  • CrossRef
  • Google Scholar

• 16

  EvangelistiM.RoubeauO.PalaciosE.CamónA.HooperT. N.BrechinE. K.et al (2011). Cryogenic magnetocaloric effect in a ferromagnetic molecular dimer. Angew. Chem. Int. Ed.50, 6606–6609. 10.1002/anie.201102640

  • CrossRef
  • Google Scholar

• 17

  FelthamH. L. C.DhersS.RouzièresM.CléracR.PowellA. K.BrookerS. (2015). A family of fourteen soluble stable macrocyclic [NiIILnIII] heterometallic 3d–4f complexes. Inorg. Chem. Front.2, 982–990. 10.1039/c5qi00130g

  • CrossRef
  • Google Scholar

• 18

  FelthamH. L. C.DumasC.ManniniM.OteroE.SainctavitP.SessoliR.et al (2017). Proof of principle: Immobilisation of robust CuII 3 TbIII-macrocycles on small, suitably pre-functionalised gold nanoparticles. Chem. Eur. J.23, 2517–2521. 10.1002/chem.201604821

  • CrossRef
  • Google Scholar

• 19

  GuoF.-S.LengJ.-D.LiuJ.-L.MengZ.-S.TongM.-L. (2012). Polynuclear and polymeric gadolinium acetate derivatives with large magnetocaloric effect. Inorg. Chem.51, 405–413. 10.1021/ic2018314

  • CrossRef
  • Google Scholar

• 20

  HanL.-J.WangW.-M.WangX.-W.HuaiL.QiaoN.FangM. (2021). A rhombic shaped {GdIII2CoII2} heterometallic cluster exhibiting larger cryogenic magnetocaloric effect. Inorganica Chim. Acta514, 120020–120024. 10.1016/j.ica.2020.120020

  • CrossRef
  • Google Scholar

• 21

  HouY.-L.HanX.HuX.-Y.ShenJ.-X.WangJ.ShiY.et al (2020). Two LnIII4(LnIII = Gd and Dy) clusters constructed by 8-hydroxyquinoline schiff base and β-diketonate coligand: Magnetic refrigeration property and single-molecule magnet behavior. Inorganica Chim. Acta502, 119290–119303. 10.1016/j.ica.2019.119290

  • CrossRef
  • Google Scholar

• 22

  JiangY.BrunetG.HolmbergR. J.HabibF.KorobkovI.MurugesuM. (2016). Terminal solvent effects on the anisotropy barriers of Dy₂ systems. Dalton Trans.45, 16709–16715. 10.1039/C6DT03366K

  • CrossRef
  • Google Scholar

• 23

  KahnM. L.SutterJ.-P.GolhenS.GuionneauP.OuahabL.KahnO.et al (2000). Systematic investigation of the nature of the coupling between a ln(III) ion (ln = Ce(III) to Dy(III)) and its aminoxyl radical ligands. Structural and magnetic characteristics of a series of {Ln(organic radical)₂} compounds and the related {Ln(Nitrone)₂} derivatives. J. Am. Chem. Soc.122, 3413–3421. 10.1021/ja994175o

  • CrossRef
  • Google Scholar

• 24

  LakmaA.HossainS. M.van LeusenJ.KögerlerP.SinghA. K. (2019). Tetranuclear Mn^II, Co^II, Cu^II and Zn^II grid complexes of an unsymmetrical ditopic ligand: Synthesis, structure, redox and magnetic properties. Dalton Trans.48, 7766–7777. 10.1039/C9DT01041F

  • CrossRef
  • Google Scholar

• 25

  LiJ. N.LiN. F.WangJ. L.LiuX. M.PingQ. D.ZangT. T.et al (2021). A new family of boat-shaped Ln₈ clusters exhibiting the magnetocaloric effect and slow magnetic relaxation. Dalton Trans.50, 13925–13931. 10.1039/d1dt02390j

  • CrossRef
  • Google Scholar

• 26

  LiL.-F.KuangW.-W.LiY.-M.ZhuL.-L.XuY.YangP.-P. (2019). A series of new octanuclear Ln₈ clusters: Magnetic studies reveal a significant cryogenic magnetocaloric effect and slow magnetic relaxation. New J. Chem.43, 1617–1625. 10.1039/C8NJ04231D

