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Article

TmCN@C82: Monometallic Clusterfullerene Encapsulating a Tm3+ Ion

by
Huichao Zhang
,
Jinpeng Xin
,
Huaimin Jin
,
Wenhao Xiang
,
Muqing Chen
,
Yang-Rong Yao
* and
Shangfeng Yang
*
Key Laboratory of Precision and Intelligent Chemistry, Department of Materials Science and Engineering, Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei 230026, China
*
Authors to whom correspondence should be addressed.
Inorganics 2023, 11(8), 323; https://doi.org/10.3390/inorganics11080323
Submission received: 29 June 2023 / Revised: 21 July 2023 / Accepted: 26 July 2023 / Published: 31 July 2023
(This article belongs to the Special Issue Research on Metallofullerenes)
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Abstract

:
Metal cyanide clusterfullerenes (CYCFs) are formed via the encapsulation of a single metal atom and a cyanide unit inside fullerene cages, endowing them with excellent properties in various applications. In this work, we report the synthesis, isolation, and characterizations of the first cases of thulium (Tm)-based CYCFs with the popular C82 carbon cages. The structural elucidation of the two TmCN@C82 isomers was achieved via diverse analytical techniques, including mass spectrometry, Vis-NIR spectroscopy, single-crystal X-ray crystallography, and cyclic voltammetry. The crystallographic analyses unambiguously confirmed the molecular structures of the two TmCN@C82 isomers as TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82. Both TmCN clusters adopt a well-established triangular configuration, with the Tm ion located on the symmetrical plane of the carbon cages. The electronic structures of both TmCN@C82 isomers adopt a Tm3+(CN)−@(C82)2− configuration, exhibiting characteristic spectral and electrochemical properties reminiscent of divalent endohedral metallofullerenes (EMFs). Intriguingly, unlike the divalent Tm2+ ion observed in the mono-metallofullerenes Tm@C2n, a higher oxidation state of Tm3+ is identified in the monometallic TmCN cluster due to bonding with the cyanide anion. This result provides valuable insight into the essential role of the non-metallic endo-units in governing the oxidation state of the metal ion and the electronic behaviors of EMFs.

