U5Re3C8 crystallizes in the tetragonal P4/mbm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded to two equivalent C(3) and four equivalent C(2) atoms to form UC6 octahedra that share corners with six equivalent Re(1)C5 trigonal bipyramids, edges with two equivalent U(1)C6 octahedra, edges with eight equivalent U(2)C7 pentagonal bipyramids, and edges with two equivalent Re(1)C5 trigonal bipyramids. In the second U site, U(2) is bonded to one C(2), two equivalent C(3), and four equivalent C(1) atoms to form distorted UC7 pentagonal bipyramids that share corners with seven equivalent U(2)C7 pentagonal bipyramids, edges with two equivalent U(1)C6 octahedra, edges with three equivalent U(2)C7 pentagonal bipyramids, edges with four equivalent Re(1)C5 trigonal bipyramids, and faces with two equivalent U(2)C7 pentagonal bipyramids. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one C(3), two equivalent C(1), and two equivalent C(2) atoms to form distorted ReC5 trigonal bipyramids that share corners with three equivalent U(1)C6 octahedra, corners with two equivalent Re(1)C5 trigonal bipyramids,  an edgeedge with one U(1)C6 octahedra, and edges with eight equivalent U(2)C7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 0-9°. In the second Re site, Re(2) is bonded in a square co-planar geometry to four equivalent C(1) atoms. There are three inequivalent C sites. In the first C site, C(1) is bonded to four equivalent U(2), one Re(1), and one Re(2) atom to form CU4Re2 octahedra that share corners with two equivalent C(2)U4Re2 octahedra, corners with four equivalent C(3)U5Re octahedra, corners with six equivalent C(1)U4Re2 octahedra,  an edgeedge with one C(3)U5Re octahedra, edges with two equivalent C(1)U4Re2 octahedra, edges with two equivalent C(2)U4Re2 octahedra,  a faceface with one C(3)U5Re octahedra, and faces with two equivalent C(1)U4Re2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second C site, C(2) is bonded to two equivalent U(1), two equivalent U(2), and two equivalent Re(1) atoms to form CU4Re2 octahedra that share corners with two equivalent C(2)U4Re2 octahedra, corners with two equivalent C(3)U5Re octahedra, corners with four equivalent C(1)U4Re2 octahedra, edges with three equivalent C(2)U4Re2 octahedra, edges with four equivalent C(1)U4Re2 octahedra, and edges with four equivalent C(3)U5Re octahedra. The corner-sharing octahedral tilt angles range from 0-50°. In the third C site, C(3) is bonded to one U(1), four equivalent U(2), and one Re(1) atom to form CU5Re octahedra that share  a cornercorner with one C(3)U5Re octahedra, corners with two equivalent C(2)U4Re2 octahedra, corners with eight equivalent C(1)U4Re2 octahedra, edges with two equivalent C(1)U4Re2 octahedra, edges with two equivalent C(3)U5Re octahedra, edges with four equivalent C(2)U4Re2 octahedra, and faces with two equivalent C(1)U4Re2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.
U5Re3C8 crystallizes in the tetragonal P4/mbm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded to two equivalent C(3) and four equivalent C(2) atoms to form UC6 octahedra that share corners with six equivalent Re(1)C5 trigonal bipyramids, edges with two equivalent U(1)C6 octahedra, edges with eight equivalent U(2)C7 pentagonal bipyramids, and edges with two equivalent Re(1)C5 trigonal bipyramids. Both U(1)-C(3) bond lengths are 2.43 Å. All U(1)-C(2) bond lengths are 2.52 Å. In the second U site, U(2) is bonded to one C(2), two equivalent C(3), and four equivalent C(1) atoms to form distorted UC7 pentagonal bipyramids that share corners with seven equivalent U(2)C7 pentagonal bipyramids, edges with two equivalent U(1)C6 octahedra, edges with three equivalent U(2)C7 pentagonal bipyramids, edges with four equivalent Re(1)C5 trigonal bipyramids, and faces with two equivalent U(2)C7 pentagonal bipyramids. The U(2)-C(2) bond length is 2.53 Å. Both U(2)-C(3) bond lengths are 2.48 Å. There are two shorter (2.45 Å) and two longer (2.54 Å) U(2)-C(1) bond lengths. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one C(3), two equivalent C(1), and two equivalent C(2) atoms to form distorted ReC5 trigonal bipyramids that share corners with three equivalent U(1)C6 octahedra, corners with two equivalent Re(1)C5 trigonal bipyramids,  an edgeedge with one U(1)C6 octahedra, and edges with eight equivalent U(2)C7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 0-9°. The Re(1)-C(3) bond length is 2.32 Å. Both Re(1)-C(1) bond lengths are 2.03 Å. Both Re(1)-C(2) bond lengths are 2.16 Å. In the second Re site, Re(2) is bonded in a square co-planar geometry to four equivalent C(1) atoms. All Re(2)-C(1) bond lengths are 2.06 Å. There are three inequivalent C sites. In the first C site, C(1) is bonded to four equivalent U(2), one Re(1), and one Re(2) atom to form CU4Re2 octahedra that share corners with two equivalent C(2)U4Re2 octahedra, corners with four equivalent C(3)U5Re octahedra, corners with six equivalent C(1)U4Re2 octahedra,  an edgeedge with one C(3)U5Re octahedra, edges with two equivalent C(1)U4Re2 octahedra, edges with two equivalent C(2)U4Re2 octahedra,  a faceface with one C(3)U5Re octahedra, and faces with two equivalent C(1)U4Re2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second C site, C(2) is bonded to two equivalent U(1), two equivalent U(2), and two equivalent Re(1) atoms to form CU4Re2 octahedra that share corners with two equivalent C(2)U4Re2 octahedra, corners with two equivalent C(3)U5Re octahedra, corners with four equivalent C(1)U4Re2 octahedra, edges with three equivalent C(2)U4Re2 octahedra, edges with four equivalent C(1)U4Re2 octahedra, and edges with four equivalent C(3)U5Re octahedra. The corner-sharing octahedral tilt angles range from 0-50°. In the third C site, C(3) is bonded to one U(1), four equivalent U(2), and one Re(1) atom to form CU5Re octahedra that share  a cornercorner with one C(3)U5Re octahedra, corners with two equivalent C(2)U4Re2 octahedra, corners with eight equivalent C(1)U4Re2 octahedra, edges with two equivalent C(1)U4Re2 octahedra, edges with two equivalent C(3)U5Re octahedra, edges with four equivalent C(2)U4Re2 octahedra, and faces with two equivalent C(1)U4Re2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.