English

• 0.   Introduction

  The design and construction of novel and interesting high‐nuclear lanthanide clusters with multifunctional properties have always received great attention from coordination chemists and materials scientists^[1-2]. Up to now, lots of high‐nuclear Ln (Ⅲ)‐based clusters with different topological structures such as cage shape, spherical, wheel, and hamburger have been constructed^[3-5]. Although a good deal of high‐nuclear Ln(Ⅲ)‐based clusters with different functions have been constructed^[6], the effective approach for designing and constructing these clusters with specific shapes and excellent function are still lacking^[7]. With the development of crystallography and the expansion of properties of Ln (Ⅲ)‐based clusters, progress has been made in the structural design and functional study of high‐nucleation Ln (Ⅲ)‐based clusters^[8]. These high‐nuclear Ln (Ⅲ)‐based clusters have been widely studied in the fields of magnetocaloric effect^[9], catalysis^[10], near‐infrared (NIR) luminescence^[11], and biology^[12]. For the NIR luminescence, Ln (Ⅲ)‐based clusters may exhibit interesting properties, for example, long lifetimes, sharp emission spectra, and large Stokes shifts. The group of Yang did lots of good work in the design of NIR luminescent high‐nuclearity Ln (Ⅲ)‐based clusters^[13-15]. In 2019, Yang and co‐workers reported an Nd₉ nanocluster that can display NIR luminescence of Nd³⁺ ions and exhibit luminescence response to both metal ions and nitro explosives^[16]. Whereafter, a high‐nuclearity elliptical Yb (Ⅲ) nanoring showing NIR luminescent response to metal ions and nitro explosives has been reported by Yang′s group in 2020^[17]. In 2021, Yang′s group reported an Nd₁₄ cluster that displays NIR luminescence sensing properties towards metal cations and anions^[18]. These studies indicate that high‐nuclear Ln(Ⅲ)‐based clusters have wide and considerable applications in NIR luminescent.

  On the other hand, in the catalysis area, Ln (Ⅲ)‐based compounds as catalysts for the conversion of CO₂ into high‐value‐added chemicals more and more become a research hotspot in recent years^[19]. Among these catalytic reactions, the most interesting and attractive one is the reaction between epoxides and CO₂ to obtain cycle carbonates^[20]. As a catalyst, the Ln(Ⅲ)‐based compound has natural advantages: (1) the central Ln³⁺ ions can act as possible Lewis acidic sites and enhance catalytic activity; (2) it can show some intrinsic characteristics and rich coordination patterns; (3) the porous Ln (Ⅲ)‐based compound can effectively adsorb CO₂^[21]. In this regard, it is especially important to design and synthesize Ln(Ⅲ)‐based clusters as heterogeneous catalysts for coupling CO₂ and epoxides to obtain cyclic carbonates. Until now, some Ln(Ⅲ)‐based MOFs or compounds catalysts have been reported for such types of catalytic reaction^[22-23], and a few of them show high efficiency in CO₂ conversion^[24-25]. Hence, the Ln (Ⅲ)‐based compounds as catalysts have excellent prospects for CO₂ fixation reactions.

  Herein, by using a polydentate‐chelating ligand (H₂L) to react with Yb(acac)₃·2H₂O, a novel Yb₈ cluster, formulated as [Yb₈(acac)₄(HL)₄(L)₂(μ₃‐O)₄(C₂H₅O)₄]· 2C₂H₅OH·2CH₂Cl₂ (1), has been designed and synthesized under solvothermal conditions (Scheme 1). The X‐ray diffraction analysis reveals that cluster 1 shows an octanuclear structure and the four asymmetrically centered Yb(Ⅲ) ions possesses different geometrical configuration. A notable detail is that cluster 1 displayed excellent solvent stability after soaking in various organic solvents for 12 h. Furthermore, the photoluminescence property study reveals that 1 showed typical NIR luminescence of Yb (Ⅲ) at room temperature. What′s more, cluster 1 acted as a catalyst and showed high catalytic activity for the cycloaddition reaction of CO₂ and epoxides.