Graphical Abstract

1. Introduction

Fullerene is an allotropic carbon with a great number of family members differentiated by the number of carbon atoms and structural isomerism [1]. A pristine fullerene comprises 12 pentagons and several hexagons according to the number of carbon atoms, forming a cage-like structure with a hollow cavity. Based on the unique structures of fullerenes, three strategies, including exohedral [2,3,4], cage skeletal [5,6,7], and endohedral [8,9,10] modifications, have been widely employed for the chemical functionalization of fullerenes. In particular, the hollow cavity can serve as a nanoscale container to encapsulate various metal atoms or metal clusters, resulting in the formation of endohedral metallofullerenes (EMFs), which have attracted significant interest due to their unique structures and excellent physical and chemical properties, which are different from those of empty fullerenes, in versatile research fields [11,12,13].
The exploration of EMFs began with the discovery of La@C60 in 1985 [14], which sparked a surge of enthusiasm among researchers in understanding the structures, properties, and potential applications of EMFs. Over the past three decades, remarkable progress has been made, particularly with the identification of the first clusterfullerene, Sc3N@C80, in 1999, which opened doors to the encapsulation of various cluster species [15]. Subsequently, clusterfullerenes have developed dramatically as the most important branch of EMFs, with various clusters, such as metal nitride [15,16,17], carbide [18,19,20,21], oxide [22,23,24,25], sulfide [26,27,28,29], and cyanide [30,31,32,33,34,35,36,37,38,39]. Among them, metal cyanide clusterfullerenes (CYCFs), which feature a distinctive mono-metallic cluster with flexible configurations, provide ideal models for regulating properties in applications such as single-molecule magnets [30,32].
To date, a wide range of CYCFs have been successfully synthesized and characterized [30,31,32,33,34,35,36,37,38,39], including MCN@C76 (M = Y [30], Tb [30], Lu [35]) and MCN@C82 (M = Y [31,38], Tb [32,37], Dy [33], Lu [35], U [34]), and MCN@C84 (M = Y [36,39], Tb [36], and Dy [36]). Notably, the oxidation state of uranium in the UCN cluster remains ambiguous as it can exhibit U(I) or U(III) due to the significant donation bonding from the fullerene cage and CN− cluster to uranium [34]. In contrast, cyanide clusters based on yttrium (Y), terbium (Tb), dysprosium (Dy), and lutetium (Lu) uniformly adopt a fixed oxidation state of +3. However, little is known about tunable lanthanide metals with variable oxidation states, such as thulium (Tm), which generally exhibit +2 or +3 oxidation states in fullerenes [40,41,42,43,44]. In addition, compared to the extensively studied rare earth metals, there have been limited reports on Tm-based EMFs, despite their promising applications as fluorescent probes. For example, Shinohara and co-workers demonstrated that the divalent Tm2+ in Tm@C88 isomers and trivalent Tm3+ in Tm2C2@C82 isomers exhibit characteristic photoluminescence at 1200 and 1300–2000 nm, respectively, owing to their distinct energy level transitions [45]. Hence, it is highly desirable to explore novel Tm-based EMFs to gain insights into their bonding, structures, and applications based on their variable oxidation states.
Herein, we report the synthesis, isolation, and characterizations of the first Tm-based EMFs, TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, which, to the best of our knowledge, represent the first isolated Tm-based CYCFs. These two compounds were characterized well via mass spectrometry, single-crystal X-ray diffraction, visible-near-infrared (Vis-NIR) spectroscopy, and cyclic voltammetry. The crystallographic analysis revealed a triangular configuration of the TmCN cluster within both fullerene cages. The electronic structures of both TmCN@C82 isomers are proposed to exhibit a Tm3+(CN)−@(C82)2− configuration, displaying characteristic spectral and electrochemical properties reminiscent of divalent EMFs. Notably, a higher oxidation state of Tm3+ in the mono-metallic TmCN cluster, in contrast to the divalent Tm2+ observed in mono-metallofullerenes Tm@C2n, can be attributed to the presence of the encapsulated cyanide anion.

