The Er(n)S3(c-n)N@C-80 (n = 0-3) family of four endohedral fullerenes has been prepared by vaporization of graphite rods packed with 2% Sc2O3/% Er2O3/95% graphite powder in a Kratschmer-Huffman fullerene generator under dynamic flow of helium and dinitrogen. ErSc2N@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, ErSc2N@C-80, has been determined by single-crystal IL-ray diffraction at 90 K on ErSc2N@C-80. Co-II(OEP).1.5C(6)H(6).0.3CHCl(3), which was obtained by diffusion of a solution of ErSc2N@C-80 in benzene into a solution of Co-II(OEP) (OEP is the dianion of octaethylporphyrin) in chloroform, The structure of ErSc2N@C-80 consists of a planar ErSc2N unit surrounded by an icosahedral C-80 cage. The nominal Er-N distance is 2.089(9) Angstrom and the Sc-N distance is, as expected, shorter, 1.968(6) Angstrom. Despite its location within the C-80 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 Angstrom, arid;;shortest Er-C distances of 2.20 and 2.22 Angstrom. Two different, but equally populated, orientations of the Ih Csd 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.