{Gd₄₄Ni₂₂}: a gigantic 3d–4f wheel-like nanoscale cluster with a large magnetocaloric effect

Abstract

Multinuclear 3d–4f nano-clusters, consisting of a large number of metal ions, are interesting both structurally and functionally. The Gd(III) containing clusters, in particular, attract great research attention because of their significant magnetocaloric effect. Here, we report the synthesis of a gigantic 3d–4f wheel-like cluster, {Gd₄₄Ni₂₂}, achieved through self-assembly using a “mixed-ligand” strategy. Magnetic characterization reveals that the {Gd₄₄Ni₂₂} cluster exhibits a large magnetocaloric effect (MCE), with an isothermal magnetic entropy change of 44.9 J kg⁻¹ K⁻¹ at 2.0 K for ΔH = 7 T, which is one of the largest among all of the high-nuclearity Ni–Gd clusters.

---

Introduction

High-nuclearity 3d–4f metal oxide/hydroxide clusters (M > 25) have attracted extensive research attention because of their fascinating structures and interesting properties.^1–10 Among the different properties, a particularly interesting one is the molecular magnetocaloric effect (MCE).^11–15 The MCE is a phenomenon that leads to a reversible temperature change when a material is exposed to a changing magnetic field.¹⁶ The MCE is safe (without producing greenhouse gases), quiet, cheap, highly durable, and highly efficient (i.e. it requires only a small number of moving parts).¹⁷ Currently, the greatest emphasis in the commercial use of MCE is on room temperature cooling (e.g. air conditioning, freezers, etc.). However, the cryogenic application of magnetic cooling materials will be increasingly important with the development of quantum computers, which require ultra-low temperatures.^18,19 As a class of highly efficient refrigerants at cryogenic temperatures, molecular magnets are promising materials which exhibit a large MCE.^20,21

Research reveals that metal oxide/hydroxide clusters displaying large MCEs share certain structural and functional features. These features include the high-spin ground state, large metal/ligand mass ratio (to ensure a high magnetic density), low-lying excited spin states, negligible magnetic anisotropy, and weak magnetic exchange coupling. Following this logic, research efforts on improving the MCE can be roughly divided into three categories. In the first category, 3d-clusters (e.g. {Fe₁₂} and {Mn₈}),^22–24 with high ground-state spin values, have been studied. However, strong magnetic coupling between transition metal ions results in antiferromagnetic interactions, leading to small MCEs. In the second category, studies have demonstrated larger MCEs in high-nuclearity Gd(III) oxide/hydroxide clusters. This is attributed to the Gd(III) ions with f⁷ electron configuration, affording multiple low-lying excited spin states and a possible ground state with a large spin value.²⁵ For example, high-nuclearity Gd oxide/hydroxide clusters with large MCEs have been reported recently, including {Gd₆₀} (with the maximum magnetic entropy change (−ΔS_m) of 48.0 J kg⁻¹ K⁻¹),¹² {Gd₁₀₄} (−ΔS_m = 46.9 J kg⁻¹ K⁻¹),²⁶ {Gd₄₈} (−ΔS_m = 43.6 J kg⁻¹ K⁻¹),²⁷etc. Finally, in the third category, Gd(III) ions have been exploited to mitigate the strong magnetic coupling between transition metal ions. By combining 3d metal ions and Gd(III), heterometallic 3d-Gd(III) clusters with small ligands turn out to be most promising for achieving a large MCE.¹⁵ Heterometallic 3d-Gd(III) clusters with large MCEs have been reported in recent years, such as {Gd₁₀₂Ni₃₆} (−ΔS_m = 41.3 J kg⁻¹ K⁻¹),²⁸ {Gd₉₆Ni₆₄} (−ΔS_m = 42.8 J kg⁻¹ K⁻¹),²⁹ {Gd₇₈Ni₆₄} (−ΔS_m = 40.6 J kg⁻¹ K⁻¹),³⁰etc. Among different 3d-Gd(III) clusters, wheel-like clusters are less observed. To date, the only reported 3d-Gd wheel-like structures are {Gd₂₄Cu₃₆}³¹ and {Gd₂₄Co₁₆},³² both with small −ΔS_m of 21.0 J kg⁻¹ K⁻¹ and 26.0 J kg⁻¹ K⁻¹, respectively. It is therefore important to obtain new heterometallic 3d-Gd(III) wheel-like clusters exhibiting a large MCE, to explore the relationship between the cluster structure and magnetocaloric effects.

