Isolation and Crystallographic Characterization of ErSc₂N@C₈₀: an Endohedral Fullerene Which Crystallizes with Remarkable Internal Order

Abstract

The ErnSc3-nN@C80 (n = 0−3) family of four endohedral fullerenes has been prepared by vaporization of graphite rods packed with 2% Sc2O3/3% Er2O3/95% graphite powder in a Krätschmer−Huffman fullerene generator under dynamic flow of helium and dinitrogen. ErSc2N@C80 has been isolated in pure form via three stages of high-pressure liquid chromatography and characterized by mass spectrometry. The first structure of a mixed metal endohedral, ErSc2N@C80, has been determined by single-crystal X-ray diffraction at 90 K on ErSc2N@C80·CoII(OEP)·1.5C6H6·0.3CHCl3, which was obtained by diffusion of a solution of ErSc2N@C80 in benzene into a solution of CoII(OEP) (OEP is the dianion of octaethylporphyrin) in chloroform. The structure of ErSc2N@C80 consists of a planar ErSc2N unit surrounded by an icosahedral C80 cage. The nominal Er−N distance is 2.089(9) Å and the Sc−N distance is, as expected, shorter, 1.968(6) Å. Despite its location within the C80 cage, the ErSc2N unit displays a remarkable degree of order within the solid-state structure. The metal ions make close contact with individual carbon atoms of the cage with shortest Sc−C distances, in the range of 2.03−2.12 Å, and shortest Er−C distances of 2.20 and 2.22 Å. Two different, but equally populated, orientations of the Ih C80 cage were required to describe the fullerene portion of the structure. Although these C80 cages are located on a crystallographic mirror plane, that plane does not coincide with a mirror plane of the cages themselves. Consequently, the cage is disordered over four superimposed sites.