The molecular structures of Tm-2@C-82(C-s(6)) and Tm2C2@C-82(C-s(6)) are determined by means of single crystal X-ray diffraction using the co-crystals with nickel octaethylporphyrin (Ni(OEP)). The molecular orientations and Tm positions of Tm-2@C-82(C-s(6)) and Tm2C2@C-82(C-s(6)) are basically the same each other. One of the two Tm positions is very close to the Tm position of Tm@C-82(C-s(6)). These facts demonstrate that the stable endohedral Tm positions are not fundamentally affected by the addition of the other Tm atoms but dependent on the kind of the fullerene cage structure. (C) 2014 Elsevier B.V. All rights reserved.