In this work, a new wheel-like 3d-Gd(III) oxide/hydroxide cluster {Gd₄₄Ni₂₂} (1), with the formula [Gd₄₄Ni₂₂(CO₃)₁₆(NO₃)₄(H₂O)₅₈(μ₃-OH)₇₆(μ₂-OH)₆(IDA)₂₈(H₂dmpa)₂]·(H₂O)_x (1, x ≈ 118) (H₂dmp = 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid, IDA = iminodiacetic acid), is synthesized by using “mixed-ligands” to control the hydrolysis of Gd(III) and Ni(II) ions. The cluster structure and magnetic properties of 1 are investigated in detail to study the structure–property relationship to the magnetocaloric effects.

Results and discussion

Single crystals of the {Gd₄₄Ni₂₂} clusters (Fig. S1†) are obtained through the hydrolysis of Gd(NO₃)₃·6H₂O and Ni(NO₃)₂·6H₂O in the presence of mixed ligands {i.e., iminodiacetic acid (IDA) and 2,2-dimethylol propionic acid (H₃dmpa)}. Single-crystal X-ray diffraction (Tables S1–S3†) reveals that {Gd₄₄Ni₂₂} crystallizes in the monoclinic space group P2₁/n, with the formula [Gd₄₄Ni₂₂(CO₃)₁₆(NO₃)₄(H₂O)₅₈(μ₃-OH)₇₆(μ₂-O)₆(IDA)₂₈(H₂dmpa)₂]·(H₂O)_x (1, x ≈ 118). The {Gd₄₄Ni₂₂} cluster features a novel giant wheel-like structure with an outer diameter of ∼2.8 nm. The {Gd₄₄Ni₂₂} wheel also possesses an inner cavity, with the dimensions of 0.8 nm and 1.9 nm, respectively, in two perpendicular directions (Fig. 1).

Fig. 1 (a) The structure of wheel-like {Gd₄₄Ni₂₂} cluster; (b) structure of the wheel-like geometry of {Gd₄₄Ni₂₂} consisting of 44 gadolinium and 22 nickel ions; polyhedron representation of the {Gd₄₄Ni₂₂} cluster (c) and (d). Color code: purple, Gd; green, Ni; red, O; gray, C; white, H.

By taking a close look, we find that {Gd₄₄Ni₂₂} consists of one wheel-shaped {Gd₄₂Ni₂₂} unit (connected by μ₃-OH, CO₃²⁻ and IDA ligands) and two Gd³⁺ ions (coordinated by NO₃⁻ and H₃dmpa ligands). In the structure, the trivalent cations Gd³⁺ are eight-fold or nine-fold coordinated with O and N atoms, resulting in the [GdO₉], [GdO₈N], and [GdO₈] polyhedra (Fig. S2a, 5b, and 5c†). The Ni²⁺ ions are all six-coordinated with O and N atoms to form distorted [NiO₅N] octahedra (Fig. S2d†). The long distance between two neighboring metal ions (Gd⋯Gd = 3.618–3.971 Å and Gd⋯Ni = 3.452–3.538 Å) likely limits their magnetic interactions.

The wheel-shaped {Gd₄₂Ni₂₂} unit (Fig. 2a) consists of three different types of cluster subunits (I, II, and III). Subunit type I, formulated as [Gd₇(μ₃-OH)₈] (Fig. 2b), can be viewed as two cubane-like [Gd₄(μ₃-OH)₄] units that share a common Gd³⁺ vertex. Type II, formulated as [Gd₁₀Ni₇(μ₃-OH)₁₂(CO₃)₂] ({Gd₁₀Ni₇}), can be viewed as two CO₃²⁻ templated five-member rings sharing a Gd³⁺ vertex while bridged by one additional Gd³⁺ ion (Fig. 2c). Here, CO₃²⁻ likely originates from the absorption of atmospheric CO₂ by the reaction mixture, as observed by other researchers.^12,33 In addition, besides the CO₃²⁻ ligands, the ten Gd³⁺ ions in each {Gd₁₀Ni₇} unit are connected by twelve hydroxo ligands, with seven Ni²⁺ ions distributed on the outer edge and connected to Gd³⁺ ions by μ₃-OH. Finally, subunit type III can be described as [Gd₂Ni₂(μ₃-OH)₂(CO₃)₂], with two Gd²⁺ and two Ni²⁺ connected by two μ₃-OH and two CO₃²⁻ ligands (Fig. 2d). Two type I subunits, two type II subunits, and four type III subunits are joined together by sixteen CO₃²⁻, eighty μ₃-OH, and two μ₂-O groups, forming the wheel-shaped {Gd₄₂Ni₂₂} component.

