The spectroscopic and thermodynamic properties of the molecules M@C-28 (M = Ce, Th, Pa+, U2+, Pu4+) are calculated using density functional theory. The systems have considerable energetic stability. It is shown that the actinide cases can be classified as "32-electron" systems, using the bonding s-, p-, d-, and f-type orbitals of the central metal. The rest of the valence molecular orbitals have purely carbon character.