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1 DOI: /NCHEM.1748 A missing link in the transformation from asymmetric to symmetric metallofullerene cages implies a top-down fullerene formation mechanism Jianyuan Zhang, Faye L. Bowles, Daniel W. Bearden, W. Keith Ray, Tim Fuhrer, Youqing Ye, Caitlyn Dixon, Kim Harich, Richard, F. Helm, Marilyn M. Olmstead *, Alan L. Balch * and Harry C. Dorn * Supplementary Methods Isolation of Y 2 C 1 (51383)-C 84 and Gd 2 C 1 (51383)-C 84. The soot containing 13 C enriched fullerenes and yttrium metallofullerenes was extracted with o-xylene. The resulting solution was stirred with cyclopentadiene functionalized silica (~1g per 100 ml solution) for 12 hours and then filtered. The filtrate was treated by the same cyclopentadiene method for one more time, and then was loaded onto HPLC for separation. The first stage was performed on a 5 cm-diameter PBB column (Figure S1) and 8 fractions, named as Y-1 to Y-8, were collected. The major components for these 8 fractions are C 84 and Y 79 N, Y 3 N@C 80, Y 3 N@C 82, Y 3 N@C 84, Y 3 N@C 86, Y 3 N@C 88, Y 2 C 92, and larger fullerene and metallofullerenes, respectively. 1 Y 2 C 1 (51383)-C 84 was co-eluted with Y 3 N@C 82 in the Y-3 fraction. The Y-3 fraction was injected onto a 1 cm-diameter PYE column for second stage separation (Figure S2). Y 2 C 1 (51383)-C 84 has a retention time of 78 minutes, which is very different from other members in the Y-3 fraction. The amount of Y 2 C 1 (51383)-C 84 is about 22% compared to the previously reported Y 3 N@C Further chromatographic purification was performed to give the purified Y 2 C 1 (51383)-C 84 (Figure S3). The soot containing fullerenes and gadolinium metallofullerenes was extracted with o-xylene. The resulting solution was subject to extensive cyclopentadiene functionalized silica treatment until all empty cage fullerenes were removed, and the filtrate was loaded onto HPLC for separation. The first stage was performed on a 5 cm-diameter PBB column (Figure S4) and 8 fractions, named as Gd-1 to Gd-8, were collected. The major components of these 8 fractions are Gd 79 N, Gd 3 N@C 80, Gd 3 N@C 82, Gd 3 N@C 84, Gd 3 N@C 86, Gd 3 N@C 88, Gd 2 C 92, and larger fullerene and metallofullerenes, respectively. Gd 2 C 1 (51383)-C 84 was co-eluted with Gd 3 N@C 82 in the Gd-3 fraction. The Gd-3 fraction was injected onto a 1 cm-diameter PYE column for second stage separation (Figure S5). Gd 2 C 1 (51383)-C 84 has a retention time of 78 minutes, which is very different from most other members in the Gd-3 fraction. The amount of Gd 2 C 1 (51383)-C 84 is about 37% compared to the previously reported Gd 3 N@C Further chromatographic purification was performed to give the purified Gd 2 C 1 (51383)-C 84 (Figure S6). Mass-spectrometry method: Low resolution mass-spectral data (Fig. S3, S6 insets) were laser desorption/ionization time-of-flight spectra obtained on a Kratos SEQ instrument without matrix. NATURE CHEMISTRY 1