  Scheme 1

  

  Scheme 1.  Synthetic schematic of organic ligand H₂L (a) and cluster 1 (b)

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  1.   Experimental

  1.1   Material and measurement

  5‐Hydroxymethylfurfural, 2‐salicylhydrazide, and dysprosium nitrate hexahydrate (Yb(NO₃)₃·6H₂O) were bought at Energy Chemical Co., Ltd. The common solvents (ethanol, acetonitrile, and dichloromethane) were purchased from Komeo Reagent Co., Ltd. According to the previously reported method^[26], the multidentate Schiff base ligand (H₂L) has been synthesized. Yb(acac)₃·2H₂O was prepared according to the method reported in the literature^[27].

  Elemental analysis for compound 1 was performed on a Perkin‐Elmer 2400 analyzer. Infrared spectra data were gained with a Bruker TENOR 27 spectrophotometer. Powder X‐ray diffraction (PXRD) data were collected using a Rigaku Ultima Ⅳ instrument with Cu Kα radiation (λ=0.154 056 nm) in a 2θ range of 5°‐50°; the operating voltage and current were 40 kV and 25 mA, respectively. Thermogravimetric (TG) analysis data were recorded using a NETZSCHTG 409 PC thermal analyzer.

  1.2   Synthesis of Schiff base ligand (H₂L) and cluster 1

  5‐hydroxymethylfurfural (1.89 g, 15 mmol) was dissolved in 50 mL of absolute methanol, then, 2‐salicyl hydrazide (2.28 g, 15 mmol) was added and refluxed at 80 ℃ for about 12 h. The resulting yellow solid was filtered under a vacuum, washed with methanol, and dried under a vacuum at 70 ℃ for about 72 h to give H₂L. Yield: 2.83 g (76%). Anal. Calcd. for C₁₂H₁₂N₂O₄ (%): C, 58.06; H, 4.84; N, 11.29. Found(%): C, 58.09; H, 4.86; N, 11.26. Selected IR (KBr, cm^-1): 3 416 (w), 3 245 (s), 2 938 (w), 2 730 (w), 1 598 (s), 1 605 (w), 1 551 (s), 1 492 (m), 1 456 (s), 1 375 (m), 1 348 (w), 1 310 (m), 1 240 (s), 1 145 (m), 1 099 (w), 1 013 (m), 965 (w), 908 (m), 785 (m), 751 (s), 665 (m), 635 (m), 562 (w), 448 (w) (Fig.S1, Supporting information).

  H₂L (0.04 mmol) and Yb(acac)₃·2H₂O (0.04 mmol) were mixed in the C₂H₅OH (9.0 mL) and CH₂Cl₂ (4.0 mL) solution. The above mixture was sealed in a 20 mL glass vial and heated at 70 ℃ for 2 d. After the reaction temperature was slowly decreased to room temperature, yellow block‐shaped crystals were obtained. Yield: 37% (Based on Yb(acac)₃·2H₂O). Elemental analysis Calcd. for C₁₁₂H₁₂₂C_l4N₁₂O₄2Yb₈(%): C: 35.53; H: 3.20; N: 4.48; Found(%): C: 35.49; H: 3.23; N: 4.50. IR(KBr, cm^-1, Fig.S1): 3 623 (w), 3 407 (m), 3 018 (w), 2 877 (m), 1 598 (s), 1 559 (w), 1 510 (s), 1 447 (s), 1 360 (s), 1 305 (w), 1 266 (m), 1 204 (m), 1 188 (w), 1 135 (s), 1 013 (s), 935 (m), 920 (m), 847 (w), 808 (m), 760 (s), 701 (m), 667 (m), 618 (w), 515 (s), 467 (w).