Fig. 2 Ball-and-stick views of the assembly unit of the {Gd₄₄Ni₂₂} cluster. (a) {Gd₄₂Ni₂₂} units; (b) type I ([Gd₇(μ₃-OH)₈] unit); (c) type II ([Gd₁₀Ni₇(μ₃-OH)₁₂(CO₃)₂] unit); (d) type III ([Gd₂Ni₂(μ₃-OH)₂(CO₃)₂] unit).

In the structure of {Gd₄₄Ni₂₂}, IDA and H₃dmpa have two functions: one is to link the type I, type II, and type III subunits via coordination interactions and the other is to stabilize the wheel-shaped {Gd₄₄Ni₂₂} core. The IDA²⁻ ligand coordinates to the Gd³⁺ and Ni²⁺ ions are of three types. The first type coordinates to two Gd³⁺ ions and three Ni²⁺ ions in a μ₅-η_Gd¹(O):η_Gd¹(O):η_Ni¹(O):η_Ni³(O,N,O):η_Ni¹(O) mode (Fig. 3a). The second type coordinates to three Gd³⁺ ions and two Ni²⁺ ions in a μ₅-η_Gd¹(O):η_Gd¹(O):η_Gd¹(O):η_Ni³(O,N,O):η_Ni¹(O) mode (Fig. 3b). The third type coordinates to three Gd³⁺ ions and two Ni²⁺ ions in a μ₅-η_Gd¹(O):η_Gd¹(O):η_Gd³(O,N,O):η_Gd¹(O):η_Ni¹(O) mode (Fig. 3c). Meanwhile, the H₃dmpa ligand coordinates to one Gd³⁺ and one Ni²⁺ in a μ₂-η_Gd³(O,O,O):η_Ni¹(O) mode (Fig. 3d). Structurally, the IDA ligand plays a key role in the formation of a wheel-shaped {Gd₄₂Ni₂₂} unit. Two additional Gd³⁺ ions attach to the {Gd₄₂Ni₂₂} unit only through H₃dmpa ligands, leading to the final {Gd₄₄Ni₂₂} wheel. Interestingly, the packing of {Gd₄₄Ni₂₂} clusters within the lattice results in a nanotube with a one-dimensional channel along the a-axis (Fig. S3†).

Fig. 3 Coordination modes of the IDA ligand (a–c); coordination mode of the H₃ dmpa ligand.

It is worth pointing out that high-nuclearity 3d–4f wheel-shaped nanoscale clusters with a large central opening are still underdeveloped. As far as we know, only {Cu^II₃₆Ln^III₂₄} (Ln = Dy and Gd)³¹ and {Co^II₁₆Ln^III₂₄} (Ln = Dy and Gd)³² clusters have been reported. {Cu^II₃₆Ln^III₂₄} (Ln = Dy and Gd) consists of two alternating subunits (i.e. cubane-like [Ln₄(OH)₄] and boat-shaped [Cu₆(OH)₈(NO₃)]). The {Cu^II₃₆Ln^III₂₄} wheel exhibits a diagonal dimension of ∼4.6 nm, a thickness of about ∼1.8 nm, and a central opening with a diameter of ∼0.8 nm. Benzoate is involved in the formation of {Cu^II₃₆Ln^III₂₄}, as the primary linker and the protective ligand. Other wheel-shaped clusters, {Co^II₁₆Ln^III₂₄} (Ln = Dy and Gd), have been successfully synthesized by adopting pyridyl-functionalized β-diketone as the ligand. The metallo-core of {Co₁₆Ln₂₄} is constructed by a super-square {Ln₂₄} with an octagonal prism {Co₁₆}. The diameter and thickness of the {Co^II₁₆Ln^III₂₄} cluster are 3.0 nm and 2.0 nm, respectively. Clearly, the {Gd^III₄₄Ni^II₂₂} cluster reported in this work represents a new type of high-nuclearity wheel-shaped cluster, with more metal atoms (44 gadolinium and 22 nickel atoms) than those in the previous examples.