2 High resolution mass-spectral data (Fig. 4, S11, S13, S14) were laser desorption/ionization timeof-flight spectra obtained on an AB Sciex 4800 MALDI TOF instrument without matrix. To investigate the isotopic distribution of fullerenes and metallofullerenes (Fig. 4, S13, S14), 60% laser power was used. For the laser ablation experiment of Gd 2 C 1 (51383)-C 84 (Fig. S11), 60% and full laser power was used, respectively. Crystallographic solution of Gd 2 C 1 (51383)-C 84 Ni(OEP) 1.75(toluene) 0.25(benzene): The initial solution revealed a molecule of Ni(OEP), disordered sites of toluene/benzene and three Gd positions. One orientation for a C 84 cage, and disordered encapsulated Gd 2 C 2, were found by repeated cycles of least-squares refinement and difference Fourier maps. At least one more orientation was clearly present. Since the cage was found to have C 1 symmetry, a second orientation of opposite hand was eventually placed by successive difference maps and refinement of inverted C 1 (51383)-C 84 rigid groups. Each enantiomer was assigned 0.5 occupancy. In the final cycles of refinement, in order to reduce correlation effects and achieve convergence, the carbons of the ball were freely refined but kept isotropic. A SIMU command was applied to smooth the displacement parameters. Some carbons were refined with equal isotropic thermal parameters due to similar positions and high correlations. In addition, a loose distance restraint of 1.429(15) Å was applied to C-C all distances except for the C-C bond of the adjoined pentagons which was restrained to 1.410(15) Å. The structure also shows disorder in the Gd sites. The final model included eighteen Gd positions. Gd1 and Gd10 are the predominant sites on opposite sides of the C 2 group, with occupancies of 0.52 and 0.34, respectively. Gd2 Gd9 have occupancies of 0.11, 0.11, 0.08, 0.05, , 0.03, 0.03, while Gd11 Gd18 have occupancies of 0.25, 0.20, 0.06, 0.05, 0.02, 0.03, 0.03, 0.02, respectively. The total occupancy for all Gd positions in the asymmetric unit is 2.0. Initial site occupancies were refined, and they were fixed in the final cycles of refinement. All except Gd16, Gd17, and Gd18 were allowed to become anisotropic. There is some disorder in the carbide: C85 and C86 are the major positions at 0.75 occupancy each.; C86B is an alternative position at 0.50 occupancy. There are two solvate sites. One is occupied by overlapping toluene molecules at equal occupancy while the other contains 0.75 toluene and 0.25 benzene. These molecules were refined as rigid groups of idealized geometry. The numbering scheme was chosen to match that of the structure of Y 2 C 1 (51383)-C 84. Crystal data: C 86 Gd 2 C 36 H 44 N 4 Ni 1.75(C 7 H 8 ) 0.25(C 6 H 6 ), M w = , monoclinic, P2 1 /c, a = (7) Å, b = (5) Å, c = Å, β = (2), V = (5) Å3, Z = 4, R1 [18147 reflections with I > 2σ(I)] = 0.115, wr2 (all data) = 0.329, 1353 parameters, 511 restraints. A.cif file is available as supplementary data file with this manuscript. Explanation for A- and B- level alerts in the check cif routine: Alerts regarding Gd atoms: The Gd atoms are involved in primarily ionic bonding and the cif reports the distances as unusual. Alerts regarding Ni atoms: The positive residual density is 0.13 Å from Ni and is likely due to truncation errors, or to thermal motion, but its origin is unknown. NATURE CHEMISTRY 2

3 Supplementary Discussion Single-crystal results of Gd 2 C 1 (51383)-C 84. The asymmetric unit contains sites of one endohedral fullerene, one porphyrin, and two solvate molecules. There is no crystallographic symmetry. The solvate sites are orientationally disordered and shared between toluene and benzene. As depicted in a packing diagram, Fig. S10, the octaethyl groups of Ni(OEP) host the fullerene. In the figure, disorder is removed for clarity and only one enantiomer is shown. The shortest contacts between Ni1 and the fullerene cages are Ni1-C38, 2.92(3) Å and Ni1-C44B ( B refers to the enantiomer), 2.89(3) Å. The back-to-back porphyrin arrangement brings the inversion-related Ni1 Ni1 contact to 3.477(2) Å. Figure 2d shows the major Gd and carbide sites in the C 1 -C 84 cage. The closest Gd C contacts between Gd1 and Gd10 in C 1 -C 84 are depicted again in Figure 2d as viewed end-on. Similar contacts in C1B-C84B occur using Gd1 and Gd11. The distance between the centroid of the 5:5 C41-C42 bond and the centroid of the opposing hexagon is Å. The Gd 2 C 2 unit is asymmetrically placed along this span of the C 84 cage. While distances between Gd1 and the pentalene are shorter than those between Gd10 and the hexagon, distances between Gd1 and the carbide are longer than those between Gd10 and the carbide. In the major site shown, C85-C86, the carbide distance is 1.230(14) Å; in the minor site, C85-C86B, it is 1.327(19) Å. Consideration of the butterfly of Gd1-C85-C86-Gd10 yields a dihedral angle between the two GdC 2 planes of and the alternative Gd1-C85-C86B-Gd11 yields Supplementary Figures. Fig. S1. First-stage HPLC separation of 13 C enriched fullerenes and yttrium metallofullerenes on a 5 cm-diameter PBB column at room temperature, using toluene as eluent at 24 ml/min. NATURE CHEMISTRY 3