  1.3   Catalytic reaction of CO₂ and epoxides

  Firstly, cluster 1 (x=0.5%), TBAB (x=3%), substrate (2 mmol), and abundant CO₂ were sealed in a 20 mL Schlenk tube, then the mixture was stirred for 12 h at different temperatures (T=30‐90 ℃). After reacting completely, the obtained mixture was dissolved in CH₂Cl₂ (2 mL) and the products were purified by column chromatography. The yield of the corresponding product was characterized by ¹H NMR spectroscopy with 1, 3, 5‐trimethoxybenzene (TMS) as the internal standard.

  1.4   X-ray crystallography

  A suitable single crystal of cluster 1 was selected for the X‐ray diffraction analysis. The data were collected through a Bruker Apex Ⅱ CCD diffractometer with graphite‐monochromated Mo Kα radiation (λ= 0.071 073 nm) at 150 K by using the φ‐ω scan technique. The structure for 1 was directly solved using SHELXL and Olex2 programs^[28]. All non‐hydrogen atoms were refined by full‐matrix least‐squares methods on F². Due to the disorder of free molecules, the SQUEEZE procedure in the PLATON software was used for 1. Crystallographic parameters of cluster 1 are given in Table 1. The selected bond lengths and bond angles of cluster 1 are listed in Table S1.

  Table 1

  

  Table 1.  Crystallographic data and structure refinements for cluster 1

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  Parameter	1		Parameter	1
  Formula	C112H122Cl4N12O42Yb8		Z	1
  Formula weight	3 834.33		Crystal size/mm	0.28×0.21×0.14
  T/K	149.99		Dc/(g·cm-3)	1.883
  Cryst system	Triclinic		μ/mm-1	5.634
  Space group	P1		Limiting indices	-19 ≤ h ≤19, -19 ≤ k ≤ 19, -20 ≤ l ≤ 20
  a/nm	1.545 01(9)		Reflection collected	57 976
  b/nm	1.572 63(10)		Unique	13 182
  c/nm	1.677 62(11)		Number of parameters	786
  α/(°)	68.403(3)		Rint	0.114 9
  β/(°)	63.289(3)		GOF on F2	1.028
  γ/(°)	82.975(3)		R1, wR2 [I > 2σ(I)]	0.057 7, 0.132 2
  V/nm3	3.381 0(4)		R1, wR2 (all data)	0.098 5, 0.149 8

  2.   Results and discussion

  2.1   Crystal structure of cluster 1

  Single‐crystal X‐ray diffraction results revealed that cluster 1 crystallizes in the P1 space group of the triclinic system. As shown in Fig. 1, cluster 1 mainly consists of eight Yb(Ⅲ) ions, four HL^- ions, two L^2- ions, four μ₃‐O atoms, four acac^- ions, and four C₂H₅O^- ions. As depicted in Fig. S2, the central Yb1 (Ⅲ) is eight‐coordinated and surrounded by seven oxygen atoms (O4, O6, O13, O14, O17, O18, and O20) and one nitrogen atom (N4); while the Yb2(Ⅲ), Yb3(Ⅲ) and Yb4(Ⅲ) are seven‐coordinated with different coordination environments. The coordination polyhedrons of the four central Yb1, Yb2, Yb3, and Yb4 atoms can be described as a distorted bi‐augmented trigonal prism, capped trigonal prism, pentagonal bipyramid, and capped octahedron geometrical configuration (Fig. 2), respectively; which could be confirmed by using the SHAPES 2.0 software (Table S2). As shown in Fig. 3, H₂L adopts two different coordination modes connected to the central Yb (Ⅲ) ions. In the asymmetric Yb₄ core, the four Yb (Ⅲ) ions are connected by two μ₃‐O atoms and four μ₂‐O atoms forming two defective cubanes (Fig. S3). The eight Yb(Ⅲ) ions are bridged by eight μ₂‐O atoms, two μ₃‐O atoms, and two μ₄‐O atoms forming a Yb₈ core (Fig.S4). In the Yb₄ core, the distances of two Yb(Ⅲ) ions are in a range of 0.352 26(8)‐0.642 90(8) nm, the bone angles for Yb—Yb—Yb are in a range of 55.809(2)°‐123.345(2)°. In addition, the bond lengths of Yb—O/N are in a range of 0.217 2(7)‐0.246 8(10) nm; and the O—Yb—O bond angles are in a range of 64.6(2)°‐165.5(3)°. These bond lengths and angles in cluster 1 are comparable to those of the recently reported polynuclear or high‐nuclear Ln (Ⅲ)‐based clusters in the literature^[29-32].

