Steering the Geometry of Butterfly-Shaped Dimetal Carbide Cluster. within a Carbon Cage via Trifluoromethylation of Y 2 C 82 (6)

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1 Supporting Information for: Steering the Geometry of Butterfly-Shaped Dimetal Carbide Cluster within a Carbon Cage via Trifluoromethylation of Y 2 C 82 (6) Fei Jin, a Nadezhda B. Tamm, b Sergey I. Troyanov, b and Shangfeng Yang* a a Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei , China b Department of Chemistry, Moscow State University, Moscow , Leninskie gory, Russia S1. Synthesis and isolation of Y 2 C 82. Y 2 C 82 was synthesized by a modified Krätschmer-Huffman DC-arc discharge method using a mixture of Y 2 O 3, TiO 2 and graphite (molar ratio of Y/Ti/C = 1:1:15) as the raw material under conditions of 400 mbar He mixed with 10 mbar N 2 as reported previously in ref. [S1]. The extracted mixture was subjected to HPLC separation in toluene using a preparative mm 5PYE column. Fraction A eluted at min containing Y 2 C 82 (Figures S1(I)) was collected for further isolation by multi-step HPLC as reported previously in ref. [S1]. Briefly, in the first-step recycling HPLC isolation running with a preparative mm 5PYE column, four fractions were collected after three cycles (Figure S2(II)). The collected subfraction A-1 (mainly containing Y 2 C 82, Y@C 82 and YCN@C 84 ) was then subjected to the second-step HPLC running with a mm Buckyprep-M column, resulting in the collection of four fractions, A-1-1, A-1-2, A-1-3, and A-1-4 (Figure S2(III)). Subfraction A-1-3 was collected for the third-step recycling HPLC running with a preparative mm Buckyprep column. After eleven cycles, subfraction A was collected which contains Y 2 C 82 and YCN@C 84 with roughly equal amounts according to MALDI-TOF mass spectroscopic measurements (Figure S2). We attempted to purify Y 2 C 82 from this fraction by recycling HPLC, but found that the purification was too tedious and resulted in loss of material after multiple cycles, thus this fraction as a hardly separable mixture was used for trifluoromethylation experiments. S1

2 Figure S1. Isolation scheme of fraction A. (I) HPLC profile of the extract mixture obtained by a modified arcdischarge synthesis ( mm 5PYE column; flow rate 15.0 ml/min; injection volume 15 ml; toluene as eluent; 40 C). (II) Recycling HPLC profile of subfraction A ( mm 5PYE column; flow rate 15.0 ml/min; injection volume 15 ml; toluene as eluent; 40 C). Fraction A-2 mainly contains Y@C 82, fractions A-3 and A-4 mainly contain C 88 and Y@C 82, respectively. (III) The next step recycling HPLC isolation of subfraction A-1 ( mm Buckyprep-M column; flow rate 5.0 ml/min; injection volume 5 ml; toluene as eluent; 40 C). Fraction A-1-1 mainly contains C 86, fraction A-1-2 mainly contains C 86 and YCN@C 82, and fraction A-1-4 mainly contains Y@C 82. (IV) Fraction A-1-3 was isolated by recycling HPLC ( mm Buckyprep column; flow rate 15.0 ml/min; injection volume 15 ml; toluene as eluent; 40 C) and fraction A contains Y 2 C 82 and YCN@C 84. S2

3 Figure S2. MALDI-TOF mass spectra of subfraction A S2. Synthesis, isolation and characterization of Y 2 C 82 (CF 3 ) 16. Trifluoromethylation of subfraction A as a hardly separable mixture of Y 2 C 82 and YCN@C 84 was carried out with CF 3 I in quartz ampoules at 450 ºC for 2h as described in ref. [S1]. The trifluoromethylated product was analyzed by MALDI-TOF mass spectrometry, showing the presence of compounds of only three compositions, Y 2 C 82 (CF 3 ) 16 (m/z=2290), YCN@C 84 (CF 3 ) 16 (m/z=2227) and YCN@C 84 (CF 3 ) 18 (m/z=2365) (Figure S3). Figure S3. MALDI-TOF mass spectrum of the trifluoromethylated product of subfraction A S3