  • CrossRef
  • Google Scholar

• 27

  LiL.YangL.-R.QiaoN.XueM.-M.FangZ.-X.RenJ.et al (2020). A novel tetranuclear Gd(III)-based cluster showing larger magnetic refrigeration property. J. Mol. Struct.1222, 128906–128911. 10.1016/j.molstruc.2020.128906

  • CrossRef
  • Google Scholar

• 28

  LinQ.-F.DingL.-L.XuZ.-H.WangQ.-q.LiN.-F.XuY.et al (2021). Three 3D Lanthanide coordination polymers: Synthesis, luminescence and magnetic properties. J. Mol. Struct.1234, 130167–130173. 10.1016/j.molstruc.2021.130167

  • CrossRef
  • Google Scholar

• 29

  LiuC.-M.HaoX. (2022). Asymmetric assembly of chiral lanthanide(III) tetranuclear cluster complexes using achiral mixed ligands: Single-molecule magnet behavior and magnetic entropy change. ACS Omega7, 20229–20236. 10.1021/acsomega.2c02155

  • CrossRef
  • Google Scholar

• 30

  LiuJ.-L.ChenY.-C.GuoF.-S.TongM.-L. (2014). Recent advances in the design of magnetic molecules for use as cryogenic magnetic coolants. Coord. Chem. Rev.281, 26–49. 10.1016/j.ccr.2014.08.013

  • CrossRef
  • Google Scholar

• 31

  LiuJ.-L.ChenY.-C.TongM.-L. (2016). Molecular design for cryogenic magnetic coolants. Chem. Rec.16, 825–834. 10.1002/tcr.201500278

  • CrossRef
  • Google Scholar

• 32

  LuG.WangJ.ZhangC.-J.BalaS.ChenY.-C.HuangG.-Z.et al (2019). Single-ion magnet and luminescent properties in a Dy(III) triangular dodecahedral complex. Inorg. Chem. Commun.102, 16–19. 10.1016/j.inoche.2019.02.003

  • CrossRef
  • Google Scholar

• 33

  LuanF.LiuT.YanP.ZouX.LiY.LiG. (2015). Single-molecule magnet of a tetranuclear dysprosium complex disturbed by a salen-type ligand and chloride counterions. Inorg. Chem.54, 3485–3490. 10.1021/acs.inorgchem.5b00061

  • CrossRef
  • Google Scholar

• 34

  ManniniM.BertaniF.TudiscoC.MalavoltiL.PogginiL.MisztalK.et al (2014). Magnetic behaviour of TbPc₂ single-molecule magnets chemically grafted on silicon surface. Nat. Commun.5, 4582–4589. 10.1038/ncomms5582

  • CrossRef
  • Google Scholar

• 35

  MayansJ.EscuerA. (2021). Correlating the axial zero field splitting with the slow magnetic relaxation in Gd^III SIMs. Chem. Commun.57, 721–724. 10.1039/D0CC07474H

  • CrossRef
  • Google Scholar

• 36

  MiliosC. J.InglisR.VinslavaA.BagaiR.WernsdorferW.ParsonsS.et al (2007). Toward a magnetostructural correlation for a family of Mn₆ SMMs. J. Am. Chem. Soc.129, 12505–12511. 10.1021/ja0736616

  • CrossRef
  • Google Scholar

• 37

  NavaA.RigamontiL.ZangrandoE.SessoliR.WernsdorferW.CorniaA. (2015). Redox-controlled exchange bias in a supramolecular chain of Fe₄ single-molecule magnets. Angew. Chem. Int. Ed.54, 8777–8782. 10.1002/anie.201500897

  • CrossRef
  • Google Scholar

• 38

  NevesA.ErthalS. M. D.VencatoI.CeccatoA. S.MascarenhasY. P.NascimentoO. R.et al (1992). Synthesis, crystal structure, electrochemical, and spectroelectrochemical properties of the new manganese(III) complex [Mn^III(BBPEN)] [PF₆] [H₂BBPEN = N, N'-bis(2-hydroxybenzyl)-N, N'-bis(2-methylpyridyl)ethylenediamine]. Inorg. Chem.31, 4749–4755. 10.1021/ic00049a008

  • CrossRef
  • Google Scholar

• 39

  OyarzabalI.RuizJ.SecoJ. M.EvangelistiM.CamonA.RuizE.et al (2014). Rational electrostatic design of easy-axis magnetic anisotropy in a Zn(II)-Dy(III)-Zn(II) single-molecule magnet with a high energy barrier. Chem. Eur. J.20, 14262–14269. 10.1002/chem.201403670