The temperature dependence of direct-current (dc) magnetic susceptibility is characterized on {Gd₄₄Ni₂₂} in an applied magnetic field of 1000 Oe and in the temperature range 2–300 K. The characterization was performed on the polycrystalline powder samples (Fig. S4–S6†). As shown in Fig. S7,† the observed χ_mT value of 365.9 cm³ K mol⁻¹ (at 300 K) is slightly smaller than the theoretical value of 373.2 cm³ K mol⁻¹ calculated using the Lande formula^34,35 based on 22 uncorrelated Ni²⁺ ions (26.6 cm³ K mol⁻¹ for S = 1 and g = 2.2) and 44 uncorrelated Gd³⁺ ions (346.7 cm³ K mol⁻¹ for S = 7/2 and g = 2). This result confirms the limited interaction between these metal cations. The data over the temperature range of 2–300 K fit the Curie–Weiss law well, resulting in C = 362.3 cm³ K mol⁻¹ and θ = −5.3 K for the {Gd₄₄Ni₂₂} cluster. The negative θ further confirms the presence of weak antiferromagnetic interactions. This behavior might be ascribed to the weak exchange interactions between the metal ions (Ni⋯Ni, Ni⋯Gd, and Gd⋯Gd) via the bridging ligands.

The generally weak magnetic coupling between Gd³⁺ and 3d transition metal ions, benefiting from the ability of Gd³⁺ to mitigate the otherwise strong 3d–3d magnetic exchange, makes the 3d-Gd(III) clusters a valid class of materials for magnetic cooling applications. Here, the presence of a large number of Gd(III) ions in {Gd₄₄Ni₂₂} prompts us to investigate its magnetocaloric effect in the context of developing molecular materials for magnetic cooling.^36,37 The field (H) dependence of the magnetization (M) of {Gd₄₄Ni₂₂} at low temperature (2–10 K) is measured (Fig. 4a and Fig. S8†). The M vs. H data show a steady increase in magnetization, reaching 298.3Nμ_B (N is the Avogadro constant and μ_B is the Bohr magneton) under 7 T at 2 K without achieving saturation (Fig. S8†). This value is slightly lower than the expected value for 66 uncorrelated metal ions (cal. 317.5Nμ_B). This again confirms the weak antiferromagnetic interactions in the cluster. The experimental maximum magnetic entropy change (−ΔS_m) is calculated to be 44.9 J kg⁻¹ K⁻¹ at 2 K for ΔH = 7 T using the Maxwell equation, (Fig. 4b). This experimental value is smaller than the theoretical value of 60.0 J kg⁻¹ K⁻¹ (based on the equation S_m = R ln(2S + 1) for 44 uncorrelated Gd³⁺ and 22 uncorrelated Ni²⁺ ions). The smaller experimental value might also be attributed to the presence of weak antiferromagnetic interactions.

Fig. 4 (a) Field dependence of isothermal normalized magnetizations at 2–10 K; (b) plots of experimental magnetic entropy change (−ΔS_m) vs. temperature (T) of the wheel-like {Gd₄₄Ni₂₂} cluster.

It is worth noting that the {Gd₄₄Ni₂₂} cluster demonstrates a large MCE, comparable to that of the recently reported high-nucleation cluster {Gd₁₅₈Co₃₈}³⁸ (−ΔS_m = 46.95 J kg⁻¹ K⁻¹ at 2.0 K for ΔH = 7 T). It is also significantly larger than that of other wheel-like 3d-Gd(III) clusters (Table S4†), such as {Gd₂₄Co₁₆}³² (−ΔS_m = 26.0 J kg⁻¹ K⁻¹ at 3.8 K for ΔH = 7 T) and {Gd₂₄Cu₃₆}³¹ (−ΔS_m = 21.0 J kg⁻¹ K⁻¹). Meanwhile, the MCE of 1 is also among the largest when compared with the reported homometallic Gd-clusters (Table S4†), demonstrating its great potential for magnetic cooling.

