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

Abstract

The Er n Sc 3 - n N@C 80 ( n = 0−3) family of four endohedral fullerenes has been prepared by vaporization of graphite rods packed with 2% Sc 2 O 3 /3% Er 2 O 3 /95% graphite powder in a Krätschmer−Huffman fullerene generator under dynamic flow of helium and dinitrogen. ErSc 2 N@C 80 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, ErSc 2 N@C 80, has been determined by single-crystal X-ray diffraction at 90 K on ErSc 2 N@C 80 ·Co II (OEP)·1.5C 6 H 6 ·0.3CHCl 3, which was obtained by diffusion of a solution of ErSc 2 N@C 80 in benzene into a solution of Co II (OEP) (OEP is the dianion of octaethylporphyrin) in chloroform. The structure of ErSc 2 N@C 80 consists of a planar ErSc 2 N unit surrounded by an icosahedral C 80 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 C 80 cage, the ErSc 2 N 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 I h C 80 cage were required to describe the fullerene portion of the structure. Although these C 80 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.