Ni9Al3C crystallizes in the tetragonal P4/mmm space group. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a single-bond geometry to four equivalent Ni(4), four equivalent Al(1), and one C(1) atom. In the second Ni site, Ni(2) is bonded to eight equivalent Ni(4) and four equivalent Al(2) atoms to form NiAl4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with eight equivalent Al(1)Ni12 cuboctahedra, edges with sixteen equivalent Ni(4)Al4Ni8 cuboctahedra, faces with four equivalent Ni(2)Al4Ni8 cuboctahedra, faces with four equivalent Al(2)Ni12 cuboctahedra, and faces with eight equivalent Ni(4)Al4Ni8 cuboctahedra. In the third Ni site, Ni(3) is bonded in a linear geometry to four equivalent Al(1) and two equivalent C(1) atoms. In the fourth Ni site, Ni(4) is bonded to two equivalent Ni(1), two equivalent Ni(2), four equivalent Ni(4), two equivalent Al(1), and two equivalent Al(2) atoms to form distorted NiAl4Ni8 cuboctahedra that share corners with eight equivalent Ni(4)Al4Ni8 cuboctahedra, corners with two equivalent C(1)Ni6 octahedra, edges with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with four equivalent Ni(4)Al4Ni8 cuboctahedra, edges with four equivalent Al(1)Ni12 cuboctahedra, edges with four equivalent Al(2)Ni12 cuboctahedra, faces with two equivalent Ni(2)Al4Ni8 cuboctahedra, faces with two equivalent Al(1)Ni12 cuboctahedra, faces with two equivalent Al(2)Ni12 cuboctahedra, and faces with nine equivalent Ni(4)Al4Ni8 cuboctahedra. The corner-sharing octahedral tilt angles are 47°. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to four equivalent Ni(1), four equivalent Ni(3), and four equivalent Ni(4) atoms to form AlNi12 cuboctahedra that share corners with four equivalent Al(2)Ni12 cuboctahedra, corners with eight equivalent Al(1)Ni12 cuboctahedra, edges with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with eight equivalent Ni(4)Al4Ni8 cuboctahedra,  a faceface with one Al(2)Ni12 cuboctahedra, faces with four equivalent Ni(4)Al4Ni8 cuboctahedra, faces with five equivalent Al(1)Ni12 cuboctahedra, and faces with four equivalent C(1)Ni6 octahedra. In the second Al site, Al(2) is bonded to four equivalent Ni(2) and eight equivalent Ni(4) atoms to form AlNi12 cuboctahedra that share corners with four equivalent Al(2)Ni12 cuboctahedra, corners with eight equivalent Al(1)Ni12 cuboctahedra, edges with sixteen equivalent Ni(4)Al4Ni8 cuboctahedra, faces with two equivalent Al(1)Ni12 cuboctahedra, faces with four equivalent Ni(2)Al4Ni8 cuboctahedra, faces with four equivalent Al(2)Ni12 cuboctahedra, and faces with eight equivalent Ni(4)Al4Ni8 cuboctahedra. C(1) is bonded to two equivalent Ni(1) and four equivalent Ni(3) atoms to form CNi6 octahedra that share corners with eight equivalent Ni(4)Al4Ni8 cuboctahedra, corners with four equivalent C(1)Ni6 octahedra, and faces with eight equivalent Al(1)Ni12 cuboctahedra. The corner-sharing octahedra are not tilted.
Ni9Al3C crystallizes in the tetragonal P4/mmm space group. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a single-bond geometry to four equivalent Ni(4), four equivalent Al(1), and one C(1) atom. All Ni(1)-Ni(4) bond lengths are 2.53 Å. All Ni(1)-Al(1) bond lengths are 2.61 Å. The Ni(1)-C(1) bond length is 1.86 Å. In the second Ni site, Ni(2) is bonded to eight equivalent Ni(4) and four equivalent Al(2) atoms to form NiAl4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with eight equivalent Al(1)Ni12 cuboctahedra, edges with sixteen equivalent Ni(4)Al4Ni8 cuboctahedra, faces with four equivalent Ni(2)Al4Ni8 cuboctahedra, faces with four equivalent Al(2)Ni12 cuboctahedra, and faces with eight equivalent Ni(4)Al4Ni8 cuboctahedra. All Ni(2)-Ni(4) bond lengths are 2.50 Å. All Ni(2)-Al(2) bond lengths are 2.61 Å. In the third Ni site, Ni(3) is bonded in a linear geometry to four equivalent Al(1) and two equivalent C(1) atoms. All Ni(3)-Al(1) bond lengths are 2.69 Å. Both Ni(3)-C(1) bond lengths are 1.85 Å. In the fourth Ni site, Ni(4) is bonded to two equivalent Ni(1), two equivalent Ni(2), four equivalent Ni(4), two equivalent Al(1), and two equivalent Al(2) atoms to form distorted NiAl4Ni8 cuboctahedra that share corners with eight equivalent Ni(4)Al4Ni8 cuboctahedra, corners with two equivalent C(1)Ni6 octahedra, edges with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with four equivalent Ni(4)Al4Ni8 cuboctahedra, edges with four equivalent Al(1)Ni12 cuboctahedra, edges with four equivalent Al(2)Ni12 cuboctahedra, faces with two equivalent Ni(2)Al4Ni8 cuboctahedra, faces with two equivalent Al(1)Ni12 cuboctahedra, faces with two equivalent Al(2)Ni12 cuboctahedra, and faces with nine equivalent Ni(4)Al4Ni8 cuboctahedra. The corner-sharing octahedral tilt angles are 47°. All Ni(4)-Ni(4) bond lengths are 2.61 Å. Both Ni(4)-Al(1) bond lengths are 2.46 Å. Both Ni(4)-Al(2) bond lengths are 2.50 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to four equivalent Ni(1), four equivalent Ni(3), and four equivalent Ni(4) atoms to form AlNi12 cuboctahedra that share corners with four equivalent Al(2)Ni12 cuboctahedra, corners with eight equivalent Al(1)Ni12 cuboctahedra, edges with four equivalent Ni(2)Al4Ni8 cuboctahedra, edges with eight equivalent Ni(4)Al4Ni8 cuboctahedra,  a faceface with one Al(2)Ni12 cuboctahedra, faces with four equivalent Ni(4)Al4Ni8 cuboctahedra, faces with five equivalent Al(1)Ni12 cuboctahedra, and faces with four equivalent C(1)Ni6 octahedra. In the second Al site, Al(2) is bonded to four equivalent Ni(2) and eight equivalent Ni(4) atoms to form AlNi12 cuboctahedra that share corners with four equivalent Al(2)Ni12 cuboctahedra, corners with eight equivalent Al(1)Ni12 cuboctahedra, edges with sixteen equivalent Ni(4)Al4Ni8 cuboctahedra, faces with two equivalent Al(1)Ni12 cuboctahedra, faces with four equivalent Ni(2)Al4Ni8 cuboctahedra, faces with four equivalent Al(2)Ni12 cuboctahedra, and faces with eight equivalent Ni(4)Al4Ni8 cuboctahedra. C(1) is bonded to two equivalent Ni(1) and four equivalent Ni(3) atoms to form CNi6 octahedra that share corners with eight equivalent Ni(4)Al4Ni8 cuboctahedra, corners with four equivalent C(1)Ni6 octahedra, and faces with eight equivalent Al(1)Ni12 cuboctahedra. The corner-sharing octahedra are not tilted.