Er12(OsC3)5 crystallizes in the hexagonal P-62m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a rectangular see-saw-like geometry to two equivalent C(2) and two equivalent C(4) atoms. In the second Er site, Er(2) is bonded to one C(1), one C(2), one C(3), and two equivalent C(4) atoms to form distorted ErC5 square pyramids that share  a cornercorner with one C(1)Er4OsC octahedra, corners with three equivalent Er(2)C5 square pyramids,  a cornercorner with one C(3)Er4C trigonal bipyramid, and  an edgeedge with one Er(2)C5 square pyramid. The corner-sharing octahedral tilt angles are 42°. In the third Er site, Er(3) is bonded in a 8-coordinate geometry to two equivalent C(1), two equivalent C(3), and four equivalent C(4) atoms. There are two inequivalent Os sites. In the first Os site, Os(1) is bonded in a 3-coordinate geometry to one C(1) and two equivalent C(2) atoms. In the second Os site, Os(2) is bonded in a trigonal planar geometry to three equivalent C(4) atoms. There are four inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Er(2), two equivalent Er(3), one Os(1), and one C(3) atom to form distorted CEr4OsC octahedra that share corners with two equivalent C(1)Er4OsC octahedra, corners with four equivalent C(4)Er5Os octahedra, corners with two equivalent Er(2)C5 square pyramids, corners with four equivalent C(3)Er4C trigonal bipyramids, edges with two equivalent C(2)Er4Os2 octahedra, edges with four equivalent C(4)Er5Os octahedra, and  an edgeedge with one C(3)Er4C trigonal bipyramid. The corner-sharing octahedral tilt angles range from 45-73°. In the second C site, C(2) is bonded to two equivalent Er(1), two equivalent Er(2), and two equivalent Os(1) atoms to form CEr4Os2 octahedra that share corners with four equivalent C(2)Er4Os2 octahedra, edges with two equivalent C(1)Er4OsC octahedra, edges with four equivalent C(4)Er5Os octahedra, and  an edgeedge with one C(3)Er4C trigonal bipyramid. The corner-sharing octahedral tilt angles range from 2-34°. In the third C site, C(3) is bonded to two equivalent Er(2), two equivalent Er(3), and one C(1) atom to form distorted CEr4C trigonal bipyramids that share corners with four equivalent C(1)Er4OsC octahedra, corners with four equivalent C(4)Er5Os octahedra, corners with two equivalent Er(2)C5 square pyramids, corners with two equivalent C(3)Er4C trigonal bipyramids,  an edgeedge with one C(2)Er4Os2 octahedra,  an edgeedge with one C(1)Er4OsC octahedra, and edges with four equivalent C(4)Er5Os octahedra. The corner-sharing octahedral tilt angles range from 8-87°. In the fourth C site, C(4) is bonded to one Er(1), two equivalent Er(2), two equivalent Er(3), and one Os(2) atom to form CEr5Os octahedra that share corners with two equivalent C(1)Er4OsC octahedra, corners with five equivalent C(4)Er5Os octahedra, corners with two equivalent C(3)Er4C trigonal bipyramids, edges with two equivalent C(2)Er4Os2 octahedra, edges with two equivalent C(1)Er4OsC octahedra, edges with three equivalent C(4)Er5Os octahedra, and edges with two equivalent C(3)Er4C trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-73°.
Er12(OsC3)5 crystallizes in the hexagonal P-62m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a rectangular see-saw-like geometry to two equivalent C(2) and two equivalent C(4) atoms. Both Er(1)-C(2) bond lengths are 2.51 Å. Both Er(1)-C(4) bond lengths are 2.47 Å. In the second Er site, Er(2) is bonded to one C(1), one C(2), one C(3), and two equivalent C(4) atoms to form distorted ErC5 square pyramids that share  a cornercorner with one C(1)Er4OsC octahedra, corners with three equivalent Er(2)C5 square pyramids,  a cornercorner with one C(3)Er4C trigonal bipyramid, and  an edgeedge with one Er(2)C5 square pyramid. The corner-sharing octahedral tilt angles are 42°. The Er(2)-C(1) bond length is 2.52 Å. The Er(2)-C(2) bond length is 2.35 Å. The Er(2)-C(3) bond length is 2.50 Å. Both Er(2)-C(4) bond lengths are 2.51 Å. In the third Er site, Er(3) is bonded in a 8-coordinate geometry to two equivalent C(1), two equivalent C(3), and four equivalent C(4) atoms. Both Er(3)-C(1) bond lengths are 2.72 Å. Both Er(3)-C(3) bond lengths are 2.53 Å. There are two shorter (2.65 Å) and two longer (2.85 Å) Er(3)-C(4) bond lengths. There are two inequivalent Os sites. In the first Os site, Os(1) is bonded in a 3-coordinate geometry to one C(1) and two equivalent C(2) atoms. The Os(1)-C(1) bond length is 1.87 Å. Both Os(1)-C(2) bond lengths are 2.03 Å. In the second Os site, Os(2) is bonded in a trigonal planar geometry to three equivalent C(4) atoms. All Os(2)-C(4) bond lengths are 1.92 Å. There are four inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Er(2), two equivalent Er(3), one Os(1), and one C(3) atom to form distorted CEr4OsC octahedra that share corners with two equivalent C(1)Er4OsC octahedra, corners with four equivalent C(4)Er5Os octahedra, corners with two equivalent Er(2)C5 square pyramids, corners with four equivalent C(3)Er4C trigonal bipyramids, edges with two equivalent C(2)Er4Os2 octahedra, edges with four equivalent C(4)Er5Os octahedra, and  an edgeedge with one C(3)Er4C trigonal bipyramid. The corner-sharing octahedral tilt angles range from 45-73°. The C(1)-C(3) bond length is 1.34 Å. In the second C site, C(2) is bonded to two equivalent Er(1), two equivalent Er(2), and two equivalent Os(1) atoms to form CEr4Os2 octahedra that share corners with four equivalent C(2)Er4Os2 octahedra, edges with two equivalent C(1)Er4OsC octahedra, edges with four equivalent C(4)Er5Os octahedra, and  an edgeedge with one C(3)Er4C trigonal bipyramid. The corner-sharing octahedral tilt angles range from 2-34°. In the third C site, C(3) is bonded to two equivalent Er(2), two equivalent Er(3), and one C(1) atom to form distorted CEr4C trigonal bipyramids that share corners with four equivalent C(1)Er4OsC octahedra, corners with four equivalent C(4)Er5Os octahedra, corners with two equivalent Er(2)C5 square pyramids, corners with two equivalent C(3)Er4C trigonal bipyramids,  an edgeedge with one C(2)Er4Os2 octahedra,  an edgeedge with one C(1)Er4OsC octahedra, and edges with four equivalent C(4)Er5Os octahedra. The corner-sharing octahedral tilt angles range from 8-87°. In the fourth C site, C(4) is bonded to one Er(1), two equivalent Er(2), two equivalent Er(3), and one Os(2) atom to form CEr5Os octahedra that share corners with two equivalent C(1)Er4OsC octahedra, corners with five equivalent C(4)Er5Os octahedra, corners with two equivalent C(3)Er4C trigonal bipyramids, edges with two equivalent C(2)Er4Os2 octahedra, edges with two equivalent C(1)Er4OsC octahedra, edges with three equivalent C(4)Er5Os octahedra, and edges with two equivalent C(3)Er4C trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-73°.