Y4C7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one C(2), one C(3), two equivalent C(1), and three equivalent C(4) atoms to form distorted YC7 octahedra that share corners with two equivalent Y(1)C7 octahedra,  a cornercorner with one C(2)Y4C trigonal bipyramid, and edges with five equivalent Y(1)C7 octahedra. The corner-sharing octahedra are not tilted. In the second Y site, Y(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 Y(2) and four equivalent Y(1) atoms to form CY6 octahedra that share corners with two equivalent C(2)Y4C trigonal bipyramids, edges with two equivalent C(1)Y6 octahedra, and edges with four equivalent C(2)Y4C trigonal bipyramids. In the second C site, C(2) is bonded to one Y(1), three equivalent Y(2), and one C(3) atom to form distorted CY4C trigonal bipyramids that share  a cornercorner with one Y(1)C7 octahedra,  a cornercorner with one C(1)Y6 octahedra, corners with six equivalent C(2)Y4C trigonal bipyramids, and edges with two equivalent C(1)Y6 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 Y(1), three equivalent Y(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 Y(2), three equivalent Y(1), and one C(3) atom.
Y4C7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one C(2), one C(3), two equivalent C(1), and three equivalent C(4) atoms to form distorted YC7 octahedra that share corners with two equivalent Y(1)C7 octahedra,  a cornercorner with one C(2)Y4C trigonal bipyramid, and edges with five equivalent Y(1)C7 octahedra. The corner-sharing octahedra are not tilted. The Y(1)-C(2) bond length is 2.49 Å. The Y(1)-C(3) bond length is 2.99 Å. There is one shorter (2.53 Å) and one longer (2.63 Å) Y(1)-C(1) bond length. There are a spread of Y(1)-C(4) bond distances ranging from 2.50-2.70 Å. In the second Y site, Y(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 Y(2)-C(1) bond length is 2.45 Å. There is one shorter (2.59 Å) and one longer (2.85 Å) Y(2)-C(4) bond length. There are a spread of Y(2)-C(2) bond distances ranging from 2.44-2.58 Å. There are a spread of Y(2)-C(3) bond distances ranging from 2.49-2.82 Å. There are four inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Y(2) and four equivalent Y(1) atoms to form CY6 octahedra that share corners with two equivalent C(2)Y4C trigonal bipyramids, edges with two equivalent C(1)Y6 octahedra, and edges with four equivalent C(2)Y4C trigonal bipyramids. In the second C site, C(2) is bonded to one Y(1), three equivalent Y(2), and one C(3) atom to form distorted CY4C trigonal bipyramids that share  a cornercorner with one Y(1)C7 octahedra,  a cornercorner with one C(1)Y6 octahedra, corners with six equivalent C(2)Y4C trigonal bipyramids, and edges with two equivalent C(1)Y6 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 Y(1), three equivalent Y(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 Y(2), three equivalent Y(1), and one C(3) atom.