LuEr4Ni10(B2C)5 crystallizes in the monoclinic C2/m space group. Lu(1) is bonded in a square co-planar geometry to four equivalent C(2) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a square co-planar geometry to two equivalent C(1) and two equivalent C(3) atoms. In the second Er site, Er(2) is bonded in a rectangular see-saw-like geometry to two equivalent C(1) and two equivalent C(2) atoms. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one B(5) and three equivalent B(1) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(3)Er4B2 octahedra, corners with three equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(1)B4 tetrahedra, edges with two equivalent Ni(1)B4 tetrahedra, and edges with two equivalent Ni(2)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. In the second Ni site, Ni(2) is bonded to one B(1), one B(2), and two equivalent B(5) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(2)Er2Lu2B2 octahedra,  a cornercorner with one C(1)Er4B2 octahedra, corners with two equivalent C(3)Er4B2 octahedra,  a cornercorner with one Ni(1)B4 tetrahedra,  a cornercorner with one Ni(3)B4 tetrahedra, corners with two equivalent Ni(2)B4 tetrahedra, edges with two equivalent Ni(1)B4 tetrahedra, and edges with two equivalent Ni(5)B4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. In the third Ni site, Ni(3) is bonded to one B(2), one B(3), and two equivalent B(4) atoms to form NiB4 tetrahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, edges with two equivalent Ni(4)B4 tetrahedra, and edges with two equivalent Ni(5)B4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. In the fourth Ni site, Ni(4) is bonded to one B(4) and three equivalent B(3) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(1)Er4B2 octahedra, corners with three equivalent C(2)Er2Lu2B2 octahedra,  a cornercorner with one Ni(3)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(4)B4 tetrahedra, edges with two equivalent Ni(3)B4 tetrahedra, and edges with two equivalent Ni(4)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. In the fifth Ni site, Ni(5) is bonded to one B(4), one B(5), and two equivalent B(2) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(1)Er4B2 octahedra,  a cornercorner with one C(3)Er4B2 octahedra, corners with two equivalent C(2)Er2Lu2B2 octahedra,  a cornercorner with one Ni(1)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, edges with two equivalent Ni(2)B4 tetrahedra, and edges with two equivalent Ni(3)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. There are five inequivalent B sites. In the first B site, B(3) is bonded in a distorted single-bond geometry to one Ni(3), three equivalent Ni(4), and one C(2) atom. In the second B site, B(4) is bonded in a distorted single-bond geometry to one Ni(4), one Ni(5), two equivalent Ni(3), and one C(1) atom. In the third B site, B(5) is bonded in a distorted single-bond geometry to one Ni(1), one Ni(5), two equivalent Ni(2), and one C(3) atom. In the fourth B site, B(1) is bonded in a distorted single-bond geometry to one Ni(2), three equivalent Ni(1), and one C(1) atom. In the fifth B site, B(2) is bonded in a distorted single-bond geometry to one Ni(2), one Ni(3), two equivalent Ni(5), and one C(2) atom. There are three inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Er(1), two equivalent Er(2), one B(1), and one B(4) atom to form distorted CEr4B2 octahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(3)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, corners with three equivalent Ni(1)B4 tetrahedra,  an edgeedge with one C(2)Er2Lu2B2 octahedra,  an edgeedge with one C(3)Er4B2 octahedra, and edges with two equivalent C(1)Er4B2 octahedra. The corner-sharing octahedra are not tilted. In the second C site, C(2) is bonded to two equivalent Lu(1), two equivalent Er(2), one B(2), and one B(3) atom to form distorted CEr2Lu2B2 octahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, corners with three equivalent Ni(4)B4 tetrahedra,  an edgeedge with one C(1)Er4B2 octahedra, and edges with three equivalent C(2)Er2Lu2B2 octahedra. The corner-sharing octahedra are not tilted. In the third C site, C(3) is bonded to four equivalent Er(1) and two equivalent B(5) atoms to form distorted CEr4B2 octahedra that share corners with four equivalent C(1)Er4B2 octahedra, corners with two equivalent Ni(1)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, corners with four equivalent Ni(2)B4 tetrahedra, edges with two equivalent C(1)Er4B2 octahedra, and edges with two equivalent C(3)Er4B2 octahedra. The corner-sharing octahedra are not tilted.
