Metal carbide compound containing highly charged C-2(q-) (q=5, 6) moiety is rather scarce. We show by means of density functional calculations that an unprecedented mu(4)-C-2(6-) anion can viably exist as an endohedral [Sc4C2](6+) cluster in the endofullerene Sc4C2@C-80. The electronic structure, ionization energy, electron affinity, C-13 NMR chemical shifts, vibrational frequencies, and electrochemical redox potentials of this unique endofullerene have been predicted to assist future experimental characterization.