Tm2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 8-coordinate geometry to one O(1), one O(11), one O(4), one O(9), two equivalent O(13), and two equivalent O(6) atoms. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(12), one O(3), one O(8), two equivalent O(2), and two equivalent O(5) atoms. In the third Tm site, Tm(3) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(11), one O(13), one O(14), one O(6), one O(7), and one O(9) atom. In the fourth Tm site, Tm(4) is bonded in a 8-coordinate geometry to one O(10), one O(14), one O(2), one O(5), one O(7), one O(8), and two equivalent O(12) atoms. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(10), one O(2), one O(3), one O(5), and one O(7) atom to form corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 34-47°. In the second Ti site, Ti(2) is bonded to one O(1), one O(11), one O(4), one O(7), and two equivalent O(6) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 29-47°. In the third Ti site, Ti(3) is bonded to one O(10), one O(12), one O(14), one O(3), one O(8), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 34-52°. In the fourth Ti site, Ti(4) is bonded to one O(11), one O(14), one O(4), one O(9), and two equivalent O(13) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 29-52°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded to one Tm(1), one Tm(3), one Ti(1), and one Ti(2) atom to form distorted OTm2Ti2 tetrahedra that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra,  a cornercorner with one O(2)Tm3Ti tetrahedra,  a cornercorner with one O(5)Tm3Ti tetrahedra, corners with two equivalent O(9)Tm2Ti2 tetrahedra,  an edgeedge with one O(11)Tm2Ti2 tetrahedra, and  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid. In the second O site, O(2) is bonded to one Tm(4), two equivalent Tm(2), and one Ti(1) atom to form distorted OTm3Ti tetrahedra that share  a cornercorner with one O(1)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti tetrahedra, corners with two equivalent O(12)Tm3Ti trigonal pyramids, edges with three equivalent O(5)Tm3Ti tetrahedra,  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid, and  an edgeedge with one O(12)Tm3Ti trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Tm(2), one Ti(1), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Tm(1), one Ti(2), and one Ti(4) atom. In the fifth O site, O(5) is bonded to one Tm(4), two equivalent Tm(2), and one Ti(1) atom to form distorted OTm3Ti tetrahedra that share  a cornercorner with one O(1)Tm2Ti2 tetrahedra, corners with two equivalent O(5)Tm3Ti tetrahedra, corners with two equivalent O(10)Tm2Ti2 trigonal pyramids, corners with four equivalent O(12)Tm3Ti trigonal pyramids, and edges with three equivalent O(2)Tm3Ti tetrahedra. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Tm(3), two equivalent Tm(1), and two equivalent Ti(2) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Tm(3), one Tm(4), one Ti(1), and one Ti(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Tm(2), one Tm(4), and one Ti(3) atom. In the ninth O site, O(9) is bonded to one Tm(1), one Tm(3), one Ti(3), and one Ti(4) atom to form distorted OTm2Ti2 tetrahedra that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra, corners with two equivalent O(1)Tm2Ti2 tetrahedra,  a cornercorner with one O(12)Tm3Ti trigonal pyramid,  an edgeedge with one O(11)Tm2Ti2 tetrahedra, and  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid. In the tenth O site, O(10) is bonded to one Tm(3), one Tm(4), one Ti(1), and one Ti(3) atom to form distorted OTm2Ti2 trigonal pyramids that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra, corners with two equivalent O(5)Tm3Ti tetrahedra, corners with three equivalent O(12)Tm3Ti trigonal pyramids,  an edgeedge with one O(1)Tm2Ti2 tetrahedra,  an edgeedge with one O(9)Tm2Ti2 tetrahedra, and  an edgeedge with one O(2)Tm3Ti