LuEr4Ni10(B2C)5 crystallizes in the monoclinic C2/m space group. Lu(1) is bonded in a square co-planar geometry to four equivalent C(2) atoms. All Lu(1)-C(2) bond lengths are 2.46 Å. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a square co-planar geometry to two equivalent C(1) and two equivalent C(3) atoms. Both Er(1)-C(1) bond lengths are 2.48 Å. Both Er(1)-C(3) bond lengths are 2.47 Å. In the second Er site, Er(2) is bonded in a rectangular see-saw-like geometry to two equivalent C(1) and two equivalent C(2) atoms. Both Er(2)-C(1) bond lengths are 2.48 Å. Both Er(2)-C(2) bond lengths are 2.49 Å. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one B(5) and three equivalent B(1) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(3)Er4B2 octahedra, corners with three equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(1)B4 tetrahedra, edges with two equivalent Ni(1)B4 tetrahedra, and edges with two equivalent Ni(2)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. The Ni(1)-B(5) bond length is 2.08 Å. All Ni(1)-B(1) bond lengths are 2.08 Å. In the second Ni site, Ni(2) is bonded to one B(1), one B(2), and two equivalent B(5) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(2)Er2Lu2B2 octahedra,  a cornercorner with one C(1)Er4B2 octahedra, corners with two equivalent C(3)Er4B2 octahedra,  a cornercorner with one Ni(1)B4 tetrahedra,  a cornercorner with one Ni(3)B4 tetrahedra, corners with two equivalent Ni(2)B4 tetrahedra, edges with two equivalent Ni(1)B4 tetrahedra, and edges with two equivalent Ni(5)B4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. The Ni(2)-B(1) bond length is 2.08 Å. The Ni(2)-B(2) bond length is 2.08 Å. Both Ni(2)-B(5) bond lengths are 2.08 Å. In the third Ni site, Ni(3) is bonded to one B(2), one B(3), and two equivalent B(4) atoms to form NiB4 tetrahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, edges with two equivalent Ni(4)B4 tetrahedra, and edges with two equivalent Ni(5)B4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. The Ni(3)-B(2) bond length is 2.08 Å. The Ni(3)-B(3) bond length is 2.08 Å. Both Ni(3)-B(4) bond lengths are 2.08 Å. In the fourth Ni site, Ni(4) is bonded to one B(4) and three equivalent B(3) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(1)Er4B2 octahedra, corners with three equivalent C(2)Er2Lu2B2 octahedra,  a cornercorner with one Ni(3)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(4)B4 tetrahedra, edges with two equivalent Ni(3)B4 tetrahedra, and edges with two equivalent Ni(4)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. The Ni(4)-B(4) bond length is 2.08 Å. All Ni(4)-B(3) bond lengths are 2.08 Å. In the fifth Ni site, Ni(5) is bonded to one B(4), one B(5), and two equivalent B(2) atoms to form NiB4 tetrahedra that share  a cornercorner with one C(1)Er4B2 octahedra,  a cornercorner with one C(3)Er4B2 octahedra, corners with two equivalent C(2)Er2Lu2B2 octahedra,  a cornercorner with one Ni(1)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, edges with two equivalent Ni(2)B4 tetrahedra, and edges with two equivalent Ni(3)B4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. The Ni(5)-B(4) bond length is 2.08 Å. The Ni(5)-B(5) bond length is 2.08 Å. Both Ni(5)-B(2) bond lengths are 2.08 Å. There are five inequivalent B sites. In the first B site, B(3) is bonded in a distorted single-bond geometry to one Ni(3), three equivalent Ni(4), and one C(2) atom. The B(3)-C(2) bond length is 1.48 Å. In the second B site, B(4) is bonded in a distorted single-bond geometry to one Ni(4), one Ni(5), two equivalent Ni(3), and one C(1) atom. The B(4)-C(1) bond length is 1.48 Å. In the third B site, B(5) is bonded in a distorted single-bond geometry to one Ni(1), one Ni(5), two equivalent Ni(2), and one C(3) atom. The B(5)-C(3) bond length is 1.48 Å. In the fourth B site, B(1) is bonded in a distorted single-bond geometry to one Ni(2), three equivalent Ni(1), and one C(1) atom. The B(1)-C(1) bond length is 1.48 Å. In the fifth B site, B(2) is bonded in a distorted single-bond geometry to one Ni(2), one Ni(3), two equivalent Ni(5), and one C(2) atom. The B(2)-C(2) bond length is 1.48 Å. There are three inequivalent C sites. In the first C site, C(1) is bonded to two equivalent Er(1), two equivalent Er(2), one B(1), and one B(4) atom to form distorted CEr4B2 octahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(3)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra,  a cornercorner with one Ni(4)B4 tetrahedra,  a cornercorner with one Ni(5)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, corners with three equivalent Ni(1)B4 tetrahedra,  an edgeedge with one C(2)Er2Lu2B2 octahedra,  an edgeedge with one C(3)Er4B2 octahedra, and edges with two equivalent C(1)Er4B2 octahedra. The corner-sharing octahedra are not tilted. In the second C site, C(2) is bonded to two equivalent Lu(1), two equivalent Er(2), one B(2), and one B(3) atom to form distorted CEr2Lu2B2 octahedra that share corners with two equivalent C(2)Er2Lu2B2 octahedra, corners with two equivalent C(1)Er4B2 octahedra,  a cornercorner with one Ni(2)B4 tetrahedra, corners with two equivalent Ni(3)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, corners with three equivalent Ni(4)B4 tetrahedra,  an edgeedge with one C(1)Er4B2 octahedra, and edges with three equivalent C(2)Er2Lu2B2 octahedra. The corner-sharing octahedra are not tilted. In the third C site, C(3) is bonded to four equivalent Er(1) and two equivalent B(5) atoms to form distorted CEr4B2 octahedra that share corners with four equivalent C(1)Er4B2 octahedra, corners with two equivalent Ni(1)B4 tetrahedra, corners with two equivalent Ni(5)B4 tetrahedra, corners with four equivalent Ni(2)B4 tetrahedra, edges with two equivalent C(1)Er4B2 octahedra, and edges with two equivalent C(3)Er4B2 octahedra. The corner-sharing octahedra are not tilted.