State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 Title: Capturing the Labile Fullerene[50] as C50Cl10 Authors References and Notes Figure and Figure Caption

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 Figure 1 A) Exptl. & Theor. NMR of C 50 Cl 10. B) Structure of C 50 Cl 10

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 All carbon cages (fullerenes) synthesized so far, such as C 60 and its larger homologs, faithfully satisfy geometric “isolated pentagon rule” (IPR) (1), that governs the stability of fullerenes comprising hexagons and exactly twelve pentagons (1). The smaller non-IPR fullerenes (2-9), which are predicted to have unusual properties because of their adjacent pentagons and high curvature (2-8), are so labile that their properties and reactivity have only be studied in the gas phase (1-3).

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 Experimental efforts directed at their bulk synthesis have produced some results(4-6), but complete structural characterization is still under way(7). Here we report the synthesis in milligram quantity of a small non-IPR fullerene C 50, a long-sought smaller sister of C 60 (1, 3, 7, 8), through the introduction of chlorine in the form of carbon tetrachloride (CCl 4 ) during synthesis from graphite.

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 C 50 -containing soot (ca. 90 g) was synthesized in a modified graphite arc- discharge process (9) with 10 Torr carbon tetrachloride being added to 300 Torr helium atmosphere. The toluene-extract from the soot was isolated by a multistage high-performance liquid chromatography (10), and ca. 2 mg C 50 Cl 10 with 99.5% purity was obtained. The C 50 Cl 10 thus-obtained is moderately soluble in some organic solvents, e.g. carbon disulfide, toluene and benzene, as lemon-yellow colored solutions.

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 Fig. 1A shows the experimental 13 C NMR spectrum for the C 50 Cl 10 measured in deuterated benzene. Four distinct signals are located at 161.5, 146.6, and 88.7 ppm, respectively, with the intensity ratio of approximately 2:1:1:1; the former three signals are characteristic of sp 2 -hybridised carbons, whereas the latter one is typical of sp 3 - hybridised carbons connected to chlorine. This indicates four unique types of carbon atoms in the C 50 Cl 10 with the C(sp 2 ):C(sp 3 ) ratio of 4:1. Among numerous possible structures in the C 50 isomers family (3, 8), only the D 5h fullerene[50] has four unique types of carbon atoms (I-IV, as illustrated in Fig. 1B).

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 The ten chlorine atoms should be added to the most reactive C IV sites (i.e., pentagon-pentagon fusions), giving rise to a decachlorofullerene[50] molecule (Fig. 1B). Indeed, the theoretically simulated 13 C NMR spectrum (the inset to Fig. 1A) of this Saturn-shaped C 50 Cl 10 structure agrees well with the experimental one. Additionally, the D 5h fullerene[50] structure has been further co-characterized by a variety of technologies including mass spectrum, infrared absorption, Raman, UV-Vis absorption and fluorescence spectroscopies (10).

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 Fullerenes smaller than C 60 were predicted to have unusual electronic, magnetic and mechanical properties arising mainly from the significant curvature of their molecular surface (1-7). Hindered by the synthetic difficulty, however, experimental investigation on these properties is scarce. Our successful capture of C 50 not only brings into reality a long-sought member of the fullerene family, but also reveals that small non- IPR fullerenes can be obtained in macroscopic quantities by saturating the highly active sites of the otherwise extremely unstable cage. We have chromatographic evidence that other small fullerenes such as C 56 and C 54 are trapped in the CCl 4 arc-discharge process (10).

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 The chlorinated small fullerenes thus obtained have their curved cage surfaces maintained and, in the meantime, are ready for further chemical manipulations. For example, Cl groups of C 50 Cl 10 can be replaced by reaction with methanol under mild conditions. This result implies that some of the curvature-related unusual properties of small fullerenes are retained in their chlorinated forms, and, more significantly, opens a door for routine experimental investigations of the properties and applications of small fullerenes and their derivatives.

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 References and Notes 1. K. M. Kadish, R. S. Ruoff, (ed.) Fullerene: Chemistry, Physics and Technology, (A John Wiley & Sons, New York, 2002). 2. T. Guo et al., Science 257, 1661 (1992). 3. H. W. Kroto, Nature 329, 529 (1987). 4. C. Piskoti, J. Yarger, A. Zettl, Nature 393, 771 (1998). 5. A. Koshio, M. Inakuma, T. Sugai, H. Shinohara, J. Am. Chem. Soc. 122, 398 (2000). 6. P. W. Fowler,T. Heine, J. Chem. Soc., Perkin Trans (2001).

State Key Laboratory for Physical Chemistry of Solid Surfaces 厦门大学固体表面物理化学国家重点实验室 7. J. R. Heath, Nature 393, 730 (1998). 8. D. Bakowies, W. Thiel, J. Am. Chem. Soc. 113, 3704 (1991). 9. F. Gao, S. Y. Xie, R. B. Huang,L. S. Zheng, Chem. Commun (2003). 10. Supporting information is available online. 11. We thank Prof. R. E. Smalley and for critical reviewing the manuscript and providing suggestions. Supported by NSFC, MST and MOE of China.