2. Results and Discussion

Soot containing Tm-based cyanide clusterfullerenes was synthesized utilizing a modified Krätschmer–Huffman direct current (DC) arc discharge method [46]. Briefly, graphite rods were densely packed with graphite powder, Tm2O3, and TiO2, which acts as a catalyst to enhance the yields of the Tm-based cyanide clusterfullerenes. The molar ratio of C/Tm/Ti was maintained at 15/1/1, and the arc-discharge synthesis was performed under a low-vacuum atmosphere with 200 mbar He and 10 mbar N2. The two targeted TmCN@C82 isomers were extracted from the carbon soot samples using the Soxhlet extraction method, followed by isolation via multiple-stage high-performance liquid chromatography (HPLC). The high purity of the isolated TmCN@C82 isomers was verified by observing a solitary peak in the HPLC chromatograms via an analytical Buckyprep column, as depicted in Figure 1. The inserted mass spectra of the two TmCN@C82 isomers also exhibited a solitary peak at m/z = 1179, further confirming their high purity. In addition, the experimental isotopic distributions of the two TmCN@C82 isomers show good agreement with the theoretical predictions.
The molecular structures of the TmCN@C82 (I) and TmCN@C82 (II) were precisely characterized as TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, respectively, via single-crystal X-ray diffraction and through their co-crystalization with decapyrrylcorannulene (DPC) molecules, which enhance the crystallinity of EMFs [47]. Both co-crystals were found to crystallize in P21/c, a space group of No. 14, which is commonly seen in the EMF-DPC co-crystallization systems, and the utilization of the low-symmetry primitive lattice for the EMF-DPC co-crystals could effectively circumvent the “crystallographic mirror dilemma” that generally appears in the EMF-NiII(OEP) co-crystals crystalized in the C2/m space group [48]. As shown in Figure 2a,b, the TmCN@C82 isomers were co-crystallized with two DPC molecules, exhibiting a distinctive V-shaped configuration with a dihedral angle of about 65°. The closest C···C distances between both TmCN@C82 isomers and the DPC molecules were measured to be ~3.37 Å; this is close to the interlayer spacing observed in graphite (3.35 Å), suggesting their π–π stacking interactions.
The encapsulated TmCN cluster, with a CN non-metallic unit supported by a mono-metallic Tm ion, adopts a triangular configuration inside both C82 isomers, similar to their analogs MCN@Cs(6)-C82 and MCN@C2v(9)-C82 (M = Y, Tb, Dy, Lu). Due to the larger electronegativity of nitrogen versus carbon, the distance of the Tm-N bond is significantly shorter than that of the Tm-C bond, and the C-N bond lengths fall in the range of typical C-N triple bonds, as shown in Figure 2c,d. The encapsulated Tm ion shows some slight disorder which is probably caused by thermal vibration. The dominant Tm site, with the most significant occupancy, is located over an s-indacene-type hexagon of the carbon cages, exhibiting Tm-cage distances in the range of 2.23–2.49 Å and 2.23–2.68 Å inside the Cs(6)-C82 and C2v(9)-C82 carbon cages, respectively. Interestingly, the dominant Tm location is aligned with the symmetrical plane of both the Cs(6)-C82 and C2v(9)-C82 cages, which is in perfect agreement with the recent finding of the “mirror observation” for mono-metallofullerenes, suggesting that the mono-metallic cyanide clusterfullerenes display some structural characteristics that are similar to those of mono-metallofullerenes [48].
The crystallographic results suggest the preference of the TmCN cluster for encapsulation inside the cages of Cs(6)-C82 and C2v(9)-C82, which can be inferred from our previous work on TbCN@C82 isomers [32]. TbCN@C2v(9)-C82 is the most stable isomer among all TbCN@C82 isomers, followed by TbCN@Cs(6)-C82, which is similar to the relative energy order found for the YCN@C82 isomers. The results reveal that the cage cavity volumes of Cs(6)-C82 and C2v(9)-C82 are suitable for encapsulation of a metal cyanide cluster; this is in agreement with the theoretical studies on C84 isomers [49], which provided insights into the relationship between the stability of an encapsulated endo-unit and the volume of a specific carbon cage.
