Er15Fe8C25 crystallizes in the trigonal P3 space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded in a 5-coordinate geometry to one C(5), one C(6), one C(7), one C(8), and one C(9) atom. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to one C(7), two equivalent C(1), two equivalent C(4), and two equivalent C(8) atoms. In the third Er site, Er(3) is bonded in a 5-coordinate geometry to one C(8), two equivalent C(2), two equivalent C(3), and two equivalent C(7) atoms. In the fourth Er site, Er(4) is bonded in a 8-coordinate geometry to one C(1), one C(5), one C(6), one C(7), two equivalent C(2), and two equivalent C(3) atoms. In the fifth Er site, Er(5) is bonded to one C(2), one C(5), one C(6), one C(8), two equivalent C(1), and two equivalent C(4) atoms to form distorted ErC8 hexagonal bipyramids that share corners with four equivalent Er(5)C8 hexagonal bipyramids,  a cornercorner with one C(1)Er5C octahedra, and  a cornercorner with one C(2)Er5C octahedra. The corner-sharing octahedral tilt angles range from 107-113°. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted T-shaped geometry to one C(5), one C(6), and one C(9) atom. In the second Fe site, Fe(2) is bonded in a trigonal planar geometry to three equivalent C(3) atoms. In the third Fe site, Fe(3) is bonded in a trigonal planar geometry to three equivalent C(4) atoms. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to one C(5), one C(6), one C(7), and one C(8) atom. There are nine inequivalent C sites. In the first C site, C(4) is bonded in a 6-coordinate geometry to two equivalent Er(2), two equivalent Er(5), one Fe(3), and one C(8) atom. In the second C site, C(5) is bonded in a 4-coordinate geometry to one Er(1), one Er(4), one Er(5), one Fe(1), one Fe(4), and one C(1) atom. In the third C site, C(6) is bonded in a 4-coordinate geometry to one Er(1), one Er(4), one Er(5), one Fe(1), one Fe(4), and one C(2) atom. In the fourth C site, C(7) is bonded in a 7-coordinate geometry to one Er(1), one Er(2), one Er(4), two equivalent Er(3), one Fe(4), and one C(3) atom. In the fifth C site, C(8) is bonded in a 7-coordinate geometry to one Er(1), one Er(3), one Er(5), two equivalent Er(2), one Fe(4), and one C(4) atom. In the sixth C site, C(9) is bonded in an octahedral geometry to three equivalent Er(1) and three equivalent Fe(1) atoms. In the seventh C site, C(1) is bonded to one Er(4), two equivalent Er(2), two equivalent Er(5), and one C(5) atom to form CEr5C octahedra that share  a cornercorner with one Er(5)C8 hexagonal bipyramid, corners with four equivalent C(1)Er5C octahedra, and edges with two equivalent C(2)Er5C octahedra. The corner-sharing octahedral tilt angles range from 7-33°. In the eighth C site, C(2) is bonded to one Er(5), two equivalent Er(3), two equivalent Er(4), and one C(6) atom to form CEr5C octahedra that share  a cornercorner with one Er(5)C8 hexagonal bipyramid, corners with four equivalent C(2)Er5C octahedra, and edges with two equivalent C(1)Er5C octahedra. The corner-sharing octahedral tilt angles range from 7-33°. In the ninth C site, C(3) is bonded in a 6-coordinate geometry to two equivalent Er(3), two equivalent Er(4), one Fe(2), and one C(7) atom.
