The photochemical reaction Of M-2@C-80 (M=La and Ce) with 2-adamantane-2,3'-[3H]-diazirine (1) affords the corresponding adducts by carbene addition. The adducts were characterized by spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for the adduct La-2@C-80(Ad) (2, Ad = adamantylidene) reveal that the two La atoms are collinear with the Spiro carbon of the 6,6-open adduct. It is noteworthy that the La-La distance is highly elongated by the addition of carbene. Paramagnetic C-13 NMR spectral analysis of the adduct Ce-2@C-80(Ad) (3) indicates that the two Ce atoms are also collinear with the Spiro carbon at room temperature in solution. The unique metal positions were confirmed by density functional calculations.