The large MCE of {Gd₄₄Ni₂₂} may be attributed to the following reasons: first, by using ligands with a large number of coordination sites and minor steric hindrances, such as IDA and H₃dmpa, we are able to bond and stabilize a large number of metal ions in a relatively compact fashion. This results in a large metal/ligand ratio to ensure a high magnetic density for the large MCE. Second, Gd³⁺ effectively increases the distance between Ni²⁺ ions (i.e., to 5.195–5.272 Å), and hence reduces the magnetic coupling between adjacent Ni²⁺ ions. Still, we notice weak antiferromagnetic couplings in 1 (θ = −5.3 K), indicating that further structural tuning might help to avoid the magnetic interaction and further enhance the MCE of 1.

Conclusion

In summary, a novel wheel-like 3d-Gd cluster, {Gd₄₄Ni₂₂}, is synthesized by adopting the “mixed-ligand” strategy. As a promising magnetic cooling material, {Gd₄₄Ni₂₂} demonstrates a large MCE, with −ΔS_m of 44.9 J kg⁻¹ K⁻¹ at 2 K under 7 T. This value is one of the highest among all known high-nuclearity 3d–4f clusters. The large MCE is caused by the high metal/ligand ratio, which leads to high magnetic density. Further studies on tuning the cluster structure to reduce antiferromagnetic interactions and enhance the MCE of 1 are underway and will be reported in our forthcoming contribution.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the NSF of China (21871262 and 21901242), the NSF of Fujian Province (2020J05080), the NSF of Xiamen (3502Z20206080), the Key Research Program of the Chinese Academy of Sciences (ZDRW-CN-2021-3-3), the Youth Innovation Promotion Association CAS (2021302), the Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China (2021ZR110), and the Recruitment Program of Global Youth Experts.