The electronic properties of TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 were investigated via visible-near infrared (Vis-NIR) spectroscopy. It is well-established that the absorption spectra of EMFs are primarily governed by the π–π* excitations of the carbon cages; thus, Vis-NIR spectroscopy is commonly employed to study the electronic structures of EMFs [12]. As shown in Figure 3, TmCN@Cs(6)-C82 exhibits a distinct spectrum with absorptions at 510, 758, 1016, 1134, and 1334 nm, while TmCN@C2v(9)-C82 displays a strong absorption at 1338 nm, accompanied by relatively weak absorptions at 524, 622, 706, 770, 1016, and 1168 nm. The measured optical bandgap of TmCN@Cs(6)-C82 is 0.76 V, slightly larger than that of TmCN@C2v(9)-C82 (0.71 V). The absorption features and optical bandgaps of both TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 resemble those of Y-, Tb-, Dy-, and Lu-CYCFs (Table 1) [31,32,33,34,35], which share the same cage isomerism and exhibit a divalent electronic configuration. Consequently, the formal electronic configurations of the two Tm-based CYCFs can be described as Tm3+(CN)−@(Cs(6)-C82)2− and Tm3+(CN)−@(C2v(9)-C82)2−, respectively. Notably, compared to TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, Tm@Cs(6)-C82 and Tm@C2v(9)-C82 display distinct absorption spectra [50,51,52] despite sharing the same cage isomerism. In addition, previous X-ray absorption spectroscopy (XAS) and ultraviolet photoelectron spectroscopy (UPS) studies [53,54] demonstrated that the Tm atoms prefer an oxidation state of +2 in mono-metallofullerenes. Therefore, the obtained results indicate that on one hand, the Tm ion or the TmCN cluster significantly contributes to the molecular orbitals. On the other hand, the higher oxidation state (+3) of the Tm atom in the TmCN cluster is identified due to bonding with the non-metallic CN unit.
Figure 4 shows the electrochemical behaviors of TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, determined using cyclic voltammetry (CV) with tetrabutylammonium hexafluorophosphate (TBAPF6) and ferrocene (Fc) as the supporting electrolyte and internal standard, respectively. Both show four reversible reduction steps and one reversible oxidation step, recorded as +0.55, −0.67, −0.90, −1.72, and −2.16 V for TmCN@Cs(6)-C82 and +0.64, −0.45, −0.79, −1.60, and −1.94 for Tm@C2v(9)-C82. The full reduction potentials of TmCN@Cs(6)-C82 are also more negatively shifted to about 0.1–0.2 V than those of Tm@C2v(9)-C82; thus, TmCN@Cs(6)-C82 is more accessible for oxidation than Tm@C2v(9)-C82. Notably, the electrochemical gap of TmCN@Cs(6)-C82 (1.22 V) is larger than that of Tm@C2v(9)-C82 (1.09 V), which results from the relatively more significant difference in their first reduction potentials.
The comparison of the two TmCN@C82 isomers and other mono-metallic EMFs based on Cs(6)-C82 and C2v(9)-C82 was also studied, as shown in Table 2. The redox behaviors of TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 are fairly similar to those of the corresponding Y-, Tb-, Dy-, and Lu-CYCF counterparts [31,32,33,34,35], suggesting that both TmCN@C82 isomers bear a divalent electronic configuration of Tm3+(CN)−@(Cs(6)-C82)2−, which is in agreement with the spectroscopic result. Similar redox behaviors between divalent M@C82 isomers, such as Yb@Cs(6)-C82 and Yb@C2v(9)-C82 [55] and TmCN@C82 isomers further confirm the electronic configurations of Tm3+(CN)−@(C82)2− for both Cs(6) and C2v(9) isomerisms. In comparison, trivalent mono-metallofullerenes (M3+)@(C82)3- (M = Y [56], La [57,58], Pr [59], Er [60], and U [61], etc.) based on Cs(6) and C2v(9) cage isomerism exhibit sharply different redox potentials with much more negatively shifted first oxidation potentials and much smaller electrochemical gaps. These phenomena originate from the three-electron charge transfer of (M3+)@(C82)3−, which results in an open-shell electronic structure, while TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 have a closed-shell electronic structures due to the two-electron transfer from the encapsulated TmCN cluster to the carbon cages.