  • CrossRef
  • Google Scholar

• 40

  PecharskyV. K.GschneidnerJ. K. A. (1997). Giant magnetocaloric effect in Gd₅{Si₂Ge₂. Phys. Rev. Lett.78, 4494–4497. 10.1103/PhysRevLett.78.4494

  • CrossRef
  • Google Scholar

• 41

  PecharskyV. K.GschneidnerK. A.Jr (1999). Magnetocaloric effect and magnetic refrigeration. J. Magn. Magn. Mat.200, 44–56. 10.1016/S0304-8853(99)00397-2

  • CrossRef
  • Google Scholar

• 42

  ReisM. S. (2020). Magnetocaloric and barocaloric effects of metal complexes for solid state cooling: Review, trends and perspectives. Coord. Chem. Rev.417, 213357. 10.1016/j.ccr.2020.213357

  • CrossRef
  • Google Scholar

• 43

  RenJ.WeiX. Q.XuR. S.ChenZ. Y.WangJ.WangM.et al (2021). A potential ferromagnetic lanthanide‒transition heterometallic molecular‒based bacteriostatic agent. J. Mol. Struct.1229, 129783. 10.1016/j.molstruc.2020.129783

  • CrossRef
  • Google Scholar

• 44

  ShangY.CaoY.XieY.ZhangS.ChengP. (2021). A 1D Mn-based coordination polymer with significant magnetocaloric effect. Polyhedron202, 115173–115179. 10.1016/j.poly.2021.115173

  • CrossRef
  • Google Scholar

• 45

  SheldrickG. M. (2015a). Crystal structure refinement with SHELXL. Acta Crystallogr. C Struct. Chem.C71, 3–8. 10.1107/S2053229614024218

  • CrossRef
  • Google Scholar

• 46

  SheldrickG. M. (2015b). Shelxt - integrated space-group and crystal-structure determination. Acta Crystallogr. A Found. Adv.A71, 3–8. 10.1107/S2053273314026370

  • CrossRef
  • Google Scholar

• 47

  ShenH.-Y.WangW.-M.BiY.-X.GaoH.-L.LiuS.CuiJ.-Z. (2015). Luminescence, magnetocaloric effect and single-molecule magnet behavior in lanthanide complexes based on a tridentate ligand derived from 8-hydroxyquinoline. Dalton Trans.44, 18893–18901. 10.1039/c5dt02894a

  • CrossRef
  • Google Scholar

• 48

  ShiQ.-H.XueC.-L.FanC.-J.YanL.-L.QiaoN.FangM.et al (2021). Magnetic refrigeration property and slow magnetic relaxation behavior of five dinuclear Ln(III)-based compounds. Polyhedron194, 114938. 10.1016/j.poly.2020.114938

  • CrossRef
  • Google Scholar

• 49

  ShiX.-H.HaoS.-S.WangM.-J.ZhangL.LiangW.-H.GaoH.-M.et al (2020). Two Ln(III)₂ (Ln = Gd and Dy) compounds showing magnetic refrigeration and slow magnetic relaxation. J. Mol. Struct.1210, 127997. 10.1016/j.molstruc.2020.127997

  • CrossRef
  • Google Scholar

• 50

  WangJ.WuZ.-L.YangL.-R.XueM.-M.FangZ.-X.LuoS.-C.et al (2021a). Two lanthanide-based dinuclear clusters (Gd₂ and Dy₂) with schiff base derivatives: Synthesis, structures and magnetic properties. Inorganica Chim. Acta514, 120015. 10.1016/j.ica.2020.120015

  • CrossRef
  • Google Scholar

• 51

  WangM.LuL.SongW.WangX.SunT.ZhuJ.et al (2021b). AIE-active Schiff base compounds as fluorescent probe for the highly sensitive and selective detection of Al³⁺ ions. J. Lumin.233, 117911. 10.1016/j.jlumin.2021.117911

  • CrossRef
  • Google Scholar

• 52

  WangW.-M.GaoY.YueR.-X.QiaoN.WangD.-T.ShiY.et al (2020c). Construction of a family of Ln₃ clusters using multidentate schiff base and β-diketonate ligands: Fluorescence properties, magnetocaloric effect and slow magnetic relaxation. New J. Chem.44, 9230–9237. 10.1039/d0nj01172j