  Figure 1

  

  Figure 1.  Molecular structure of cluster 1

  Hydrogen atoms have been omitted; Symmetry code: a: -x+1, -y, -z+1

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  Figure 2

  

  Figure 2.  Coordination polyhedrons for Yb1(Ⅲ), Yb2(Ⅲ), Yb3(Ⅲ), and Yb4(Ⅲ) ions in 1

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  Figure 3

  

  Figure 3.  Two coordination modes of H₂L in cluster 1

  Hydrogen atoms have been omitted, Symmetry code: a: -x+1, -y, -z+1

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  2.2   PXRD and TG analyses

  PXRD for cluster 1 was carried out at room temperature. As shown in Fig. S5, the experimental data were good agree with the theoretical values calculated by single crystal structure simulation, indicating the high phase purity. In order to explore and study the solvent stability of cluster 1, as‐synthesized samples were immersed in nine common solvents, namely H₂O, methanol (MeOH), ethanol (EtOH), n‐propanol (n‐PrOH), dichloromethane (CH₂Cl₂), acetonitrile (MeCN), n‐hexane, N, N‐dimethylformamide (DMF), and N, N‐dimethylacetamide (DMA) for about 12 h. As shown in Fig. 4, the PXRD analyses reveal that these samples for 1 had excellent solvent stability. The thermal stability of cluster 1 was studied by TG analysis under an N₂ atmosphere, and the TG and differential thermogravimetric (DTG) curves are shown in Fig. S6. The weight loss of 4.61% between 30 and 250 ℃ can be attributed to the loss of two free C₂H₅OH molecules and a free CH₂Cl₂ molecule (Calcd. 4.72%), after which cluster 1 slowly decomposed. From the above thermogravimetric analysis, cluster 1 can maintain structural stability before 250 ℃ at least, and it possesses better thermal stability.

  Figure 4

  

  Figure 4.  PXRD patterns of cluster 1 after being immersed in different solvents for 12 h

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  2.3   UV-Vis spectra

  The UV‐Vis spectra for Yb(acac)₃·2H₂O, H₂L, and cluster 1 have been performed at room temperature (Fig.S7). For Yb(acac)₃·2H₂O, two absorption peaks at 202 and 291 nm were observed. For H₂L and cluster 1, the UV‐Vis absorption spectra showed that absorption bands of the free ligand H₂L (201, 226, and 328 nm) were red‐shifted in 1 (203, 256, and 359 nm). The absorption peak at 307 nm in 1 resulted from the peak (291 nm) of Yb(acac)₃·2H₂O, which was slightly red‐shifted. Compared with H₂L, the peak at 256 nm gradually disappeared, which may result from the coordination effects among H₂L and Yb(Ⅲ) ions in 1.

  2.4   NIR luminescence property

  The NIR emission spectra of cluster 1 were investigated in CH₃OH (Fig. 5a). Upon excitation of 359 nm, cluster 1 showed the typical NIR luminescence of Yb (Ⅲ) at 976, 1 008, and 1 038 nm (²F_5/2 → ²F_7/2), which suggests the energy transfer from the organic ligands to the Yb(Ⅲ) ions in cluster 1. The NIR luminescence lifetime (τ) and quantum yield (Φ_em) of cluster 1 are 8.91 μs and 0.21%, respectively (Fig. 5b). Hence, the intrinsic quantum yield (Φ_Ln) of Yb (Ⅲ) ions and ligand‐to‐metal energy transfer (LMET) efficiency (η_sens) in cluster 1 were estimated to be 0.45% and 46.7%, respectively (Φ_Ln=τ/τ₀, the natural lifetime (τ₀) of Yb(Ⅲ) was 2 000 μs; and η_sens=Φ_em/Φ_Ln).

