While endohedral fullerenes of the type Me@C82 were extensively investigated, the structures with lower carbon cage sizes are of high interest to study the role of the carbon cage on their structure and physical properties. The existence of C72 and C74 metallofullerene structures differs from the availability of empty fullerenes which were not isolated up to now. As model structures La2@C72, TmC76 and TmC78 were chosen to study the correlation between the type of the metal incorporated and the metallofullerene cage size. The structures were prepared by the Kratschmer arc burning method and isolated by a multistep HPLC separation technique. UV-Vis-NIR and infrared spectroscopy were used at room temperature. It is shown that some metals which are present in the 2+ redox state in fullerenes (Tm) form stable exohedral structures of C78.