3. Materials and Methods

Materials. The ragents used in this work were Tm2O3 (99.99%, Suzhou Rare Earth New Materials Co., Suzhou, China), TiO2 (99%, Sinopharm Chemical Reagent Co., Ltd., Ningbo, China), CS2 (99%, Sinopharm Chemical Reagent Co., Ltd.), toluene (99%, Sinopharm Chemical Reagent Co., Ltd.), tetrabutylammonium hexafluorophosphate (electrochemical-grade, Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China), 1,2-dichlorobenzene (99%, Shanghai Aladdin Biochemical Technology Co., Ltd.), and graphite rods and graphite powder (Sinosteel Shanghai New Graphite Material Co., Shanghai, China).
Synthesis of TmCN@C82 isomers. Soot containing TmCN@C82 isomers was synthesized using a modified Krätschmer–Huffman DC arc discharge method. Graphite rods packed with graphite powder, Tm2O3, and TiO2, with a C/Tm/Ti molar ratio of 15/1/1, were preheated in a tube furnace at 1000 °C for 20 h under a nitrogen atmosphere. Subsequently, the preheated graphite rods were installed in a VDK-250 arc discharge reactor (Beijing Technol Science Co., Ltd., Beijing, China) under a low-vacuum atmosphere with 200 mbar He and 10 mbar N2, followed by vaporization in a DC of 120 A. The two TmCN@C82 isomers were extracted from the carbon soot with CS2 using the Soxhlet extraction method. The resulting fullerene solution in CS2 was evaporated and then dissolved again in toluene, followed by concentration for the following multi-stage HPLC procedures [62,63].
Isolation of TmCN@C82 isomers. As illustrated in Figure 5, a four-stage HPLC process was employed to purify the two TmCN@C82 isomers, and toluene was employed as the eluent in all stages. The first stage was performed on a preparative 5PYE column (20 × 250 mm) with a 15 mL/min flow rate, and fraction A, which contained the two TmCN@C82 isomers and other fullerenes, was collected, concentrated, and then re-injected into the HPLC. In the second stage, a recycling mode was employed on a preparative Buckyprep-M column (20 × 250 mm) with a 12 mL/min flow rate. After three runs of recycling, fraction A-4, which contained the TmCN@C82 isomers, was collected for the next stage. A semi-preparative 5PBB column (10 × 250 mm, 4 mL/min flow rate) was used in the third separation stage to remove the other mixed fullerenes in the A-4 fraction. Fraction A-4-3 was found to contain only two TmCN@C82 isomers, and all the impurity fullerenes had been removed. In the last stage, a recycling HPLC process was employed to purify the two isomers, using a semi-preparative Buckyprep column (10 × 250 mm) with a 4 mL/min flow rate. After 13 recycling runs, purified TmCN@Cs(6)-C82, labeled as A-4-3-1, and TmCN@C2v(9)-C82, labeled as A-4-3-2, were individually collected for further characterizations. The detailed fraction information for each stage is shown in Table 3.
Spectroscopic studies. The mass spectra of the two TmCN@C82 isomers were recorded on an Autoflex III matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS, Bruker, Germany) under positive mode. The Vis-NIR spectra of the purified samples were measured using a UV-3600 spectrometer (Shimadzu, Japan).
Electrochemical analysis. The electrochemical study was performed in a CHI 660 potentiostat (CH Instrument, USA) using a three-electrode system, including a glassy carbon working electrode, a platinum (Pt) wire counter electrode, and a silver (Ag) wire reference electrode. Tetrabutylammonium hexafluorophosphate (TBAPF6) and ferrocene (Fc) were employed as the supporting electrolyte and the internal standard, respectively. TBAPF6, Fc, and the samples were all dissolved in 1,2-dichlorobenzene (o-DCB).
X-ray crystallographic study. The co-crystals of the DPC molecules and EMF samples were obtained by slowly laying a DPC toluene solution onto an EMF CS2 solution in a nuclear magnetic resonance (NMR) tube. Black block co-crystals of a suitable size for X-ray diffraction analysis were observed on the wall or in the bottom after 10–15 days. The crystallographic data were collected in the BL17B beamline station at Shanghai Synchrotron Radiation Facility. The crystallographic structures were solved using SHELXT-2014 via the intrinsic phasing method and then refined with SHELXL-2018 via the full-matrix least-squares method based on F2 within the software Olex2 [64,65]. The SQUEEZE program [66] included in the PLATON program was employed to calculate the contribution of the disordered toluene solvents. The detailed crystallographic data of the two co-crystals are shown in Table 4.

4. Conclusions

In conclusion, we report the synthesis, isolation, and characterization of the first Tm-based CYCFs with the popular C82 carbon cages via mass spectrometry, single-crystal X-ray crystallography, UV-vis-NIR spectroscopy, and cyclic voltammetry. The molecular structures of these two TmCN@C82 were unambiguously determined to be TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82. The TmCN cluster bears a popular triangular configuration, and the Tm ion is located in one symmetrical plane of the carbon cage for both Cs(6)-C82 and C2v(9)-C82. In addition, the two TmCN@C82 isomers feature the characteristic spectral and electrochemical properties of divalent EMFs, suggesting a closed-shell electronic structure described as Tm3+(CN)−@(C82)2−. Compared to the Tm@C82 isomers, which contain a divalent Tm2+ ion, the 3+ oxidation state of the Tm atom in the mono-metallic TmCN cluster is identified due to bonding with the encapsulated cyanide anion.

Author Contributions

Conceptualization, S.Y.; funding acquisition, Y.-R.Y. and S.Y.; investigation, H.Z., J.X., H.J., and W.X.; project administration, S.Y.; supervision, Y.-R.Y. and S.Y.; writing—original draft, H.Z. and Y.-R.Y.; writing—review and editing, M.C., Y.-R.Y. and S.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (51925206 and U1932214) and the Fundamental Research Funds for the Central Universities (WK2060000051).