  Figure 5

  

  Figure 5.  (a) NIR luminescence for cluster 1 in CH₃OH at room temperature (λ_ex=392 nm); (b) NIR emission lifetime of 1 in CH₃OH

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  2.5   Catalytic studies

  Considering the abundant Lewis acid active sites of Yb (Ⅲ) ions in cluster 1^[33], herein, we explored and studied the reactions of CO₂ with epoxides. Epichlorohydrin was selected as a model substrate to investigate optimized reaction conditions, which is listed in Table 2. Generally speaking, the temperature is an important factor for catalyst reactions. Therefore, the influence of the temperature on the reaction was investigated (Table 2, Entry 1‐8). The yield increased with the rise in temperature, and a high yield (97%) of 4‐(chloromethyl)‐1, 3‐dioxolan‐2‐one was achieved at 70 ℃. Nevertheless, the yield at 80 and 90 ℃ decreased to some extent, which might be ascribed to the partial decomposition of TBAB (tetrabutylammonium bromide) at a high temperature. As a result, the optimal reaction conditions were x=2.5% for cluster 1 (based on Yb), x=3.0% for co‐catalyst TBAB under solvent‐free conditions, and a CO₂ pressure of 101.325 kPa at 70 ℃ for 12 h (Table 2, Entry 6). Furthermore, under the optimized reaction conditions, the yield was only 37% when cluster 1 was absent (Table 2, Entry 9), and the yields were much lower when we used various Yb(Ⅲ)‐based salts instead of catalyst 1 (Table 2, Entry 11‐14). It indicates that salt cannot effectively catalyze the reaction and cluster 1 can largely improve the yield of cycloaddition reactions and is an effective catalyst. Moreover, when only catalyst 1 in the absence of TBAB was used for the cycloaddition of CO₂ with epichlorohydrin, the yield was negligible (Table 2, Entry 10), suggesting that TBAB also plays an important role in the system.

  Table 2

  

  Table 2.  CO₂ reacting with epichlorohydrin under different conditions^a

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  Entry	Catalyst	xTBAB/%	T/℃	Yieldb/%
  1	Cluster 1	3	20	43
  2	Cluster 1	3	30	52
  3	Cluster 1	3	40	65
  4	Cluster 1	3	50	79
  5	Cluster 1	3	60	93
  6	Cluster 1	3	70	97
  7	Cluster 1	3	80	95
  8	Cluster 1	3	90	94
  9	—	3	70	37
  10	Cluster 1	—	70	< 1
  11	Yb(NO3)3·6H2O	3	70	21
  12	YbCl3·6H2O	3	70	19
  13	Yb(Ac)3·6H2O	3	70	23
  14	Yb(acac)3·2H2O	3	70	28
  a Reaction conditions: nepichlorohydrin=2.0 mmol, xcatalyst=2.5%, pCO2=101.325 kPa, 12 h, solvent‐free; b Determined by 1H NMR spectroscopy with 1, 3, 5‐trimethoxybenzene as an internal standard.

  To further explore and study the catalytic generality of cluster 1, as shown in Table 3, a series of typical epoxides were examined for the cycloaddition reaction under optimized reaction conditions. All the epoxides can be converted to the corresponding cyclic carbonates in excellent yields (79%‐96%, Table 3) under mild temperature (70 ℃) and pressure (101.325 kPa) after 12 h. In comparison, the cycloaddition of CO₂ to isobutylene oxide or tert‐butyl glycidyl ether (Table 3, Entry 3 and 8) had a slightly lower yield owing to the presence of steric hindrance^[34]. These results clearly show that cluster 1 can catalyze the cycloaddition reaction with relatively extensive epoxides.