  • CrossRef
  • Google Scholar

• 53

  WangW.-M.HeL.-Y.WangX.-X.ShiY.WuZ.-L.CuiJ.-Z. (2019b). Linear-shaped LnIII 4 and LnIII 6 clusters constructed by a polydentate schiff base ligand and a β-diketone co-ligand: Structures, fluorescence properties, magnetic refrigeration and single-molecule magnet behavior. Dalton Trans.48, 16744–16755. 10.1039/c9dt03478a

  • CrossRef
  • Google Scholar

• 54

  WangW.-M.HuaiL.WangX.-W.JiangK.-J.ShenH.-Y.GaoH.-L.et al (2020d). Structures, magnetic refrigeration and single molecule-magnet behavior of five rhombus-shaped tetranuclear Ln(III)-based clusters. New J. Chem.44, 10266–10274. 10.1039/d0nj01969k

  • CrossRef
  • Google Scholar

• 55

  WangW.-M.WangM.-J.HaoS.-S.ShenQ.-Y.WangM.-L.LiuQ.-L.et al (2020a). ‘Windmill’-shaped LnIII 4 (LnIII = Gd and Dy) clusters: Magnetocaloric effect and single-molecule-magnet behavior. New J. Chem.44, 4631–4638. 10.1039/c9nj05317d

  • CrossRef
  • Google Scholar

• 56

  WangW.-M.XueC.-L.JingR.-Y.MaX.YangL.-N.LuoS.-C.et al (2020b). Two hexanuclear lanthanide Ln₆^III clusters featuring remarkable magnetocaloric effect and slow magnetic relaxation behavior. New J. Chem.44, 18025–18030. 10.1039/D0NJ03442H

  • CrossRef
  • Google Scholar

• 57

  WangW.-M.YueR.-X.GaoY.WangM.-J.HaoS.-S.ShiY.et al (2019a). Large magnetocaloric effect and remarkable single-molecule-magnet behavior in triangle-assembled LnIII 6 clusters. New J. Chem.43, 16639–16646. 10.1039/C9NJ03921J

  • CrossRef
  • Google Scholar

• 58

  WangW.-M.ZhangH.-X.WangS.-Y.ShenH.-Y.GaoH.-L.CuiJ.-Z.et al (2015). Ligand field affected single-molecule magnet behavior of lanthanide(III) dinuclear complexes with an 8-hydroxyquinoline Schiff base derivative as bridging ligand. Inorg. Chem.54, 10610–10622. 10.1021/acs.inorgchem.5b01404

  • CrossRef
  • Google Scholar

• 59

  WangY. -X.XuQ.RenP.ShiW.ChengP. (2019c). Solvent-induced formation of two gadolinium clusters demonstrating strong magnetocaloric effects and ferroelectric properties. Dalton Trans.48, 2228–2233. 10.1039/c8dt04267e

  • CrossRef
  • Google Scholar

• 60

  WeiW.WangX.ZhangK.TianC.-B.DuS.-W. (2019). Tuning the topology from fcu to pcu: Synthesis and magnetocaloric effect of metal–organic frameworks based on a hexanuclear Gd(III)-hydroxy cluster. Cryst. Growth Des.19, 55–59. 10.1021/acs.cgd.8b01566

  • CrossRef
  • Google Scholar

• 61

  WeiW.XieR.-K.DuS.-W.TianC.-B.ChaiG.-L. (2021). Synthesis, structure, magnetocaloric effect and DFT calculations of a Mn^II cluster-based inorganic coordination polymer. J. Alloys Compd.878, 160353–160361. 10.1016/j.jallcom.2021.160353

  • CrossRef
  • Google Scholar

• 62

  WuD. Q.ZhangM. L.LiZ. Y.ZhangP. P.ZhangM. Y.WuC. F.et al (2021). A two dimensional Gd^III coordination polymer based on isonicotinic acid N‐oxide with large magnetocaloric effect. Z. Anorg. Allg. Chem.647, 1542–1546. 10.1002/zaac.202100033

  • CrossRef
  • Google Scholar

• 63

  WuT. X.TaoY.HeQ. J.LiH. Y.BianH. D.HuangF. P. (2021). Constructing an unprecedented {MnII 38} matryoshka doll with a [Mn 18(CO3 ) 9] inorganic core and magnetocaloric effect. Chem. Commun.57, 2732–2735. 10.1039/d0cc07884k

