GdC2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd is bonded in a distorted q4 geometry to ten equivalent C atoms. There are two shorter (2.49 Å) and eight longer (2.72 Å) Gd–C bond lengths. C is bonded in a 6-coordinate geometry to five equivalent Gd and one C atom. The C–C bond length is 1.30 Å.