Er15Fe8C25 crystallizes in the trigonal P3 space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded in a 5-coordinate geometry to one C(5), one C(6), one C(7), one C(8), and one C(9) atom. The Er(1)-C(5) bond length is 2.52 Å. The Er(1)-C(6) bond length is 2.52 Å. The Er(1)-C(7) bond length is 2.71 Å. The Er(1)-C(8) bond length is 2.71 Å. The Er(1)-C(9) bond length is 2.42 Å. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to one C(7), two equivalent C(1), two equivalent C(4), and two equivalent C(8) atoms. The Er(2)-C(7) bond length is 2.47 Å. There is one shorter (2.41 Å) and one longer (2.52 Å) Er(2)-C(1) bond length. There is one shorter (2.53 Å) and one longer (2.55 Å) Er(2)-C(4) bond length. There is one shorter (2.72 Å) and one longer (2.87 Å) Er(2)-C(8) bond length. In the third Er site, Er(3) is bonded in a 5-coordinate geometry to one C(8), two equivalent C(2), two equivalent C(3), and two equivalent C(7) atoms. The Er(3)-C(8) bond length is 2.47 Å. There is one shorter (2.40 Å) and one longer (2.51 Å) Er(3)-C(2) bond length. There is one shorter (2.53 Å) and one longer (2.56 Å) Er(3)-C(3) bond length. There is one shorter (2.72 Å) and one longer (2.88 Å) Er(3)-C(7) bond length. In the fourth Er site, Er(4) is bonded in a 8-coordinate geometry to one C(1), one C(5), one C(6), one C(7), two equivalent C(2), and two equivalent C(3) atoms. The Er(4)-C(1) bond length is 2.45 Å. The Er(4)-C(5) bond length is 2.65 Å. The Er(4)-C(6) bond length is 2.55 Å. The Er(4)-C(7) bond length is 2.44 Å. There is one shorter (2.50 Å) and one longer (2.58 Å) Er(4)-C(2) bond length. There is one shorter (2.48 Å) and one longer (2.55 Å) Er(4)-C(3) bond length. In the fifth Er site, Er(5) is bonded to one C(2), one C(5), one C(6), one C(8), two equivalent C(1), and two equivalent C(4) atoms to form distorted ErC8 hexagonal bipyramids that share corners with four equivalent Er(5)C8 hexagonal bipyramids,  a cornercorner with one C(1)Er5C octahedra, and  a cornercorner with one C(2)Er5C octahedra. The corner-sharing octahedral tilt angles range from 107-113°. The Er(5)-C(2) bond length is 2.45 Å. The Er(5)-C(5) bond length is 2.53 Å. The Er(5)-C(6) bond length is 2.63 Å. The Er(5)-C(8) bond length is 2.44 Å. There is one shorter (2.50 Å) and one longer (2.58 Å) Er(5)-C(1) bond length. There is one shorter (2.48 Å) and one longer (2.55 Å) Er(5)-C(4) bond length. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted T-shaped geometry to one C(5), one C(6), and one C(9) atom. The Fe(1)-C(5) bond length is 1.95 Å. The Fe(1)-C(6) bond length is 1.98 Å. The Fe(1)-C(9) bond length is 1.92 Å. In the second Fe site, Fe(2) is bonded in a trigonal planar geometry to three equivalent C(3) atoms. All Fe(2)-C(3) bond lengths are 1.83 Å. In the third Fe site, Fe(3) is bonded in a trigonal planar geometry to three equivalent C(4) atoms. All Fe(3)-C(4) bond lengths are 1.83 Å. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to one C(5), one C(6), one C(7), and one C(8) atom. The Fe(4)-C(5) bond length is 2.19 Å. The Fe(4)-C(6) bond length is 2.22 Å. The Fe(4)-C(7) bond length is 1.92 Å. The Fe(4)-C(8) bond length is 1.92 Å. There are nine inequivalent C sites. In the first C site, C(4) is bonded in a 6-coordinate geometry to two equivalent Er(2), two equivalent Er(5), one Fe(3), and one C(8) atom. The C(4)-C(8) bond length is 1.36 Å. In the second C site, C(5) is bonded in a 4-coordinate geometry to one Er(1), one Er(4), one Er(5), one Fe(1), one Fe(4), and one C(1) atom. The C(5)-C(1) bond length is 1.39 Å. In the third C site, C(6) is bonded in a 4-coordinate geometry to one Er(1), one Er(4), one Er(5), one Fe(1), one Fe(4), and one C(2) atom. The C(6)-C(2) bond length is 1.39 Å. In the fourth C site, C(7) is bonded in a 7-coordinate geometry to one Er(1), one Er(2), one Er(4), two equivalent Er(3), one Fe(4), and one C(3) atom. The C(7)-C(3) bond length is 1.36 Å. In the fifth C site, C(8) is bonded in a 7-coordinate geometry to one Er(1), one Er(3), one Er(5), two equivalent Er(2), one Fe(4), and one C(4) atom. In the sixth C site, C(9) is bonded in an octahedral geometry to three equivalent Er(1) and three equivalent Fe(1) atoms. In the seventh C site, C(1) is bonded to one Er(4), two equivalent Er(2), two equivalent Er(5), and one C(5) atom to form CEr5C octahedra that share  a cornercorner with one Er(5)C8 hexagonal bipyramid, corners with four equivalent C(1)Er5C octahedra, and edges with two equivalent C(2)Er5C octahedra. The corner-sharing octahedral tilt angles range from 7-33°. In the eighth C site, C(2) is bonded to one Er(5), two equivalent Er(3), two equivalent Er(4), and one C(6) atom to form CEr5C octahedra that share  a cornercorner with one Er(5)C8 hexagonal bipyramid, corners with four equivalent C(2)Er5C octahedra, and edges with two equivalent C(1)Er5C octahedra. The corner-sharing octahedral tilt angles range from 7-33°. In the ninth C site, C(3) is bonded in a 6-coordinate geometry to two equivalent Er(3), two equivalent Er(4), one Fe(2), and one C(7) atom.