Data Availability Statement

The crystallographic data can be obtained free of charge from the Cambridge Crystallographic Data Centre with the CCDC numbers 2253745 and 2253746 via www.ccdc.cam.ac.uk/data_request/cif (accessed on 31 August 2022). The other data are available upon reasonable request from the corresponding authors.

Acknowledgments

We thank the staff in the BL17B beamline of the National Facility for Protein Science Shanghai (NFPS) at the Shanghai Synchrotron Radiation Facility for their assistance during the crystallographic data collection.

Conflicts of Interest

The authors declare no conflict of interest.

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Inorganics 11 00323 g001 550
Figure 1. HPLC chromatograms of purified (a) TmCN@C82 (I) and (b) TmCN@C82 (II), obtained using an analytical Buckyprep column with toluene as the eluent and a flow rate of 1 mL/min. The inserts show the mass spectra of two TmCN@C82 isomers with experimental versus theoretical isotopic distributions.
Figure 1. HPLC chromatograms of purified (a) TmCN@C82 (I) and (b) TmCN@C82 (II), obtained using an analytical Buckyprep column with toluene as the eluent and a flow rate of 1 mL/min. The inserts show the mass spectra of two TmCN@C82 isomers with experimental versus theoretical isotopic distributions.
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Inorganics 11 00323 g002 550
Figure 2. Oak Ridge thermal ellipsoid plot (ORTEP) drawings of crystallographic structures of the two co-crystals. (a,b) The relative orientations between two DPC molecules and (a) TmCN@Cs(6)-C82 and (b) TmCN@C2v(9)-C82. (c,d) The relative orientations between the encapsulated TmCN cluster with detailed structural information and the (c) Cs(6)-C82 and (d) C2v(9)-C82 cages. The Tm, N, and C atoms are presented as green, blue, and gray, respectively.
Figure 2. Oak Ridge thermal ellipsoid plot (ORTEP) drawings of crystallographic structures of the two co-crystals. (a,b) The relative orientations between two DPC molecules and (a) TmCN@Cs(6)-C82 and (b) TmCN@C2v(9)-C82. (c,d) The relative orientations between the encapsulated TmCN cluster with detailed structural information and the (c) Cs(6)-C82 and (d) C2v(9)-C82 cages. The Tm, N, and C atoms are presented as green, blue, and gray, respectively.
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Inorganics 11 00323 g003 550
Figure 3. The Vis-NIR absorption spectra of TmCN@Cs(6)-C82 (in blue) and TmCN@C2v(9)-C82 (in red). The inserts are photographs of the two CYCFs dissolved in CS2. The spectra of the two TmCN@C82 isomers are shown together by shifting one along the ordinate axis, and the absorption peaks are indicated by black arrows.
Figure 3. The Vis-NIR absorption spectra of TmCN@Cs(6)-C82 (in blue) and TmCN@C2v(9)-C82 (in red). The inserts are photographs of the two CYCFs dissolved in CS2. The spectra of the two TmCN@C82 isomers are shown together by shifting one along the ordinate axis, and the absorption peaks are indicated by black arrows.
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Inorganics 11 00323 g004 550
Figure 4. Cyclic voltammograms of (a) TmCN@Cs(6)-C82 and (b) TmCN@C2v(9)-C82 in a o-DCB solution with a scan rate of 100 mV·s−1. TBAPF6 and Fc were employed as the internal standard and supporting electrolyte, respectively. Black circles and asterisks are presented to show the redox and the Fc/Fc+ peaks.
