Y 2 @C 79 N and Tb 2 @C 79 N have been prepared by conducting the Krätschmer-Huffman electric arcprocess under 20 torr of N 2 and 280 torr of He with metal oxide doped graphite rods. These new heterofullerenes were separated from the resulting mixture of empty cage fullerenes and endohedral fullerenes by chemical separation and a two stage chromatographic process. Crystallographic data for Tb 2 @C 79 N • Ni(OEP) • 2C 6 H 6 demonstrate the presence of an 80-atom cage with idealized I h symmetry and two, widely separated Tb atoms inside with a Tb---Tb separation of 3.9020(10) Å for the major terbium sites. The EPR spectrum of the odd-electron Y 2 @C 79 N indicates that the spin density largely resides on the two, equivalent yttrium ions. Computational studies on Y 2 @C 79 N suggest that the nitrogen atom resides at a 665 ring junction in the equator on the fullerene cage and that the unpaired electron is localized in a bonding orbital between the two yttrium ions of this stable radical. Thus, the Tb-Tb bond length of the single-electron bond is the longest metal-metal bond reported so far.