  Table 3

  

  Table 3.  Various carbonates from CO₂ reacted with different epoxides catalyzed by cluster 1 under optimized conditions^a

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  Entry	Substrate	Product	Yieldb/%
  1			93
  2			91
  3			79
  4			89
  5			96
  6			94
  7			91
  8			86
  a Reaction conditions: nepoxides=2.0 mmol, x1=2.5%, xTBAB=3%, pCO2=101.325 kPa, 70 ℃, 12 h, solvent ‐ free; b Determined by 1H NMR spectroscopy with 1, 3, 5 ‐ trimethoxybenzene as an internal standard.

  Commonly, cyclicity is an essential feature of any catalyst considered for heterogeneous catalysis in industrial applications. Here, we evaluated the recyclability of cluster 1, as shown in Fig. 6, cluster 1 could be reused at least three times almost without any obvious loss in catalytic activity for the cycloaddition of CO₂ with epichlorohydrin. Moreover, the IR and PXRD analyses of the reused catalyst 1 were carried out, which matched well with the fresh one or simulated one from 1 (Fig. 7 and 8), revealing that the framework of catalyst 1 still remains intact after the catalytic reaction. The filtrate of the last recycling cycle has been measured by inductively coupled plasma (ICP), and only 0.44 mg·L^-1 Yb(Ⅲ) ion of leakage from the framework of catalyst 1 was detected (Table S3), which also confirms the heterogeneous nature of the reaction. Compared with some Ln (Ⅲ)‐based MOFs or compounds as heterogeneous catalysts in recent literature^[35-36], cluster 1 displayed well catalytic activity under mild conditions.

  Figure 6

  

  Figure 6.  Recycle tests of 1 for the transformation reaction of CO₂ with epichlorohydrin

  Reaction conditions: n_{epichlorohydrin}=2.0 mmol, x₁=2.5%, x_TBAB=3%, p_CO2=101.325 kPa, 12 h, solvent‐free

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  Figure 7

  

  Figure 7.  IR spectra of cluster 1 and the recycled catalyst after reactions

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  Figure 8

  

  Figure 8.  PXRD patterns of cluster 1 and the recycled catalyst after reactions

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  Based on the previously reported mechanism of the cycloaddition of CO₂ and epoxides^[37-39], we propose a possible reaction mechanism (Fig. 9). First, epoxides are activated by the strong Lewis acidic Yb (Ⅲ) sites in catalyst 1. Then the Br^- acting as the nucleophile attacks the C atom of methylene on the less sterically hindered side of the epoxides, which promotes the ringopening of the epoxides effectively. Meanwhile, CO₂ is simultaneously inserted in the opened epoxides forming alkyl carbonate salts. Finally, the corresponding products have been obtained through ring closure along with the regeneration of catalyst 1. In the catalytic reaction, cluster 1 displays significant catalytic activity which is mainly due to the high density of Lewis acidic Yb(Ⅲ) ions and the vacant coordination sites (seven‐or eight‐coordinated) of Yb(Ⅲ) ions in 1.

  Figure 9

  

  Figure 9.  A tentative mechanism for the cycloaddition reaction

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  3.   Conclusions

  In summary, a novel Yb₈ cluster (1) based on a polydentate Schiff base ligand (H₂L) has been successfully designed and constructed under solvothermal conditions. Cluster 1 exhibits excellent chemical stability under various common solvents. Furthermore, the photoluminescence study shows that 1 displays typical NIR luminescence of Yb (Ⅲ) at room temperature. What′s more, cluster 1 exhibits excellent catalytic activity for the conversion of CO₂ with epoxides, and catalyst 1 can be reused at least three times without obvious loss. Our work provides a new way for designing and constructing of polynuclear lanthanide clusters with multifunctional properties.

