Separation difficulties have led to a paucity of purified metallic nitride fullerenes (MNFs). Fundamental research and application development has been hampered with limited sample availability. Separation techniques designed to remove contaminant empty-cage fullerenes (e.g., C(60), C(70)...C(2)(n)) and classical metallofullerenes (e.g., non-MNFs) traditionally require expensive and tedious chromatographic methods. Our motivation is an alternative purification approach to minimize dependence on HPLC. Herein we report the use of cyclopentadienyl (CPD) and amino functionalized silica to selectively bind contaminant fullerenes. This "Stir and Filter Approach" (SAFA) provides purified MNF samples at ambient and reflux conditions. Under reflux conditions, purified MNFs (80% recovery, 41 h) are obtained using CPD silica. However, at room temperature, there is an equilibrium established between fullerenes and CPD silica, and no purified MNF samples are obtained using SAFA. In contrast, purified MNF samples (99+%) are readily obtained at room temperature using amino, diamino, and triamino silica at recoveries of 93% (11 h), 76% (9 h), and 50% (6 h), respectively.

The tetrahedral array of four scandium atoms with oxygen atoms capping three of the four faces found in Sc(4)(mu(3)-O)(3)@I(h)-C(80) is the largest cluster isolated to date inside a fullerene cage.

Endohedral metallic nitride fullerenes (MNFs; a subset of endohedral metallofullerenes, EMFs) have attracted increasing attention since their discovery, 1 not only because they possess unique structures but also because exohedral derivatives of them may find use in important medical applications such as MRI or X-ray contrast agents. 2 Recently, some of us developed an efficient, nonchromatographic purification that makes these compounds available in larger quantities than any EMF reported to date. 3 Exohedral modifications of MNFs have been largely limited to cycloadditions. 4 Taken together, refs 3, 4 and references therein have repeatedly shown that the Sc 3 N@(C 80 -I h ) isomer is much less reactive than the D 5h cage isomer.We now report the preparation, isolation, and spectroscopic and electrochemical characterization of the first CF 3 derivatives of both isomers of Sc 3 N@C 80 . 5 Hollow fullerene(CF 3 ) n derivatives are sufficiently volatile to sublime out of the hot zone during reaction with flowing CF 3 I; 6 EMF(CF 3 ) n compounds are not, 7 and the compounds described here were extracted from the crude product mixture with organic solvents. The first washings (hexane and toluene) contained Sc 3 N@C 80 (CF 3 ) n (8 e n e 12; these will be described in the full paper). The o-dichlorobenzene washings contained predominantly two compositions, Sc 3 N@C 80 and Sc 3 N@C 80 (CF 3 ) 2 , (5:1 HPLC peak areas ratio), with small amounts of Sc 3 N@C 80 (CF 3 ) 4,6 . Mass and 19 F NMR spectra of HPLC-purified Sc 3 N@C 80 (CF 3 ) 2 8 are shown in Figure 1. The bis-CF 3 derivative prepared with purified Sc 3 N@C 80 -I h exhibited an 19 F singlet at δ -71.4, indicating either symmetry-related CF 3 groups or CF 3 groups rendered chemical-shift equivalent by rapid reorientation of the Sc 3 N cluster inside the cage. The derivative prepared with the 9:1 mixture of cage isomers exhibited two singlets, at δ -71.4 (rel. int. 7) and -73.3 (rel. int. 1). It is virtually certain that the compound with δ -73.3 belongs to Sc 3 N@(C 80 -D 5h ). Therefore, notwithstanding the previously reported differences in reactivity of Sc 3 N@(C 80 -I h ) and Sc 3 N@(C 80 -D 5h ), we conclude that these two compounds react with CF 3 radicals at essentially the same rate at 520 ( 10°C.If we avoid triple-hexagon junctions and assume para addition of two CF 3 groups to a C 80 -I h hexagon, which is the most likely addition pattern, 9 there are still many possible orientations of the Sc 3 N cluster. DFT calculations (see ref 6 for details) were performed for more than 20 isomers of Sc 3 N@(C 80 -I h )(CF 3 ) 2 in which different cluster positions were chosen as starting points for geometry optimization. The two most stable optimized structures each have two of the three Sc atoms bonded to the cage C atom that is para to each of the cage C(CF 3 ) atoms, as shown in Figure 2. This results in a para 3 ribbon of edge sharing hexagons with the sequence C(Sc)‚‚‚C(CF 3 )‚‚‚C(CF 3 )‚‚‚C(Sc). Para only sequences of C 6 (CF 3 ) 2 hexagons have been reporte...