Isolation and Crystallographic Characterization of Sm@C 2v (3)‑C 80 Through Cocrystal Formation with Ni II (octaethylporphyrin) or Bis(ethylenedithio)tetrathiafulvalene Hua Yang, † Zhimin Wang, ‡ Hongxiao Jin, † Bo Hong, † Ziyang Liu,* ,† Christine M. Beavers, § Marilyn M. Olmstead,* ,∥ and Alan L. Balch* ,∥ † College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China ‡ College of Biology and Environmental Engineering, Zhejiang Shuren University, Hangzhou, 310015, China § Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, United States ∥ Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, United States * S Supporting Information ABSTRACT: Sm@C 2v (3)-C 80 has been separated from the carbon soot produced by electrical arc vaporization of graphite rods doped with Sm 2 O 3 and purified. Its struc- ture has been determined by single crystal X-ray diffraction using cocrystals obtained from either Ni II (octaethylporphyrin) (Ni II (OEP)) to form Sm@C 2v (3)-C 80 · Ni II (OEP)· 1.68- (toluene) · 0.32(benzene) or bis(ethylenedithio)-tetrathiafulvalene (ET) to produce Sm@C 2v (3)-C 80 ·ET·0.5(toluene). Thus, this study offers the first opportunity to com- pare a common endohedral fullerene in two different cocrystals. Both cocrystals pro- vide consistent information on the basic structure of Sm@C 2v (3)-C 80 but show that the distribution of samarium ion sites inside the carbon cage depends upon whether Ni II (OEP) or ET is present. The samarium ion is disordered in both structures, but the prominent sites lie slightly off the 2-fold symmetry axis of the cage. Computa- tional studies at the B3LYP level indicate that Sm@C 2v (3)-C 80 is more stable than any of the other six isomers of Sm@C 80 that obey the isolated pentagon rule (IPR). The surface electrostatic potential of the interacting components in the cocrystals has been examined to identify factors responsible for the ordering of the fullerene cages. The regions of the Ni II (OEP) or ET molecules that are closest to the fullerene display negative potential, while the corresponding regions of the endohedral fullerene show positive potential in a consistent fashion in both cocrystals. ■ INTRODUCTION The isolation and structural identification of Sc 3 N@I h -C 80 , the third most abundant fullerene after the empty cages C 60 and C 70 , ushered in a new era in fullerene chemistry. 1 Sc 3 N@I h -C 80 was the first endohedral fullerene to be characterized by single crystal X-ray diffraction. The high symmetry of many fullerene cages makes crystallographic studies difficult because of the presence of various sorts of orientational disorder. 2−4 Cocrystallization of fullerenes with a metalloporphyrin such as Ni II (OEP) (OEP is the dianion of octaethylporphyrin, see Scheme 1) has been shown to produce crystals with sufficient order to allow structure determination. 5 This procedure has been used in our labora- tory 6−9 and adopted by a number of other laboratories world- wide as a means to obtain structural information on empty cage fullerenes and endohedral fullerenes. 10−14 The discovery of Sc 3 N@I h -C 80 focused attention on the highly symmetric I h -C 80 cage. For example, molecules of the type M 3 N@I h -C 80 have been prepared and isolated for M = Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, and Lu. 15 Many mixed metal analogues, such as CeSc 2 N@I h -C 80 , 16 ScGd 2 N@I h -C 80 , 17 Sc 2 GdN@I h -C 80 , and TiSc 2 N@I h -C 80 18 have been prepared, isolated, and structurally characterized. The I h -C 80 cage can also enclose other clusters including Sc 4 O 2 @I h -C 80 , 19 Sc 4 O 3 @I h -C 80 , and Sc 3 C 2 @I h -C 80 . 20 Additionally, La 2 @I h -C 80 and related dimetallic endohedrals utilize this I h -C 80 cage. 21,22 However, along with I h -C 80 , there are six other C 80 isomers that satisfy the isolated pentagon rule (IPR), which requires that there are no pentagon- pentagon contacts in the fullerene and minimizes strain within Received: August 15, 2012 Published: January 23, 2013 Scheme 1. Cocrystallization Agents Article pubs.acs.org/IC © 2013 American Chemical Society 1275 dx.doi.org/10.1021/ic301794r | Inorg. Chem. 2013, 52, 1275−1284