4 Fig. S2. HPLC separation of the Y-3 fraction on a 1 cm-diameter PYE column at room temperature, using toluene as eluent at 2 ml/min. Fig. S3. HPLC and mass-spectrum of 13 C enriched Y 2 C 1 (51383)-C 84. Fig. S4 First-stage HPLC separation of gadolinium metallofullerenes on a 5 cm-diameter PBB column at room temperature, using toluene as eluent at 24 ml/min. NATURE CHEMISTRY 4

5 Fig. S5. HPLC separation of the Gd-3 fraction on a 1 cm-diameter PYE column at room temperature, using toluene as eluent at 2 ml/min. Fig. S6. HPLC and mass-spectrum of Gd 2 C 1 (51383)-C 84. NATURE CHEMISTRY 5

6 Fig. S7. Stacked UV-vis spectra of M 2 C 1 (51383)-C 84 (M=Y, Gd) in toluene solution. Fig. S8. Full 13 C NMR spectrum for Y 2 C 1 (51383)-C 84. Fig. S9. Expanded region of 13 C NMR spectrum for the cluster signal of Y 2 C 1 (51383)-C 84 (left) in comparison of that of Y 2 C 3v (8)-C 82. NATURE CHEMISTRY 6

7 Fig. S10. Packing of the metallofullerene cage and disorder of the encapsulated gadolinium atoms revealed by single-crystal study. Top: A view of the packing of Gd 2 C 1 (51383)- C 84 Ni(OEP) 2(toluene) with disorder omitted for clarity. Bottom: A depiction of the disordered Gd positions inside the two enantiomers, A and B, in the crystal structure of Gd2C2@C1(51383)- C84. Due to the low occupancy of many of the positions and the near superposition of the two balls, the exact assignment of Gd to enantiomer is ambiguous. In A, the carbide is shown as comprised of C85 and C86 whereas in B, it is C85 and C86B. NATURE CHEMISTRY 7

8 Fig. S11. Laser desorption/ionization time-of-flight spectrum of Gd 2 C 1 (51383)-C 84 under different power level. Left: 60% power. Right: full power. Fig. S12. Interconversion map of C 1 (51383)-C 84 (this work), C s (51365)-C 84,(27) C s (6)-C 82,(23) and C 2v (9)-C 82.(23) NATURE CHEMISTRY 8

9 Fig. S13. Experimental (top) and theoretically simulated (bottom) mass-spectral isotopical distribution for empty cage fullerenes C 60, C 70 and C 84. The 13 C content for C 60, C 70 and C 84 was determined to be 9.7%, 9.8% and 9.4% in mol%, respectively, from the experimental isotopic distribution. Fig. S14. Experimental and theoretically simulated mass-spectral isotopical distribution for metallofullerenes Y 2 C 84 (isomeric mixture of Y 2 C 82 in Y-2 fraction as shown Fig. S1), and Y 2 C 86 (Y 2 C 84 in Y-3 fraction as shown Fig. S1, S2). The 13 C content for Y 2 C 84, and Y 2 C 86 was determined to be 10.5%, 10.2% in mol%, respectively, from the experimental isotopic distribution. NATURE CHEMISTRY 9

