The reaction of tetrazine 1 with Sc3C2@C-80 exclusively affords the open-cage derivative 2 instead of the expected C-2-inserted derivative 3 bearing a four-membered ring, as previously obtained for C-60. The structure of 2 has been firmly established by NMR spectroscopy and theoretical calculations. EPR spectroscopy shows that a single Sc atom of the Sc3C2 cluster gets located within the bulge created by the bridging addend, which is a first step toward release of the internal metal atoms.