ThCo3 crystallizes in the trigonal R-3m space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a 9-coordinate geometry to three equivalent Co(3) and nine equivalent Co(1) atoms. In the second Th site, Th(2) is bonded in a distorted hexagonal planar geometry to six equivalent Co(2) and twelve equivalent Co(1) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Th(2), three equivalent Th(1), one Co(3), two equivalent Co(2), and four equivalent Co(1) atoms to form distorted CoTh5Co7 cuboctahedra that share corners with two equivalent Co(3)Th6Co6 cuboctahedra, corners with four equivalent Co(2)Th3Co9 cuboctahedra, corners with fifteen equivalent Co(1)Th5Co7 cuboctahedra, edges with eight equivalent Co(1)Th5Co7 cuboctahedra, faces with three equivalent Co(3)Th6Co6 cuboctahedra, faces with six equivalent Co(2)Th3Co9 cuboctahedra, and faces with eleven equivalent Co(1)Th5Co7 cuboctahedra. In the second Co site, Co(2) is bonded to three equivalent Th(2), three equivalent Co(2), and six equivalent Co(1) atoms to form distorted CoTh3Co9 cuboctahedra that share corners with three equivalent Co(2)Th3Co9 cuboctahedra, corners with three equivalent Co(3)Th6Co6 cuboctahedra, corners with twelve equivalent Co(1)Th5Co7 cuboctahedra, edges with six equivalent Co(2)Th3Co9 cuboctahedra,  a faceface with one Co(3)Th6Co6 cuboctahedra, faces with three equivalent Co(2)Th3Co9 cuboctahedra, and faces with eighteen equivalent Co(1)Th5Co7 cuboctahedra. In the third Co site, Co(3) is bonded to six equivalent Th(1) and six equivalent Co(1) atoms to form CoTh6Co6 cuboctahedra that share corners with six equivalent Co(2)Th3Co9 cuboctahedra, corners with twelve equivalent Co(1)Th5Co7 cuboctahedra, edges with six equivalent Co(3)Th6Co6 cuboctahedra, faces with two equivalent Co(2)Th3Co9 cuboctahedra, and faces with eighteen equivalent Co(1)Th5Co7 cuboctahedra.
ThCo3 crystallizes in the trigonal R-3m space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a 9-coordinate geometry to three equivalent Co(3) and nine equivalent Co(1) atoms. All Th(1)-Co(3) bond lengths are 2.97 Å. There are six shorter (2.87 Å) and three longer (3.30 Å) Th(1)-Co(1) bond lengths. In the second Th site, Th(2) is bonded in a distorted hexagonal planar geometry to six equivalent Co(2) and twelve equivalent Co(1) atoms. All Th(2)-Co(2) bond lengths are 2.87 Å. All Th(2)-Co(1) bond lengths are 3.21 Å. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Th(2), three equivalent Th(1), one Co(3), two equivalent Co(2), and four equivalent Co(1) atoms to form distorted CoTh5Co7 cuboctahedra that share corners with two equivalent Co(3)Th6Co6 cuboctahedra, corners with four equivalent Co(2)Th3Co9 cuboctahedra, corners with fifteen equivalent Co(1)Th5Co7 cuboctahedra, edges with eight equivalent Co(1)Th5Co7 cuboctahedra, faces with three equivalent Co(3)Th6Co6 cuboctahedra, faces with six equivalent Co(2)Th3Co9 cuboctahedra, and faces with eleven equivalent Co(1)Th5Co7 cuboctahedra. The Co(1)-Co(3) bond length is 2.63 Å. There is one shorter (2.48 Å) and one longer (2.50 Å) Co(1)-Co(2) bond length. There are two shorter (2.47 Å) and two longer (2.50 Å) Co(1)-Co(1) bond lengths. In the second Co site, Co(2) is bonded to three equivalent Th(2), three equivalent Co(2), and six equivalent Co(1) atoms to form distorted CoTh3Co9 cuboctahedra that share corners with three equivalent Co(2)Th3Co9 cuboctahedra, corners with three equivalent Co(3)Th6Co6 cuboctahedra, corners with twelve equivalent Co(1)Th5Co7 cuboctahedra, edges with six equivalent Co(2)Th3Co9 cuboctahedra,  a faceface with one Co(3)Th6Co6 cuboctahedra, faces with three equivalent Co(2)Th3Co9 cuboctahedra, and faces with eighteen equivalent Co(1)Th5Co7 cuboctahedra. All Co(2)-Co(2) bond lengths are 2.87 Å. In the third Co site, Co(3) is bonded to six equivalent Th(1) and six equivalent Co(1) atoms to form CoTh6Co6 cuboctahedra that share corners with six equivalent Co(2)Th3Co9 cuboctahedra, corners with twelve equivalent Co(1)Th5Co7 cuboctahedra, edges with six equivalent Co(3)Th6Co6 cuboctahedra, faces with two equivalent Co(2)Th3Co9 cuboctahedra, and faces with eighteen equivalent Co(1)Th5Co7 cuboctahedra.