Figure 4. Cyclic voltammograms of (a) TmCN@Cs(6)-C82 and (b) TmCN@C2v(9)-C82 in a o-DCB solution with a scan rate of 100 mV·s−1. TBAPF6 and Fc were employed as the internal standard and supporting electrolyte, respectively. Black circles and asterisks are presented to show the redox and the Fc/Fc+ peaks.
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Inorganics 11 00323 g005 550
Figure 5. HPLC isolation procedure for TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82. (a) the first stage of HPLC isolation procedure on a preparative 5PYE column (20 × 250 mm). (b) the second stage of HPLC isolation procedure on a preparative Buckyprep-M column (20 × 250 mm). (c) the third stage of HPLC isolation procedure on a semi-preparative 5PBB column (10 × 250 mm). (d) the fourth stage of HPLC isolation procedure on a semi-preparative Buckyprep column (10 × 250 mm). The insert in (d) shows the recycled fractions of A-4-3-1 (red) and A-4-3-2 (blue), which represent the purified TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, respectively.
Figure 5. HPLC isolation procedure for TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82. (a) the first stage of HPLC isolation procedure on a preparative 5PYE column (20 × 250 mm). (b) the second stage of HPLC isolation procedure on a preparative Buckyprep-M column (20 × 250 mm). (c) the third stage of HPLC isolation procedure on a semi-preparative 5PBB column (10 × 250 mm). (d) the fourth stage of HPLC isolation procedure on a semi-preparative Buckyprep column (10 × 250 mm). The insert in (d) shows the recycled fractions of A-4-3-1 (red) and A-4-3-2 (blue), which represent the purified TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82, respectively.
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Table
Table 1. Vis-NIR absorption spectral data of two TmCN@C82 isomers as well as Y-, Tb-, Dy-, and Lu-CYCFs for comparison.
Table 1. Vis-NIR absorption spectral data of two TmCN@C82 isomers as well as Y-, Tb-, Dy-, and Lu-CYCFs for comparison.
CompoundsAbsorption Peaks (nm)λonset (nm)ΔEgap (eV) 1Note
TmCN@Cs(6)-C82510, 758, 1016, 1134, 133416240.76this work
TbCN@Cs(6)-C82491, 744, 1072, 1132, 131816200.77Ref [32]
DyCN@Cs(6)-C82497, 744, 1024, 1140, 133916560.75Ref [33]
LuCN@Cs(6)-C82494,596, 744, 1069, 1131, 134516380.76Ref [35]
YCN@Cs(6)-C82491, 741,1064, 1123, 131816200.77Ref [31]
TmCN@C2v(9)-C82524, 622, 706, 770, 1016, 1168, 133817400.71This work
TbCN@C2v(9)-C82518, 618, 710, 772, 1144, 132017700.70Ref [32]
DyCN@C2v(9)-C82536, 627, 1144, 134217850.69Ref [33]
LuCN@C2v(9)-C82512, 621, 697, 782, 1096, 129616800.74Ref [35]
1 ΔEgap = 1240/λonset.
Table
Table 2. Redox potentials (V vs. Fc/Fc+) and electrochemical gaps of TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 and the corresponding cyanide metallofullerenes MCN@C82 and mono-metallofullerene M@C82 isomers.
Table 2. Redox potentials (V vs. Fc/Fc+) and electrochemical gaps of TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82 and the corresponding cyanide metallofullerenes MCN@C82 and mono-metallofullerene M@C82 isomers.
