Endohedral metallofullerene ions containing an ionic bond of Lu-Cl were observed in a mass spectrum for the first time. A theoretical calculation has been performed on the example of LuC1@C90. The two most stable isomers are LuCl@C2(99917)-C-90 and LuCl@C-2(99914)-C-90. Interestingly, both encaged Lu Cl bonds have potential curves quite different from the Morse curve and have some energy-preferential directions relative to their outside carbon cages.