References

1. T. Liu, E. Diemann, H. Li, A. W. M. Dress and A. Müller, Self-assembly in aqueous solution of wheel-shaped Mo154 oxide clusters into vesicles, Nature, 2003, 426, 59–62.
2. I. Colliard, J. C. Brown, D. B. Fast, A. K. Sockwell, A. E. Hixon and M. Nyman, Snapshots of Ce70 toroid assembly from solids and solution, J. Am. Chem. Soc., 2021, 143, 9612–9621.
3. B. Russell-Webster, J. Lopez-Nieto, K. A. Abboud and G. Christou, Truly monodisperse molecular nanoparticles of cerium dioxide of 2.4 nm dimensions: A {Ce100O167} cluster, Angew. Chem., Int. Ed., 2021, 60, 12591–12596.
4. X. X. Hang, B. Liu, X. F. Zhu, S. T. Wang, H. T. Han, W. P. Liao, Y. L. Liu and C. H. Hu, Discrete {Ni40} coordination cage: A calixarene-based Johnson-Type (J17) hexadecahedron, J. Am. Chem. Soc., 2016, 138, 2969–2972.
5. C. D. Wu, C. Z. Lu, H. H. Zhuang and J. S. Huang, Hydrothermal assembly of a novel three-dimensional framework formed by [GdMo₁₂O₄₂]₉⁻ anions and nine coordinated GdIII cations, J. Am. Chem. Soc., 2002, 124, 3836–3837.
6. X. M. Luo, S. Huang, P. Luo, K. Ma, Z. Y. Wang, X. Y. Dong and S. Q. Zang, Snapshots of key intermediates unveiling the growth from silver ions to Ag70 nanoclusters, Chem. Sci., 2022, 13, 11110–11118.
7. Y. F. Bi, X. T. Wang, W. P. Liao, X. F. Wang, X. W. Wang and H. J. Zhang, A {Co32} nanosphere supported by p-tert-butylthiacalix[4]arene, J. Am. Chem. Soc., 2009, 131, 11650–11651.
8. E. G. Ribó, N. L. Bell, W. M. Xuan, J. C. Luo, D. L. Long, T. B. Liu and L. Cronin, Synthesis, assembly, and sizing of neutral, lanthanide substituted molybdenum blue wheels {Mo90Ln10}, J. Am. Chem. Soc., 2020, 142, 17508–17514.
9. S. Kenzler and A. Schnepf, Metalloid gold clusters – Past, current and future aspects, Chem. Sci., 2021, 12, 3116–3129.
10. Z. G. Jiang, W. H. Wu, B. X. Jin, H. M. Zeng, Z. G. Jin and C. H. Zhan, A chloride-doped silver-sulfide cluster [Ag₁₄₈S₂₆Cl₃₀ (C=CBut)60]⁶⁺: Hierarchical assembly, enhanced luminescence and cytotoxicity to cancer cells, Nanoscale, 2022, 14, 1971–1977.
11. L. Qin, Y. Z. Yu, P. Q. Liao, W. Xue, Z. P. Zheng, X. M. Chen and Y. Z. Zheng, A “molecular water pipe”: A giant tubular cluster {Dy72} exhibits fast proton transport and slow magnetic relaxation, Adv. Mater., 2016, 28, 10772–10779.
12. X. M. Luo, Z. B. Hu, Q. F. Lin, W. W. Cheng, J. P. Cao, C. H. Cui, H. Mei, Y. Song and Y. Xu, Exploring the performance improvement of magnetocaloric effect based Gd-exclusive cluster Gd60, J. Am. Chem. Soc., 2018, 140, 11219–11222.
13. H. J. Lun, L. Xu, X. J. Kong, L. S. Long and L. S. Zheng, A high-symmetry double-shell Gd₃₀Co₁₂ cluster exhibiting a large magnetocaloric effect, Inorg. Chem., 2021, 60, 10079–10083.
14. V. Corradini, A. Ghirri, A. Candini, R. Biagi, U. D. Pennino, G. Dotti, E. Otero, F. Choueikani, R. J. Blagg, E. J. L. McInnes and M. Affronte, Magnetic cooling at a single molecule level: a spectroscopic investigation of isolated molecules on a surface, Adv. Mater., 2013, 25, 2816–2820.
15. J. B. Peng, Q. C. Zhang, X. J. Kong, Y. Z. Zheng, Y. P. Ren, L. S. Long, R. B. Huang, L. S. Zheng and Z. P. Zheng, High-nuclearity 3d–4f clusters as enhanced magnetic coolers and molecular magnets, J. Am. Chem. Soc., 2012, 134, 3314–3317.
16. P. Konieczny, W. Sas, D. Czernia, A. Pacanowska, M. Fitta and R. Pełka, Magnetic cooling: A molecular perspective, Dalton Trans., 2022, 51, 12762–12780.
17. X. Y. Zheng, X. J. Kong, Z. P. Zheng, L. S. Long and L. S. Zheng, High-nuclearity lanthanide-containing clusters as potential molecular magnetic coolers, Acc. Chem. Res., 2018, 51, 517–525.
18. E. Warburg, Magnetische untersuchungen, Ann. Phys., 1881, 249, 141–164.
19. P. Debye, Einige Bemerkungen zur Magnetisierung bei tiefer Temperatur, Ann. Phys., 1926, 386, 1154–1160.
