MgEr4Ti2O10 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(2), one O(4), and one O(8) atom to form MgO4 tetrahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Ti(2)O4 tetrahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 33-75°. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form distorted ErO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 13-28°. In the second Er site, Er(2) is bonded to one O(1), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Er(4)O6 pentagonal pyramid,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-28°. In the third Er site, Er(3) is bonded to one O(1), one O(10), one O(3), one O(5), one O(7), and one O(9) atom to form distorted ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Er(4)O6 pentagonal pyramid,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Er(4)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 13-16°. In the fourth Er site, Er(4) is bonded to one O(10), one O(3), one O(5), one O(7), one O(8), and one O(9) atom to form distorted ErO6 pentagonal pyramids that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(2)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 11-27°. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(10), one O(3), one O(6), one O(7), and one O(9) atom to form TiO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, and edges with two equivalent Er(4)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 16-17°. In the second Ti site, Ti(2) is bonded to one O(2), one O(5), one O(6), and one O(8) atom to form TiO4 tetrahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Er(4)O6 pentagonal pyramids, and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-73°. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), one Er(2), one Er(3), and one Ti(1) atom to form distorted OEr3Ti trigonal pyramids that share corners with two equivalent O(7)Er4Ti square pyramids, corners with three equivalent O(6)Er2Ti2 tetrahedra,  a cornercorner with one O(9)Er3Ti trigonal pyramid,  an edgeedge with one O(7)Er4Ti square pyramid, edges with two equivalent O(3)Er4Ti square pyramids, and  an edgeedge with one O(9)Er3Ti trigonal pyramid. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1), one Er(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Er(1), one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form OEr4Ti square pyramids that share  a cornercorner with one O(7)Er4Ti square pyramid,  a cornercorner with one O(6)Er2Ti2 tetrahedra, corners with two equivalent O(9)Er3Ti trigonal pyramids, edges with two equivalent O(7)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra,  an edgeedge with one O(9)Er3Ti trigonal pyramid, and edges with two equivalent O(1)Er3Ti trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Er(1), and one Er(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Er(3), one Er(4), and one Ti(2) atom. In the sixth O site, O(6) is bonded to one Er(1), one Er(2), one Ti(1), and one Ti(2) atom to form distorted OEr2Ti2 tetrahedra that share  a cornercorner with one O(3)Er4Ti square pyramid,  a cornercorner with one O(7)Er4Ti square pyramid, corners with three equivalent O(1)Er3Ti trigonal pyramids,  an edgeedge with one O(3)Er4Ti square pyramid,  an edgeedge with one O(7)Er4Ti square pyramid, and  an edgeedge with one O(9)Er3Ti trigonal pyramid. In the seventh O site, O(7) is bonded to one Er(1), one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form OEr4Ti square pyramids that share  a cornercorner with one O(3)Er4Ti square pyramid,  a cornercorner with one O(6)Er2Ti2 tetrahedra, corners with two equivalent O(1)Er3Ti trigonal pyramids, edges with two equivalent O(3)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra,  an edgeedge with one O(1)Er3Ti trigonal pyramid, and edges with two equivalent O(9)Er3Ti trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Er(4), and one Ti(2) atom. In the ninth O site, O(9) is bonded to one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form distorted OEr3Ti trigonal pyramids that share corners with two equivalent O(3)Er4Ti square pyramids,  a cornercorner with one O(1)Er3Ti trigonal pyramid,  an edgeedge with one O(3)Er4Ti square pyramid, edges with two equivalent O(7)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra, and  an edgeedge with one O(1)Er3Ti trigonal pyramid. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Er(3), one Er(4), and one Ti(1) atom.