tetrahedra. In the eleventh O site, O(11) is bonded to one Tm(1), one Tm(3), one Ti(2), and one Ti(4) atom to form a mixture of distorted edge and corner-sharing OTm2Ti2 tetrahedra. In the twelfth O site, O(12) is bonded to one Tm(2), two equivalent Tm(4), and one Ti(3) atom to form distorted OTm3Ti trigonal pyramids that share  a cornercorner with one O(9)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti tetrahedra, corners with four equivalent O(5)Tm3Ti tetrahedra, corners with two equivalent O(12)Tm3Ti trigonal pyramids, corners with three equivalent O(10)Tm2Ti2 trigonal pyramids, and  an edgeedge with one O(2)Tm3Ti tetrahedra. In the thirteenth O site, O(13) is bonded in a 5-coordinate geometry to one Tm(3), two equivalent Tm(1), and two equivalent Ti(4) atoms. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Tm(3), one Tm(4), one Ti(3), and one Ti(4) atom.
Tm2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 8-coordinate geometry to one O(1), one O(11), one O(4), one O(9), two equivalent O(13), and two equivalent O(6) atoms. The Tm(1)-O(1) bond length is 2.23 Å. The Tm(1)-O(11) bond length is 2.20 Å. The Tm(1)-O(4) bond length is 2.24 Å. The Tm(1)-O(9) bond length is 2.20 Å. There is one shorter (2.37 Å) and one longer (2.62 Å) Tm(1)-O(13) bond length. There is one shorter (2.39 Å) and one longer (2.67 Å) Tm(1)-O(6) bond length. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(12), one O(3), one O(8), two equivalent O(2), and two equivalent O(5) atoms. The Tm(2)-O(12) bond length is 2.39 Å. The Tm(2)-O(3) bond length is 2.24 Å. The Tm(2)-O(8) bond length is 2.17 Å. There is one shorter (2.25 Å) and one longer (2.27 Å) Tm(2)-O(2) bond length. There is one shorter (2.27 Å) and one longer (2.39 Å) Tm(2)-O(5) bond length. In the third Tm site, Tm(3) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(11), one O(13), one O(14), one O(6), one O(7), and one O(9) atom. The Tm(3)-O(1) bond length is 2.43 Å. The Tm(3)-O(10) bond length is 2.29 Å. The Tm(3)-O(11) bond length is 2.18 Å. The Tm(3)-O(13) bond length is 2.26 Å. The Tm(3)-O(14) bond length is 2.37 Å. The Tm(3)-O(6) bond length is 2.27 Å. The Tm(3)-O(7) bond length is 2.39 Å. The Tm(3)-O(9) bond length is 2.37 Å. In the fourth Tm site, Tm(4) is bonded in a 8-coordinate geometry to one O(10), one O(14), one O(2), one O(5), one O(7), one O(8), and two equivalent O(12) atoms. The Tm(4)-O(10) bond length is 2.32 Å. The Tm(4)-O(14) bond length is 2.48 Å. The Tm(4)-O(2) bond length is 2.43 Å. The Tm(4)-O(5) bond length is 2.30 Å. The Tm(4)-O(7) bond length is 2.59 Å. The Tm(4)-O(8) bond length is 2.28 Å. There is one shorter (2.32 Å) and one longer (2.41 Å) Tm(4)-O(12) bond length. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(10), one O(2), one O(3), one O(5), and one O(7) atom to form corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 34-47°. The Ti(1)-O(1) bond length is 2.01 Å. The Ti(1)-O(10) bond length is 2.01 Å. The Ti(1)-O(2) bond length is 1.88 Å. The Ti(1)-O(3) bond length is 1.90 Å. The Ti(1)-O(5) bond length is 1.86 Å. The Ti(1)-O(7) bond length is 2.14 Å. In the second Ti site, Ti(2) is bonded to one O(1), one O(11), one O(4), one O(7), and two equivalent O(6) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 29-47°. The Ti(2)-O(1) bond length is 1.93 Å. The Ti(2)-O(11) bond length is 2.01 Å. The Ti(2)-O(4) bond length is 1.91 Å. The Ti(2)-O(7) bond length is 1.82 Å. There is one shorter (1.97 Å) and one longer (2.26 Å) Ti(2)-O(6) bond length. In the third Ti site, Ti(3) is bonded to one O(10), one O(12), one O(14), one O(3), one O(8), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 34-52°. The Ti(3)-O(10) bond length is 2.00 Å. The Ti(3)-O(12) bond length is 1.91 Å. The Ti(3)-O(14) bond length is 2.20 Å. The Ti(3)-O(3) bond length is 1.91 Å. The Ti(3)-O(8) bond length is 1.78 Å. The Ti(3)-O(9) bond length is 2.09 Å. In the fourth Ti site, Ti(4) is bonded to one O(11), one O(14), one O(4), one O(9), and two equivalent O(13) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 29-52°. The Ti(4)-O(11) bond length is 2.01 Å. The Ti(4)-O(14) bond length is 1.82 Å. The Ti(4)-O(4) bond length is 1.92 Å. The Ti(4)-O(9) bond length is 1.91 Å. There is one shorter (1.97 Å) and one longer (2.34 Å) Ti(4)-O(13) bond length. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded to one Tm(1), one Tm(3), one Ti(1), and one Ti(2) atom to form distorted OTm2Ti2 tetrahedra that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra,  a cornercorner with one O(2)Tm3Ti tetrahedra,  a cornercorner with one O(5)Tm3Ti tetrahedra, corners with two equivalent O(9)Tm2Ti2 tetrahedra,  an edgeedge with one O(11)Tm2Ti2 tetrahedra, and  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid. In the second O site, O(2) is bonded to one Tm(4), two equivalent Tm(2), and one Ti(1) atom to form distorted OTm3Ti tetrahedra that share  a cornercorner with one O(1)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti tetrahedra, corners with two equivalent O(12)Tm3Ti trigonal pyramids, edges with three equivalent O(5)Tm3Ti tetrahedra,  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid, and  an edgeedge with one O(12)Tm3Ti trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Tm(2), one Ti(1), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Tm(1), one Ti(2), and one Ti(4) atom. In the fifth O site, O(5) is bonded to one Tm(4), two equivalent Tm(2), and one Ti(1) atom to form distorted OTm3Ti tetrahedra that share  a cornercorner with one O(1)Tm2Ti2 tetrahedra, corners with two equivalent O(5)Tm3Ti tetrahedra, corners with two equivalent O(10)Tm2Ti2 trigonal pyramids, corners with four equivalent O(12)Tm3Ti trigonal pyramids, and edges with three equivalent O(2)Tm3Ti tetrahedra. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Tm(3), two equivalent Tm(1), and two equivalent Ti(2) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Tm(3), one Tm(4), one Ti(1), and one Ti(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Tm(2), one Tm(4), and one Ti(3) atom. In the ninth O site, O(9) is bonded to one Tm(1), one Tm(3), one Ti(3), and one Ti(4) atom to form distorted OTm2Ti2 tetrahedra that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra, corners with two equivalent O(1)Tm2Ti2 tetrahedra,  a cornercorner with one O(12)Tm3Ti trigonal pyramid,  an edgeedge with one O(11)Tm2Ti2 tetrahedra, and  an edgeedge with one O(10)Tm2Ti2 trigonal pyramid. In the tenth O site, O(10) is bonded to one Tm(3), one Tm(4), one Ti(1), and one Ti(3) atom to form distorted OTm2Ti2 trigonal pyramids that share  a cornercorner with one O(11)Tm2Ti2 tetrahedra, corners with two equivalent O(5)Tm3Ti tetrahedra, corners with three equivalent O(12)Tm3Ti trigonal pyramids,  an edgeedge with one O(1)Tm2Ti2 tetrahedra,  an edgeedge with one O(9)Tm2Ti2 tetrahedra, and  an edgeedge with one O(2)Tm3Ti tetrahedra. In the eleventh O site, O(11) is bonded to one Tm(1), one Tm(3), one Ti(2), and one Ti(4) atom to form a mixture of distorted edge and corner-sharing OTm2Ti2 tetrahedra. In the twelfth O site, O(12) is bonded to one Tm(2), two equivalent Tm(4), and one Ti(3) atom to form distorted OTm3Ti trigonal pyramids that share  a cornercorner with one O(9)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti tetrahedra, corners with four equivalent O(5)Tm3Ti tetrahedra, corners with two equivalent O(12)Tm3Ti trigonal pyramids, corners with three equivalent O(10)Tm2Ti2 trigonal pyramids, and  an edgeedge with one O(2)Tm3Ti tetrahedra. In the thirteenth O site, O(13) is bonded in a 5-coordinate geometry to one Tm(3), two equivalent Tm(1), and two equivalent Ti(4) atoms. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Tm(3), one Tm(4), one Ti(3), and one Ti(4) atom.