20. W. F. Giauque, A thermodynamic treatment of certain magnetic effects. A proposed method of producing temperatures considerably below 1 absolute, J. Am. Chem. Soc., 1927, 49, 1864–1870.
21. O. Tegus, E. Bruck, K. H. J. Buschow and F. R. de Boer, Transition-metal-based magnetic refrigerants for room-temperature applications, Nature, 2002, 415, 150–152.
22. F. Torres, J. M. Hernández, X. Bohigas and J. Tejada, Giant and time-dependent magnetocaloric effect in high-spin molecularmagnets, Appl. Phys. Lett., 2000, 77, 3248–3250.
23. T. Lis, Preparation, structure, and magnetic properties of a dodecanuclear mixed-valence manganese carboxylate, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1980, 36, 2042.
24. D. Gatteschi, A. Caneschi, L. Pardi and R. Sessoli, Large clusters of metal ions: The transition from molecular to bulk magnets, Science, 1994, 265, 1054.
25. J. W. Sharples, Y. Z. Zheng, F. Tuna, E. J. McInnes and D. Collison, Lanthanide discs chill well and relax slowly, Chem. Commun., 2011, 47, 7650–7652.
26. J. B. Peng, X. J. Kong, Q. C. Zhang, M. Orendac, J. Prokleska, Y. P. Ren, L. S. Long, Z. Zheng and L. S. Zheng, Beauty, symmetry, and magnetocaloric effect four-shell keplerates with 104 lanthanide atoms, J. Am. Chem. Soc., 2014, 136, 17938–17941.
27. F. S. Guo, Y. C. Chen, L. L. Mao, W. Q. Lin, J. D. Leng, R. Tarasenko, M. Orendáč, J. Prokleška, V. Sechovsky and M. L. Tong, Anion-templated assembly and magnetocaloric properties of a nanoscale {Gd38} cage versus a {Gd48} barrel, Chem. – Eur. J., 2013, 19, 14876–14885.
28. W. P. Chen, P. Q. Liao, P. B. Jin, L. Zhang, B. K. Ling, S. C. Wang, Y. T. Chan, X. M. Chen and Y. Z. Zheng, The gigantic {Ni₃₆Gd₁₀₂} hexagon: A sulfate-templated “star-of-David” for photocatalytic CO₂ reduction and magnetic cooling, J. Am. Chem. Soc., 2020, 142, 4663–4670.
29. W. P. Chen, P. Q. Liao, Y. Yu, Z. Zheng, X. M. Chen and Y. Z. Zheng, A mixed–ligand approach for a gigantic and hollow heterometallic cage {Ni₆₄RE₉₆} for gas separation and magnetic cooling applications, Angew. Chem., Int. Ed., 2016, 55, 9375–9379.
30. Q. F. Lin, J. Li, X. M. Luo, C. H. Cui, Y. Song and Y. Xu, Incorporation of silicon–oxygen tetrahedron into novel high-nuclearity nanosized 3d–4f heterometallic clusters, Inorg. Chem., 2018, 57, 4799–4802.
31. J. D. Leng, J. L. Liu and M. L. Tong, Unique nanoscale {CuII 36 LnIII 24}(Ln = Dy and Gd) metallo-rings, Chem. Commun., 2012, 48, 5286–5288.
32. Z. M. Zhang, L. Y. Pan, W. Q. Lin, J. D. Leng, F. S. Guo, Y. C. Chen, J. L. Liu and M. L. Tong, Wheel-shaped nanoscale 3d–4f {Co II 16 Ln III 24} clusters (Ln = Dy and Gd), Chem. Commun., 2013, 49, 8081–8083.
33. X. Y. Zheng, Y. H. Jiang, G. L. Zhuang, D. P. Liu, H. G. Liao, X. J. Kong, L. S. Long and L. S. Zheng, A gigantic molecular wheel of {Gd140}: A new member of the molecular Wheel Family, J. Am. Chem. Soc., 2017, 139, 18178–18181.
34. C. Benelli and D. Gatteschi, Magnetism of lanthanides in molecular materials with transition-metal ions and organic radicals, Chem. Rev., 2002, 102, 2369.
35. O. Kahn, Molecular Magnetism, VCH, New York, 1993.
36. Y. Z. Zheng, G. J. Zhou, Z. Zheng and R. E. P. Winpenny, Molecule-based magnetic coolers, Chem. Soc. Rev., 2014, 43, 1462–1475.
37. J. L. Liu, Y. C. Chen, F. S. Guo and M. L. Tong, Recent advances in the design of magnetic molecules for use as cryogenic magnetic coolants, Coord. Chem. Rev., 2014, 281, 26–49.
38. N. F. Li, X. M. Min, J. Wang, J. L. Wang, Y. Song, H. Mei and Y. Xu, Largest 3d–4f 196-nuclear Gd₁₅₈Co₃₈ clusters with excellent magnetic cooling, Sci. China: Chem., 2022, 65, 1577–1583.

---

Footnote

† Electronic supplementary information (ESI) available: The synthesis; the crystallographic data; the selected bond distance table; the selected bond valence analysis; the decay analysis data; XRD; SEM; IR; TG-DSC. CCDC 2208968 for 1. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d2qi02294j

---