10 Fig. S15. DFT computation based relative concentration of the C 82 isomers with different charges as a function of temperature. Supplementary Tables Table S1 Isotopic distribution list of empty cage fullerene C 84. Average 13 C content = 9.4% NATURE CHEMISTRY 10

11 Table S2 Isotopic distribution list of metallofullerene Y 2 C 84. Average 13 C content = 10.6% Table S3 List of metallofullerenes involved in the pathways shown Figure 3 and Figure S12 with references. cage isomer C 1 (51383)-C 84 C s (51365)-C 84 C s (39663)-C 82 C s (6)-C 82 C 2v (9)-C 82 molecule M 2 C 84, M=Y, Gd (this work) M 3 N@C 84, M=Tb, a Tm, b Gd, b Y c M 3 N@C 82, M=Gd, d Y c M 2 C 82, M=Sc, e Y, f Er, g ErY, h Dy; i M@C 82, M=Ca, j Tm, k Yb, l Eu, m Sm, n La; o Er 82, p Sc 2 S@C 82, q Sc 2 O@C 82, r M 2 C 82, M=Sc, s Y, f Er, g Dy; i M@C 82, M=Ca, j Tm, k Yb, l Eu, m Sm, n Sc, t La, u Y, v Ce, w Gd, x Dy; y M 82, M=Er, g Tm, z TmHo z C 3v (8)-C 82 M 2 C 82, M=Sc, aa Y, f Er, g ErY, ab Dy, i M 82, M=Er, ac Sc, ad Y, f Tm, z TmHo; z M 2 S@C 82, M=Sc, q Y, ae Lu, ae Dy ae I h (7)-C 80 M 3 N@C 80, M=Sc, af Y, c Gd, ag Lu, ah Dy, ai Tm, aj Tb, ak mixed metals; M 80, M=La, al Ce; am Sc 3 CH@C 80, an Sc 4 O 80, ao Sc 4 O 80, ap Sc 3 C 80, aq ar Sc 3 CN@C 80 D 5h (6)-C 80 M 3 N@C 80, M=Sc, as Y, c Tm, aj Tb, ak at mixed metals; Ce 80 a Beavers et al. J. Am. Chem. Soc. 128, (2008); b Zuo et al. Chem. Commun (2008); c Fu et al. J. Am. Chem. Soc. 131, (2009); d Mercado et al. J. Am. Chem. Soc. 130, 7854 (2008); e Lu et al. J. Am. Chem. Soc. 133, (2011); f Inoue et al. J. Phys. Chem. B 108, 7573 (2004); g Ito et al. ACS Nano 1, 456 (2007); h Okimoto et al. J. Phys. Chem. C 112, 6103 (2008); i Tagmatarchis, et al. Chem. Mater. 12, 3222 (2000); j Kodama et al. Chem. Phys. Lett. 377, 197 (2003); k Kodama et al. J. Am. Chem. Soc. 124, 1452 (2002); l Lu et al. J. Am. Chem. Soc. 132, 5896 (2010); m Sun et al. Angew. Chem. Int. Ed. 44, 4568 (2005); n Okazaki et al. Chem. Phys. Lett. 320, 435 (2000); o Akasaka et al. J. Phys. Chem. A 112, 1294 (2008); p Olmstead, J. Am. Chem. Soc. 124, 4172 (2002); q Marcado et al. J. Am. Chem. Soc. 133, 6752 (2011); r Mercado et al. J. Am. Chem. Soc. 132, (2010); s Lu et al. Angew. Chem. Int. Ed. 51, 5889 (2012); t Nishibori et al. Chem. Phys. Lett. 298, 79 (1998); u Tsushiya et al. Angew. Chem. Int. Ed. 44, 3282 (2005); v Takata et al. Nature 377, 46 (1995); w Takano et al. J. Am. Chem. Soc. 131, 9340 (2009); x Nishibori et al. Phys. Rev. B 69, 4 (2004); y Lu et al. J. Am. Chem. Soc. 129, (2007); NATURE CHEMISTRY 11

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