Petra Georgi

New metallofullerenes in the size gap of C70 to C82: From La2@C72 to Sc3N@C80

The yield and stability of fullerenes with carbon cages in the size gap between C 70 and C 84 is strongly dependent on the metals included. It is shown for C 72 and C 74 cages that they can be stabilised by metal ion inclusion. A review is given for new fullerene structures. A number of new endohedral fullerenes were isolated and described in their optical and redox properties. New fullerene structures presented are: La 2 @C 72 , Ce 2 @C 72 , Eu@C 74 , Tm@C 78 , and Sc 3 N@C 80 . The existence of a selected cage size and isomeric cage is discussed with respect to the metal and its redox state.

Sc2@C76(C2): a new isomerism in fullerene structure

Abstract Sc 2 @C 76 was for the first time isolated and characterized spectroscopically. It is suggested from the 13 C NMR spectroscopy ( 13 C NMR pattern: 38×2) that this metallofullerene has a C 2 symmetry, in contrast to the D 2 symmetry of an empty C 76 fullerene cage. Ab initio calculations were performed to explore the symmetry changes for C 76 (from D 2 to C 2 ) induced by the endohedral scandium ions. It is found that the scandium ions are located at two of the three main C 2 axes of C 76 ( D 2 ). The two isomers Sc 2 @C 76 ( D 2− x ) (Sc 2 was put along the C 2 x axis of C 76 ( D 2 )) and Sc 2 @C 76 ( D 2− y ) (Sc 2 was put along the C 2 y axis of C 76 ( D 2 )) are nearly iso-energetic in their optimised geometrical structures, and their energies are much lower than that of the third isomer Sc 2 @C 76 ( D 2− z ) (Sc 2 was put along the C 2 z axis of C 76 ( D 2 )). Each of the two iso-energetic isomers, i.e., Sc 2 @C 76 ( D 2− x ) and Sc 2 @C 76 ( D 2− y ), contributes 19 NMR lines ( 13 C NMR pattern: 19×4), so the mixture of them shows overall 38 NMR lines ( 13 C NMR pattern: 38×2) for this metallofullerene.

Isolation and FTIR analysis of endohedral L3−xMxN@C80 (0 ⩽ × ⩽ 3) fullerenes

L3−xMxN@C80 (0 ⩽ × ⩽ 3; M = Sc, Y, Tb, Ho, Er) fullerenes have been isolated and studied by FTIR spectroscopy. Ionic radii and cage size are shown to affect the structure of the encaged trimetal nitride cluster. A correlation between cluster size, metal‐nitrogen bond strength and stability of M3N@C80 fullerenes is proposed.

The samarium fullerene family

Among the rare earth metals samarium is expected to form an ion of the two-valent redox state in endohedral fullerene structures. As compared to thulium and europium metallofullerenes a similar distribution of carbon cage structures is expected for samarium. The samarium fullerene structures produced by the Kratschmer-Huffman method were studied with respect to the influence of the Sm-carbon ratio on the type and yield of the metallofullerenes. The chromatographic separation carried out by a two step HPLC resulted in a larger family of Sm-fullerenes (C2n, 2n=74, 78, 82, 84, 86, 88, 90, 92) encapsulating one ion as detected by mass spectrometry. Only the Sm-C76 structure was missing. No dimetallofullerenes of Sm were found. The samarium structures of C74 and C82 were characterized by UV-Vis and IR spectroscopy. The results were compared with those of Eu@C74 and Tm@C82. The redox state of the metal ion in the metallofullerene was shown to be Sm2+

Endohedral fullerenes with lower carbon cage sizes

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.