Sc5Ir15C4 crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to four equivalent Ir(1), four equivalent Ir(4), and four equivalent Ir(5) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(2)Ir12 cuboctahedra, corners with eight equivalent Sc(1)Ir12 cuboctahedra,  a faceface with one Sc(2)Ir12 cuboctahedra, faces with five equivalent Sc(1)Ir12 cuboctahedra, and faces with four equivalent C(1)Ir6 octahedra. In the second Sc site, Sc(2) is bonded to four equivalent Ir(2), four equivalent Ir(5), and four equivalent Ir(6) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(1)Ir12 cuboctahedra, corners with four equivalent Sc(2)Ir12 cuboctahedra, corners with four equivalent Sc(3)Ir12 cuboctahedra,  a faceface with one Sc(1)Ir12 cuboctahedra,  a faceface with one Sc(3)Ir12 cuboctahedra, faces with four equivalent Sc(2)Ir12 cuboctahedra, faces with four equivalent C(1)Ir6 octahedra, and faces with four equivalent C(2)Ir6 octahedra. In the third Sc site, Sc(3) is bonded to four equivalent Ir(3) and eight equivalent Ir(6) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(3)Ir12 cuboctahedra, corners with eight equivalent Sc(2)Ir12 cuboctahedra, faces with two equivalent Sc(2)Ir12 cuboctahedra, faces with four equivalent Sc(3)Ir12 cuboctahedra, and faces with eight equivalent C(2)Ir6 octahedra. There are six inequivalent Ir sites. In the first Ir site, Ir(1) is bonded in a distorted single-bond geometry to four equivalent Sc(1) and one C(1) atom. In the second Ir site, Ir(2) is bonded in a 6-coordinate geometry to four equivalent Sc(2), one C(1), and one C(2) atom. In the third Ir site, Ir(3) is bonded to four equivalent Sc(3) and two equivalent C(2) atoms to form a mixture of distorted edge and corner-sharing IrSc4C2 octahedra. The corner-sharing octahedra are not tilted. In the fourth Ir site, Ir(4) is bonded in a distorted square co-planar geometry to four equivalent Sc(1) atoms. In the fifth Ir site, Ir(5) is bonded in a 2-coordinate geometry to two equivalent Sc(1), two equivalent Sc(2), and two equivalent C(1) atoms. In the sixth Ir site, Ir(6) is bonded in a distorted linear geometry to two equivalent Sc(2), two equivalent Sc(3), and two equivalent C(2) atoms. There are two inequivalent C sites. In the first C site, C(1) is bonded to one Ir(1), one Ir(2), and four equivalent Ir(5) atoms to form distorted CIr6 octahedra that share  a cornercorner with one C(2)Ir6 octahedra, corners with four equivalent C(1)Ir6 octahedra, faces with four equivalent Sc(1)Ir12 cuboctahedra, and faces with four equivalent Sc(2)Ir12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-22°. In the second C site, C(2) is bonded to one Ir(2), one Ir(3), and four equivalent Ir(6) atoms to form CIr6 octahedra that share  a cornercorner with one C(1)Ir6 octahedra, corners with five equivalent C(2)Ir6 octahedra, faces with four equivalent Sc(2)Ir12 cuboctahedra, and faces with four equivalent Sc(3)Ir12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-7°.
Sc5Ir15C4 crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to four equivalent Ir(1), four equivalent Ir(4), and four equivalent Ir(5) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(2)Ir12 cuboctahedra, corners with eight equivalent Sc(1)Ir12 cuboctahedra,  a faceface with one Sc(2)Ir12 cuboctahedra, faces with five equivalent Sc(1)Ir12 cuboctahedra, and faces with four equivalent C(1)Ir6 octahedra. All Sc(1)-Ir(1) bond lengths are 2.89 Å. All Sc(1)-Ir(4) bond lengths are 2.79 Å. All Sc(1)-Ir(5) bond lengths are 3.06 Å. In the second Sc site, Sc(2) is bonded to four equivalent Ir(2), four equivalent Ir(5), and four equivalent Ir(6) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(1)Ir12 cuboctahedra, corners with four equivalent Sc(2)Ir12 cuboctahedra, corners with four equivalent Sc(3)Ir12 cuboctahedra,  a faceface with one Sc(1)Ir12 cuboctahedra,  a faceface with one Sc(3)Ir12 cuboctahedra, faces with four equivalent Sc(2)Ir12 cuboctahedra, faces with four equivalent C(1)Ir6 octahedra, and faces with four equivalent C(2)Ir6 octahedra. All Sc(2)-Ir(2) bond lengths are 2.89 Å. All Sc(2)-Ir(5) bond lengths are 2.85 Å. All Sc(2)-Ir(6) bond lengths are 2.95 Å. In the third Sc site, Sc(3) is bonded to four equivalent Ir(3) and eight equivalent Ir(6) atoms to form ScIr12 cuboctahedra that share corners with four equivalent Sc(3)Ir12 cuboctahedra, corners with eight equivalent Sc(2)Ir12 cuboctahedra, faces with two equivalent Sc(2)Ir12 cuboctahedra, faces with four equivalent Sc(3)Ir12 cuboctahedra, and faces with eight equivalent C(2)Ir6 octahedra. All Sc(3)-Ir(3) bond lengths are 2.89 Å. All Sc(3)-Ir(6) bond lengths are 2.88 Å. There are six inequivalent Ir sites. In the first Ir site, Ir(1) is bonded in a distorted single-bond geometry to four equivalent Sc(1) and one C(1) atom. The Ir(1)-C(1) bond length is 1.94 Å. In the second Ir site, Ir(2) is bonded in a 6-coordinate geometry to four equivalent Sc(2), one C(1), and one C(2) atom. The Ir(2)-C(1) bond length is 2.39 Å. The Ir(2)-C(2) bond length is 2.01 Å. In the third Ir site, Ir(3) is bonded to four equivalent Sc(3) and two equivalent C(2) atoms to form a mixture of distorted edge and corner-sharing IrSc4C2 octahedra. The corner-sharing octahedra are not tilted. Both Ir(3)-C(2) bond lengths are 2.15 Å. In the fourth Ir site, Ir(4) is bonded in a distorted square co-planar geometry to four equivalent Sc(1) atoms. In the fifth Ir site, Ir(5) is bonded in a 2-coordinate geometry to two equivalent Sc(1), two equivalent Sc(2), and two equivalent C(1) atoms. Both Ir(5)-C(1) bond lengths are 2.08 Å. In the sixth Ir site, Ir(6) is bonded in a distorted linear geometry to two equivalent Sc(2), two equivalent Sc(3), and two equivalent C(2) atoms. Both Ir(6)-C(2) bond lengths are 2.05 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded to one Ir(1), one Ir(2), and four equivalent Ir(5) atoms to form distorted CIr6 octahedra that share  a cornercorner with one C(2)Ir6 octahedra, corners with four equivalent C(1)Ir6 octahedra, faces with four equivalent Sc(1)Ir12 cuboctahedra, and faces with four equivalent Sc(2)Ir12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-22°. In the second C site, C(2) is bonded to one Ir(2), one Ir(3), and four equivalent Ir(6) atoms to form CIr6 octahedra that share  a cornercorner with one C(1)Ir6 octahedra, corners with five equivalent C(2)Ir6 octahedra, faces with four equivalent Sc(2)Ir12 cuboctahedra, and faces with four equivalent Sc(3)Ir12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-7°.