Sm2Fe12Co3Ga2C crystallizes in the monoclinic C2/m space group. Sm(1) is bonded in a distorted single-bond geometry to four equivalent Fe(4), six equivalent Fe(2), one Ga(1), and one C(1) atom. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Co(2), one Ga(1), and one C(1) atom. In the second Fe site, Fe(2) is bonded to three equivalent Sm(1), one Fe(1), one Fe(2), one Fe(3), three equivalent Fe(4), one Co(1), one Co(2), and one Ga(1) atom to form distorted FeSm3GaFe6Co2 cuboctahedra that share  a cornercorner with one Co(1)Ga2Fe8 cuboctahedra, corners with seven equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra, corners with two equivalent C(1)Sm2Fe4 octahedra, edges with three equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra,  a faceface with one Co(1)Ga2Fe8 cuboctahedra, faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra, and  a faceface with one C(1)Sm2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-72°. In the third Fe site, Fe(3) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Co(2), two equivalent Ga(1), and one C(1) atom. In the fourth Fe site, Fe(4) is bonded in a 12-coordinate geometry to two equivalent Sm(1), one Fe(1), one Fe(3), one Fe(4), three equivalent Fe(2), one Co(1), one Co(2), and two equivalent Ga(1) atoms. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to four equivalent Fe(2), four equivalent Fe(4), and two equivalent Ga(1) atoms to form distorted CoGa2Fe8 cuboctahedra that share corners with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra and faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra. In the second Co site, Co(2) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), and two equivalent Ga(1) atoms. Ga(1) is bonded in a 14-coordinate geometry to one Sm(1), one Fe(1), two equivalent Fe(2), two equivalent Fe(3), four equivalent Fe(4), one Co(1), two equivalent Co(2), and one Ga(1) atom. C(1) is bonded to two equivalent Sm(1), two equivalent Fe(1), and two equivalent Fe(3) atoms to form CSm2Fe4 octahedra that share corners with eight equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra and faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra.
Sm2Fe12Co3Ga2C crystallizes in the monoclinic C2/m space group. Sm(1) is bonded in a distorted single-bond geometry to four equivalent Fe(4), six equivalent Fe(2), one Ga(1), and one C(1) atom. There are two shorter (2.98 Å) and two longer (3.06 Å) Sm(1)-Fe(4) bond lengths. There are a spread of Sm(1)-Fe(2) bond distances ranging from 3.04-3.26 Å. The Sm(1)-Ga(1) bond length is 3.07 Å. The Sm(1)-C(1) bond length is 2.54 Å. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Co(2), one Ga(1), and one C(1) atom. Both Fe(1)-Fe(2) bond lengths are 2.53 Å. Both Fe(1)-Fe(4) bond lengths are 2.60 Å. Both Fe(1)-Co(2) bond lengths are 2.48 Å. The Fe(1)-Ga(1) bond length is 2.62 Å. The Fe(1)-C(1) bond length is 1.93 Å. In the second Fe site, Fe(2) is bonded to three equivalent Sm(1), one Fe(1), one Fe(2), one Fe(3), three equivalent Fe(4), one Co(1), one Co(2), and one Ga(1) atom to form distorted FeSm3GaFe6Co2 cuboctahedra that share  a cornercorner with one Co(1)Ga2Fe8 cuboctahedra, corners with seven equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra, corners with two equivalent C(1)Sm2Fe4 octahedra, edges with three equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra,  a faceface with one Co(1)Ga2Fe8 cuboctahedra, faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra, and  a faceface with one C(1)Sm2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-72°. The Fe(2)-Fe(2) bond length is 2.48 Å. The Fe(2)-Fe(3) bond length is 2.54 Å. There are a spread of Fe(2)-Fe(4) bond distances ranging from 2.56-2.66 Å. The Fe(2)-Co(1) bond length is 2.46 Å. The Fe(2)-Co(2) bond length is 2.46 Å. The Fe(2)-Ga(1) bond length is 2.62 Å. In the third Fe site, Fe(3) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Co(2), two equivalent Ga(1), and one C(1) atom. Both Fe(3)-Fe(4) bond lengths are 2.48 Å. Both Fe(3)-Co(2) bond lengths are 2.46 Å. Both Fe(3)-Ga(1) bond lengths are 2.80 Å. The Fe(3)-C(1) bond length is 1.83 Å. In the fourth Fe site, Fe(4) is bonded in a 12-coordinate geometry to two equivalent Sm(1), one Fe(1), one Fe(3), one Fe(4), three equivalent Fe(2), one Co(1), one Co(2), and two equivalent Ga(1) atoms. The Fe(4)-Fe(4) bond length is 2.55 Å. The Fe(4)-Co(1) bond length is 2.47 Å. The Fe(4)-Co(2) bond length is 2.44 Å. There is one shorter (2.81 Å) and one longer (2.84 Å) Fe(4)-Ga(1) bond length. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to four equivalent Fe(2), four equivalent Fe(4), and two equivalent Ga(1) atoms to form distorted CoGa2Fe8 cuboctahedra that share corners with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra and faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra. Both Co(1)-Ga(1) bond lengths are 2.59 Å. In the second Co site, Co(2) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), and two equivalent Ga(1) atoms. Both Co(2)-Ga(1) bond lengths are 2.60 Å. Ga(1) is bonded in a 14-coordinate geometry to one Sm(1), one Fe(1), two equivalent Fe(2), two equivalent Fe(3), four equivalent Fe(4), one Co(1), two equivalent Co(2), and one Ga(1) atom. The Ga(1)-Ga(1) bond length is 2.60 Å. C(1) is bonded to two equivalent Sm(1), two equivalent Fe(1), and two equivalent Fe(3) atoms to form CSm2Fe4 octahedra that share corners with eight equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra and faces with four equivalent Fe(2)Sm3GaFe6Co2 cuboctahedra.