CompoundsoxE1redE1redE2redE3redE4ΔEgap (eV) Note
TmCN@Cs(6)-C820.55−0.67−0.90−1.72−2.161.22This work
TbCN@Cs(6)-C820.55−0.59−0.84−1.77−1.921.14Ref [32]
DyCN@Cs(6)-C820.56−0.58−0.841.77−1.921.14Ref [33]
LuCN@Cs(6)-C820.52−0.58−0.90−1.69−1.861.10Ref [35]
YCN@Cs(6)-C820.56−0.59−0.84−1.76−1.921.15Ref [31]
La@Cs(6)-C82−0.07−0.47−1.40−2.01−2.400.40Ref [57]
Pr@Cs(6)-C82−0.07−0.48−1.39−1.99/0.41Ref [59]
Er@Cs(6)-C82−0.09−0.44−1.46−2.04−2.460.35Ref [60]
Y@Cs(6)-C82−0.07−0.43−1.43−2.05/0.36Ref [56]
Yb@Cs(6)-C820.34−0.62−0.92−1.81−2.010.94Ref [55]
TmCN@C2v(9)-C820.64−0.45−0.79−1.60−1.941.09This work
TbCN@C2v(9)-C820.55−0.46−0.81−1.78−1.961.01Ref [32]
DyCN@C2v(9)-C820.56−0.45−0.81−1.78−1.961.01Ref [33]
LuCN@C2v(9)-C820.50−0.54−0.96−1.71−1.931.04Ref [35]
La@C2v(9)-C820.07−0.42−1.37−1.53−2.260.49Ref [58]
Pr@C2v(9)-C820.07−0.39−1.35−1.46−2.210.46Ref [59]
Er@C2v(9)-C820.08−0.42−1.40−2.18/0.50Ref [60]
U@C2v(9)-C820.10−0.43−1.42−1.76−1.770.53Ref [61]
Y@C2v(9)-C820.10−0.34−1.34−2.22/0.44Ref [56]
Yb@C2v(9)-C820.61−0.46−0.78−1.60−1.901.07Ref [55]
Table
Table 3. The major eluted components in each HPLC fraction and their relative abundances.
Table 3. The major eluted components in each HPLC fraction and their relative abundances.
FractionSubfractionMajor ComponentRelative Abundance
AA-1C84–8646.1%
A-2Tm@C82/TmC77N3.4%
A-3Tm@C80–84/TmC83N36.7%
A-4Tm@C80,84/Ti2C80/TmCN@C8213.8%
A-4A-4-1Ti2C802.2%
A-4-2Tm@C806.5%
A-4-3TmCN@C82 (Cs(6), C2v(9))8.7%
A-4-1Tm@C8482.6%
A-4-3A-4-3-1TmCN@Cs(6)-C8252.1%
A-4-3-2TmCN@C2v(9)-C8247.9%
Table
Table 4. Crystallographic information of two TmCN@C82 co-crystals.
Table 4. Crystallographic information of two TmCN@C82 co-crystals.
CrystalTmCN@Cs(6)-C82TmCN@C2v(9)-C82
Empirical formulaC210H88N21TmC210H88N21Tm
Formula weight3073.943073.94
HabitBlockBlock
Temperature, K100100
Crystal systemMonoclinicMonoclinic
Space groupP21/cP21/c
a, Å14.66914.724
b, Å32.14632.032
c, Å32.21332.215
α, deg9090
β, deg101.74101.91
γ, deg9090
Volume, Å314,872.314,866.8
Z44
Dx, g/cm31.3731.373
F(000)62566256
Crystal Size, mm30.06 × 0.03 × 0.010.12 × 0.08 × 0.03
2θ max, °20.49924.712
R1/wR2 (I > 2σ(I)) 10.1193/0.28310.0937/0.2531
GOF1.1161.052
Completeness0.9720.987
Obs reflects575214,863
Total reflects14,47825,026
Parameters21312162
metal disorderTm1(0.60)/Tm2(0.08)/Tm3(0.17)/
Tm4(0.11)/Tm5(0.04)		Tm1(0.25)/Tm2(0.14)/Tm3(0.09)/Tm4(0.04)/Tm5(0.08)/Tm6(0.13)/
Tm7(0.20)/Tm8(0.07)
1R1 = ∑||Fo| − |Fc||/∑|Fo|, wR2 = [∑w(Fo2 − Fc2)2]/∑w(Fo2)2]1/2.
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MDPI and ACS Style

Zhang, H.; Xin, J.; Jin, H.; Xiang, W.; Chen, M.; Yao, Y.-R.; Yang, S. TmCN@C82: Monometallic Clusterfullerene Encapsulating a Tm3+ Ion. Inorganics 2023, 11, 323. https://doi.org/10.3390/inorganics11080323

AMA Style

Zhang H, Xin J, Jin H, Xiang W, Chen M, Yao Y-R, Yang S. TmCN@C82: Monometallic Clusterfullerene Encapsulating a Tm3+ Ion. Inorganics. 2023; 11(8):323. https://doi.org/10.3390/inorganics11080323

Chicago/Turabian Style

Zhang, Huichao, Jinpeng Xin, Huaimin Jin, Wenhao Xiang, Muqing Chen, Yang-Rong Yao, and Shangfeng Yang. 2023. "TmCN@C82: Monometallic Clusterfullerene Encapsulating a Tm3+ Ion" Inorganics 11, no. 8: 323. https://doi.org/10.3390/inorganics11080323

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