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

  
  
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  Scheme 1  Synthetic schematic of organic ligand H₂L (a) and cluster 1 (b)

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  Figure 1  Molecular structure of cluster 1

  Hydrogen atoms have been omitted; Symmetry code: a: -x+1, -y, -z+1

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  Figure 2  Coordination polyhedrons for Yb1(Ⅲ), Yb2(Ⅲ), Yb3(Ⅲ), and Yb4(Ⅲ) ions in 1

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  Figure 3  Two coordination modes of H₂L in cluster 1

  Hydrogen atoms have been omitted, Symmetry code: a: -x+1, -y, -z+1

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  Figure 4  PXRD patterns of cluster 1 after being immersed in different solvents for 12 h

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  Figure 5  (a) NIR luminescence for cluster 1 in CH₃OH at room temperature (λ_ex=392 nm); (b) NIR emission lifetime of 1 in CH₃OH

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  Figure 6  Recycle tests of 1 for the transformation reaction of CO₂ with epichlorohydrin

  Reaction conditions: n_{epichlorohydrin}=2.0 mmol, x₁=2.5%, x_TBAB=3%, p_CO2=101.325 kPa, 12 h, solvent‐free

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  Figure 7  IR spectra of cluster 1 and the recycled catalyst after reactions

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  Figure 8  PXRD patterns of cluster 1 and the recycled catalyst after reactions

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  Figure 9  A tentative mechanism for the cycloaddition reaction

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  Table 1.  Crystallographic data and structure refinements for cluster 1

  Parameter	1		Parameter	1
  Formula	C112H122Cl4N12O42Yb8		Z	1
  Formula weight	3 834.33		Crystal size/mm	0.28×0.21×0.14
  T/K	149.99		Dc/(g·cm-3)	1.883
  Cryst system	Triclinic		μ/mm-1	5.634
  Space group	P1		Limiting indices	-19 ≤ h ≤19, -19 ≤ k ≤ 19, -20 ≤ l ≤ 20
  a/nm	1.545 01(9)		Reflection collected	57 976
  b/nm	1.572 63(10)		Unique	13 182
  c/nm	1.677 62(11)		Number of parameters	786
  α/(°)	68.403(3)		Rint	0.114 9
  β/(°)	63.289(3)		GOF on F2	1.028
  γ/(°)	82.975(3)		R1, wR2 [I > 2σ(I)]	0.057 7, 0.132 2
  V/nm3	3.381 0(4)		R1, wR2 (all data)	0.098 5, 0.149 8

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  Table 2.  CO₂ reacting with epichlorohydrin under different conditions^a

  Entry	Catalyst	xTBAB/%	T/℃	Yieldb/%
  1	Cluster 1	3	20	43
  2	Cluster 1	3	30	52
  3	Cluster 1	3	40	65
  4	Cluster 1	3	50	79
  5	Cluster 1	3	60	93
  6	Cluster 1	3	70	97
  7	Cluster 1	3	80	95
  8	Cluster 1	3	90	94
  9	—	3	70	37
  10	Cluster 1	—	70	< 1
  11	Yb(NO3)3·6H2O	3	70	21
  12	YbCl3·6H2O	3	70	19
  13	Yb(Ac)3·6H2O	3	70	23
  14	Yb(acac)3·2H2O	3	70	28
  a Reaction conditions: nepichlorohydrin=2.0 mmol, xcatalyst=2.5%, pCO2=101.325 kPa, 12 h, solvent‐free; b Determined by 1H NMR spectroscopy with 1, 3, 5‐trimethoxybenzene as an internal standard.

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  Table 3.  Various carbonates from CO₂ reacted with different epoxides catalyzed by cluster 1 under optimized conditions^a

  Entry	Substrate	Product	Yieldb/%
  1			93
  2			91
  3			79
  4			89
  5			96
  6			94
  7			91
  8			86
  a Reaction conditions: nepoxides=2.0 mmol, x1=2.5%, xTBAB=3%, pCO2=101.325 kPa, 70 ℃, 12 h, solvent ‐ free; b Determined by 1H NMR spectroscopy with 1, 3, 5 ‐ trimethoxybenzene as an internal standard.

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