Ho4C7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one C(2), one C(3), two equivalent C(1), and three equivalent C(4) atoms to form distorted HoC7 octahedra that share corners with two equivalent Ho(1)C7 octahedra,  a cornercorner with one C(2)Ho4C trigonal bipyramid, and edges with five equivalent Ho(1)C7 octahedra. The corner-sharing octahedra are not tilted. In the second Ho site, Ho(2) is bonded in a 9-coordinate geometry to one C(1), two equivalent C(4), three equivalent C(2), and three equivalent C(3) atoms. There are four inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Ho(2) and four equivalent Ho(1) atoms to form CHo6 octahedra that share corners with two equivalent C(2)Ho4C trigonal bipyramids, edges with two equivalent C(1)Ho6 octahedra, and edges with four equivalent C(2)Ho4C trigonal bipyramids. In the second C site, C(2) is bonded to one Ho(1), three equivalent Ho(2), and one C(3) atom to form distorted CHo4C trigonal bipyramids that share  a cornercorner with one Ho(1)C7 octahedra,  a cornercorner with one C(1)Ho6 octahedra, corners with six equivalent C(2)Ho4C trigonal bipyramids, and edges with two equivalent C(1)Ho6 octahedra. The corner-sharing octahedral tilt angles range from 33-61°. In the third C site, C(3) is bonded in a 6-coordinate geometry to one Ho(1), three equivalent Ho(2), one C(2), and one C(4) atom. In the fourth C site, C(4) is bonded in a 5-coordinate geometry to two equivalent Ho(2), three equivalent Ho(1), and one C(3) atom.
Ho4C7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one C(2), one C(3), two equivalent C(1), and three equivalent C(4) atoms to form distorted HoC7 octahedra that share corners with two equivalent Ho(1)C7 octahedra,  a cornercorner with one C(2)Ho4C trigonal bipyramid, and edges with five equivalent Ho(1)C7 octahedra. The corner-sharing octahedra are not tilted. The Ho(1)-C(2) bond length is 2.46 Å. The Ho(1)-C(3) bond length is 2.97 Å. There is one shorter (2.51 Å) and one longer (2.61 Å) Ho(1)-C(1) bond length. There are a spread of Ho(1)-C(4) bond distances ranging from 2.47-2.66 Å. In the second Ho site, Ho(2) is bonded in a 9-coordinate geometry to one C(1), two equivalent C(4), three equivalent C(2), and three equivalent C(3) atoms. The Ho(2)-C(1) bond length is 2.43 Å. There is one shorter (2.57 Å) and one longer (2.83 Å) Ho(2)-C(4) bond length. There are a spread of Ho(2)-C(2) bond distances ranging from 2.41-2.57 Å. There are a spread of Ho(2)-C(3) bond distances ranging from 2.47-2.79 Å. There are four inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Ho(2) and four equivalent Ho(1) atoms to form CHo6 octahedra that share corners with two equivalent C(2)Ho4C trigonal bipyramids, edges with two equivalent C(1)Ho6 octahedra, and edges with four equivalent C(2)Ho4C trigonal bipyramids. In the second C site, C(2) is bonded to one Ho(1), three equivalent Ho(2), and one C(3) atom to form distorted CHo4C trigonal bipyramids that share  a cornercorner with one Ho(1)C7 octahedra,  a cornercorner with one C(1)Ho6 octahedra, corners with six equivalent C(2)Ho4C trigonal bipyramids, and edges with two equivalent C(1)Ho6 octahedra. The corner-sharing octahedral tilt angles range from 33-61°. The C(2)-C(3) bond length is 1.32 Å. In the third C site, C(3) is bonded in a 6-coordinate geometry to one Ho(1), three equivalent Ho(2), one C(2), and one C(4) atom. The C(3)-C(4) bond length is 1.33 Å. In the fourth C site, C(4) is bonded in a 5-coordinate geometry to two equivalent Ho(2), three equivalent Ho(1), and one C(3) atom.