4 The trifluoromethylated product was dissolved in n-hexane and subjected to HPLC separation using a semipreparative Buckyprep column ( mm, Nacalai Tesque Inc.) and n-hexane as the eluent at a flow rate of 2.3 ml min 1. A total of 37 fractions was collected with elution times in the range of 6-70 min (Figure S4). In addition to the fractions eluted at 9.2, 13.2, and 66.6 min (labeled as YCN/16-(I-III)) assigned to three isomers of YCN@C 84 (CF 3 ) 16 and the fraction eluted at 34.4 min (labeled as YCN/18-I) correlated to YCN@C 84 (CF 3 ) 18, S1 four fractions eluted at 9.7, 11.6, 20.7, and 50.1 min (labeled as Y 2 C 2 /16-(I-IV)) showed similar compositions with the prevailing mass number of Y 2 C 82 (CF 3 ) 16 ( m/z = 2290) (Figure S5). Slow evaporation or recrystallization of fractions Y 2 C 2 /16-(I-IV) from different solvents (n-hexane, toluene, p-xylene) gave crystals suitable for single-crystal XRD study with the use of synchrotron radiation, revealing their molecular structures as four isomers of Y 2 C 82 (6)(CF 3 ) 16 numbered I IV according to their increasing elution times (Figure S4). Figure S4. HPLC profile of trifluoromethylated product in n-hexane. Four fractions eluted at 9.7, 11.6, 20.7, and 50.1 min are assigned to four isomers of Y 2 C 82 (CF 3 ) 16 (labeled as Y 2 C 2 /16-(I-IV)). Fractions labeled as YCN/16-(I-III) eluted at 9.2, 13.2, and 66.6 min mark three isomers of YCN@C 84 (CF 3 ) 16, and a fraction labeled as YCN/18-1 marks YCN@C 84 (CF 3 ) 18 reported previously in ref. [S1]. S4

5 Fraction Y 2 C 2 /16-I Fraction Y 2 C 2 /16-II Fraction Y 2 C 2 /16-III Fraction Y 2 C 2 /16-IV Figure S5. MALDI-TOF mass spectra of fractions Y 2 C 2 /16-(I-IV) showing the prevailing mass number of 2290 corresponding to Y 2 C 82 (CF 3 ) 16. Some weak additional peaks refer to mono- and dihydroxides such as Y 2 C 82 (CF 3 ) 16 OH and Y 2 C 82 (CF 3 ) 16 (OH) 2. The spectrum of fraction Y 2 C 2 /16-I contains a small peak at m/z=2227 corresponding to an admixture of YCN@C 84 (CF 3 ) 16. profile of trifluoromethylated product in n-hexane. S3. Geometric data of the encapsulated Y 2 C 2 cluster within C s -C 82 (6) carbon cage. Table S1 shows selected data on geometry of the encapsulated Y 2 C 2 cluster within the trifluoromethylated C s -C 82 (6) carbon cage according to the results of X-ray crystallography. ESD s of Y C and C C bonds are around 0.01 and Å, respectively, whereas Y Y distances have esd s of Å. Table S1. Geometric data of the encapsulated Y 2 C 2 cluster within Y 2 C 82 (6)(CF 3 ) 16 (I-IV). Y-C bonds Y-C (cage), Y1CC/Y2CC dihedral Isomer C-C bond (Å) Y1 Y2 (Å) (Y 2 C 2 ) (Å) (Å) angle ( ) I II [a] III IV [a] Two crystallographically independent Y 2 C 82 (6)(CF 3 ) 16 molecules are present in the crystal structure. References [S1] Jin, F.; Wang, S.; Tamm, N. B.; Yang, S.; Troyanov, S. I. Angew. Chem. Int. Ed. 2017, 56, S5