  • CrossRef
  • Google Scholar

• 64

  XuC.WuZ.FanC.YanL.WangW.JiB. (2021). Synthesis of two lanthanide clusters LnIII 4 (Gd 4 and Dy 4) with [2×2] square grid shape: Magnetocaloric effect and slow magnetic relaxation behaviors. J. Rare Earths39, 1082–1088. 10.1016/j.jre.2020.08.015

  • CrossRef
  • Google Scholar

• 65

  YaoX.YanP.AnG.LiY.LiW.LiG. (2018). Investigation of magneto-structural correlation based on a series of seven-coordinated beta-diketone Dy(iii) single-ion magnets with C_2v and C_3v local symmetry. Dalton Trans.47, 3976–3984. 10.1039/c7dt04764a

  • CrossRef
  • Google Scholar

• 66

  YinD.-D.ChenQ.MengY.-S.SunH.-L.ZhangY.-Q.GaoS. (2015). Slow magnetic relaxation in a novel carboxylate/oxalate/hydroxyl bridged dysprosium layer. Chem. Sci.6, 3095–3101. 10.1039/c5sc00491h

  • CrossRef
  • Google Scholar

• 67

  ZhangL.JungJ.ZhangP.GuoM.ZhaoL.TangJ.et al (2016). Site-resolved two-step relaxation process in an asymmetric Dy₂ single-molecule magnet. Chem. Eur. J.22, 1392–1398. 10.1002/chem.201503422

  • CrossRef
  • Google Scholar

• 68

  ZhangL.ZhangY.-Q.ZhangP.ZhaoL.GuoM.TangJ. (2017). Single-molecule magnet behavior enhanced by synergic effect of single-ion anisotropy and magnetic interactions. Inorg. Chem.56, 7882–7889. 10.1021/acs.inorgchem.7b00625

  • CrossRef
  • Google Scholar

• 69

  ZhangP.ZhangL.LinS.-Y.TangJ. (2013). Tetranuclear [MDy]₂ compounds and their dinuclear [MDy] (M = Zn/Cu) building units: Their assembly, structures, and magnetic properties. Inorg. Chem.52, 6595–6602. 10.1021/ic400620j

  • CrossRef
  • Google Scholar

• 70

  ZhangS., -W.DuanE.ChengP. (2015b). An exceptionally stable 3D GdIII-organic framework for use as a magnetocaloric refrigerant. J. Mat. Chem. A Mat.3, 7157–7162. 10.1039/c4ta06209d

  • CrossRef
  • Google Scholar

• 71

  ZhangS.ChengP. (2016). Coordination-cluster-based molecular magnetic refrigerants. Chem. Rec.16, 2077–2126. 10.1002/tcr.201600038

  • CrossRef
  • Google Scholar

• 72

  ZhangS.DuanE.HanZ.LiL.ChengP., (2015a). Lanthanide coordination polymers with 4, 4'-azobenzoic acid: Enhanced stability and magnetocaloric effect by removing guest solvents. Inorg. Chem.54, 6498–6503. 10.1021/acs.inorgchem.5b00797

  • CrossRef
  • Google Scholar

• 73

  ZhaoX. Q.WangJ.BaoD. X.XiangS.LiuY. J.LiY. C. (2017). The ferromagnetic [Ln₂Co₆] heterometallic complexes. Dalton Trans.46, 2196–2203. 10.1039/c6dt04375e

  • CrossRef
  • Google Scholar

• 74

  ZhengT.-F.TianX.-M.JiJ.LuoH.YaoS.-L.LiuS.-J.et al (2020). Two Gd₂ cluster complexes with monocarboxylate ligands displaying significant magnetic entropy changes. J. Mol. Struct.1200, 127094. 10.1016/j.molstruc.2019.127094

  • CrossRef
  • Google Scholar

• 75

  ZhouM.WuL.-H.WuX.-Y.YaoS.-L.ZhengT.-F.XieX.et al (2021). Two dinuclear Gd^III clusters based on isobutyric acid and nicotinic acid with large magnetocaloric effects. J. Mol. Struct.1227, 129689. 10.1016/j.molstruc.2020.129689

  • CrossRef
  • Google Scholar

• 76

  ZhuJ.WangC.LuanF.LiuT.YanP.LiG. (2014). Local coordination geometry perturbed beta-diketone dysprosium single-ion magnets. Inorg. Chem.53, 8895–8901. 10.1021/ic500501r

  • CrossRef
  • Google Scholar