MgEr4Ti2O10 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(2), one O(4), and one O(8) atom to form MgO4 tetrahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Ti(2)O4 tetrahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 33-75°. The Mg(1)-O(10) bond length is 1.98 Å. The Mg(1)-O(2) bond length is 2.02 Å. The Mg(1)-O(4) bond length is 1.91 Å. The Mg(1)-O(8) bond length is 2.08 Å. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form distorted ErO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 13-28°. The Er(1)-O(1) bond length is 2.20 Å. The Er(1)-O(2) bond length is 2.23 Å. The Er(1)-O(3) bond length is 2.38 Å. The Er(1)-O(4) bond length is 2.09 Å. The Er(1)-O(6) bond length is 2.34 Å. The Er(1)-O(7) bond length is 2.56 Å. In the second Er site, Er(2) is bonded to one O(1), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Er(4)O6 pentagonal pyramid,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Er(4)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-28°. The Er(2)-O(1) bond length is 2.18 Å. The Er(2)-O(3) bond length is 2.38 Å. The Er(2)-O(4) bond length is 2.14 Å. The Er(2)-O(6) bond length is 2.33 Å. The Er(2)-O(7) bond length is 2.34 Å. The Er(2)-O(9) bond length is 2.33 Å. In the third Er site, Er(3) is bonded to one O(1), one O(10), one O(3), one O(5), one O(7), and one O(9) atom to form distorted ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Er(4)O6 pentagonal pyramid,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Er(4)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 13-16°. The Er(3)-O(1) bond length is 2.35 Å. The Er(3)-O(10) bond length is 2.28 Å. The Er(3)-O(3) bond length is 2.33 Å. The Er(3)-O(5) bond length is 2.23 Å. The Er(3)-O(7) bond length is 2.39 Å. The Er(3)-O(9) bond length is 2.19 Å. In the fourth Er site, Er(4) is bonded to one O(10), one O(3), one O(5), one O(7), one O(8), and one O(9) atom to form distorted ErO6 pentagonal pyramids that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(2)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, edges with two equivalent Ti(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 11-27°. The Er(4)-O(10) bond length is 2.36 Å. The Er(4)-O(3) bond length is 2.40 Å. The Er(4)-O(5) bond length is 2.18 Å. The Er(4)-O(7) bond length is 2.28 Å. The Er(4)-O(8) bond length is 2.22 Å. The Er(4)-O(9) bond length is 2.20 Å. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(10), one O(3), one O(6), one O(7), and one O(9) atom to form TiO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, edges with two equivalent Er(3)O6 octahedra, and edges with two equivalent Er(4)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 16-17°. The Ti(1)-O(1) bond length is 2.08 Å. The Ti(1)-O(10) bond length is 2.02 Å. The Ti(1)-O(3) bond length is 2.25 Å. The Ti(1)-O(6) bond length is 2.18 Å. The Ti(1)-O(7) bond length is 2.24 Å. The Ti(1)-O(9) bond length is 2.08 Å. In the second Ti site, Ti(2) is bonded to one O(2), one O(5), one O(6), and one O(8) atom to form TiO4 tetrahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Er(4)O6 pentagonal pyramids, and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-73°. The Ti(2)-O(2) bond length is 1.88 Å. The Ti(2)-O(5) bond length is 1.91 Å. The Ti(2)-O(6) bond length is 1.97 Å. The Ti(2)-O(8) bond length is 1.85 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), one Er(2), one Er(3), and one Ti(1) atom to form distorted OEr3Ti trigonal pyramids that share corners with two equivalent O(7)Er4Ti square pyramids, corners with three equivalent O(6)Er2Ti2 tetrahedra,  a cornercorner with one O(9)Er3Ti trigonal pyramid,  an edgeedge with one O(7)Er4Ti square pyramid, edges with two equivalent O(3)Er4Ti square pyramids, and  an edgeedge with one O(9)Er3Ti trigonal pyramid. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1), one Er(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Er(1), one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form OEr4Ti square pyramids that share  a cornercorner with one O(7)Er4Ti square pyramid,  a cornercorner with one O(6)Er2Ti2 tetrahedra, corners with two equivalent O(9)Er3Ti trigonal pyramids, edges with two equivalent O(7)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra,  an edgeedge with one O(9)Er3Ti trigonal pyramid, and edges with two equivalent O(1)Er3Ti trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Er(1), and one Er(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Er(3), one Er(4), and one Ti(2) atom. In the sixth O site, O(6) is bonded to one Er(1), one Er(2), one Ti(1), and one Ti(2) atom to form distorted OEr2Ti2 tetrahedra that share  a cornercorner with one O(3)Er4Ti square pyramid,  a cornercorner with one O(7)Er4Ti square pyramid, corners with three equivalent O(1)Er3Ti trigonal pyramids,  an edgeedge with one O(3)Er4Ti square pyramid,  an edgeedge with one O(7)Er4Ti square pyramid, and  an edgeedge with one O(9)Er3Ti trigonal pyramid. In the seventh O site, O(7) is bonded to one Er(1), one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form OEr4Ti square pyramids that share  a cornercorner with one O(3)Er4Ti square pyramid,  a cornercorner with one O(6)Er2Ti2 tetrahedra, corners with two equivalent O(1)Er3Ti trigonal pyramids, edges with two equivalent O(3)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra,  an edgeedge with one O(1)Er3Ti trigonal pyramid, and edges with two equivalent O(9)Er3Ti trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Er(4), and one Ti(2) atom. In the ninth O site, O(9) is bonded to one Er(2), one Er(3), one Er(4), and one Ti(1) atom to form distorted OEr3Ti trigonal pyramids that share corners with two equivalent O(3)Er4Ti square pyramids,  a cornercorner with one O(1)Er3Ti trigonal pyramid,  an edgeedge with one O(3)Er4Ti square pyramid, edges with two equivalent O(7)Er4Ti square pyramids,  an edgeedge with one O(6)Er2Ti2 tetrahedra, and  an edgeedge with one O(1)Er3Ti trigonal pyramid. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Er(3), one Er(4), and one Ti(1) atom.