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Fe4C crystallizes in the tetragonal I4/m space group. The structure is one-dimensional and consists of two Fe4C ribbons oriented in the (0, 0, 1) direction. Fe is bonded in a 2-coordinate geometry to two equivalent C atoms. Both Fe–C bond lengths are 2.07 Å. C is bonded in a body-centered cubic geometry to eight equivalent Fe atoms.
Fe4C is Iron carbide structured and crystallizes in the cubic P-43m space group. The structure is zero-dimensional and consists of one carbanide;iron molecule. Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.79 Å. C is bonded in a tetrahedral geometry to four equivalent Fe atoms.
Fe4C crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in an L-shaped geometry to two equivalent Fe and two equivalent C atoms. Both Fe–Fe bond lengths are 2.61 Å. Both Fe–C bond lengths are 2.01 Å. In the second Fe site, Fe is bonded in a 3-coordinate geometry to three equivalent Fe and three equivalent C atoms. There are one shorter (2.50 Å) and two longer (2.51 Å) Fe–Fe bond lengths. There are two shorter (1.98 Å) and one longer (2.29 Å) Fe–C bond lengths. In the third Fe site, Fe is bonded in an L-shaped geometry to three equivalent Fe and two equivalent C atoms. There are one shorter (2.43 Å) and two longer (2.58 Å) Fe–Fe bond lengths. Both Fe–C bond lengths are 1.98 Å. In the fourth Fe site, Fe is bonded in a 1-coordinate geometry to twelve Fe and one C atom. There are two shorter (2.64 Å) and two longer (2.65 Å) Fe–Fe bond lengths. The Fe–C bond length is 2.52 Å. C is bonded in a 6-coordinate geometry to eight Fe atoms.