Tb 2 O@ C 2 (13333)-C 74 : A Non-Isolated Pentagon Endohedral Fullerene Containing a Nearly Linear Tb-O-Tb Unit.

Terbium has been added to the list of elements that form oxide clusters inside fullerene cages. Tb 2 O@ C 2 (13333)-C 74 has been isolated as a byproduct of the electric arc synthesis of the azafullerene Tb 2 @C 79 N. Cocrystallization of Tb 2 O@ C 2 (13333)-C 74 with Ni(OEP) (where OEP is the dianion of octaethylporphyrin) in toluene yielded black needles of Tb 2 O@ C 2 (13333)-C 74 ·Ni II (OEP)·1.5C 7 H 8 that have been examined by single-crystal X-ray diffraction. The resulting structure shows that a nearly linear Tb-O-Tb unit is contained in a C 2 (13333)-C 74 , which has two sites where pentagons share an edge to form pentalene units at opposite ends of the fullerene. Unlike the usual situations where metal atoms in fullerenes that do not obey the isolated pentagon rule are situated within the folds of the pentalene units, the Tb atoms in Tb 2 O@ C 2 (13333)-C 74 are positioned to the side of the pentalene units and near-neighboring hexagons. The magnetic properties of Tb 2 O@ C 2 (13333)-C 74 have been examined starting from the experimental geometry, using ab-initio multiconfigurational methods. The computations predict that Tb 2 O@ C 2 (13333)-C 74 will show strong axiality, which would make it a single-molecule magnet with a large magnetic anisotropy barrier.