Tm2GeO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(1), and three equivalent O(2) atoms. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Ge(1) is bonded in a tetrahedral geometry to one O(1), one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Tm(1) and one Ge(1) atom to form distorted OTm3Ge trigonal pyramids that share corners with two equivalent O(3)Tm3Ge tetrahedra, corners with five equivalent O(2)Tm4 tetrahedra, corners with four equivalent O(1)Tm3Ge trigonal pyramids,  an edgeedge with one O(3)Tm3Ge tetrahedra, edges with two equivalent O(2)Tm4 tetrahedra, and  an edgeedge with one O(1)Tm3Ge trigonal pyramid. In the second O site, O(2) is bonded to one Tm(2) and three equivalent Tm(1) atoms to form OTm4 tetrahedra that share  a cornercorner with one O(3)Tm3Ge tetrahedra, corners with four equivalent O(2)Tm4 tetrahedra, corners with five equivalent O(1)Tm3Ge trigonal pyramids,  an edgeedge with one O(2)Tm4 tetrahedra, edges with two equivalent O(3)Tm3Ge tetrahedra, and edges with two equivalent O(1)Tm3Ge trigonal pyramids. In the third O site, O(3) is bonded to one Tm(1), two equivalent Tm(2), and one Ge(1) atom to form distorted OTm3Ge tetrahedra that share  a cornercorner with one O(2)Tm4 tetrahedra, corners with two equivalent O(3)Tm3Ge tetrahedra, corners with two equivalent O(1)Tm3Ge trigonal pyramids, edges with two equivalent O(2)Tm4 tetrahedra, and  an edgeedge with one O(1)Tm3Ge trigonal pyramid. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ge(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ge(1) atom.
Tm2GeO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(1), and three equivalent O(2) atoms. The Tm(1)-O(3) bond length is 2.28 Å. There are a spread of Tm(1)-O(1) bond distances ranging from 2.33-2.53 Å. There are a spread of Tm(1)-O(2) bond distances ranging from 2.21-2.31 Å. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. The Tm(2)-O(2) bond length is 2.26 Å. There is one shorter (2.24 Å) and one longer (2.40 Å) Tm(2)-O(3) bond length. Both Tm(2)-O(4) bond lengths are 2.35 Å. There is one shorter (2.26 Å) and one longer (2.34 Å) Tm(2)-O(5) bond length. Ge(1) is bonded in a tetrahedral geometry to one O(1), one O(3), one O(4), and one O(5) atom. The Ge(1)-O(1) bond length is 1.80 Å. The Ge(1)-O(3) bond length is 1.82 Å. The Ge(1)-O(4) bond length is 1.73 Å. The Ge(1)-O(5) bond length is 1.76 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Tm(1) and one Ge(1) atom to form distorted OTm3Ge trigonal pyramids that share corners with two equivalent O(3)Tm3Ge tetrahedra, corners with five equivalent O(2)Tm4 tetrahedra, corners with four equivalent O(1)Tm3Ge trigonal pyramids,  an edgeedge with one O(3)Tm3Ge tetrahedra, edges with two equivalent O(2)Tm4 tetrahedra, and  an edgeedge with one O(1)Tm3Ge trigonal pyramid. In the second O site, O(2) is bonded to one Tm(2) and three equivalent Tm(1) atoms to form OTm4 tetrahedra that share  a cornercorner with one O(3)Tm3Ge tetrahedra, corners with four equivalent O(2)Tm4 tetrahedra, corners with five equivalent O(1)Tm3Ge trigonal pyramids,  an edgeedge with one O(2)Tm4 tetrahedra, edges with two equivalent O(3)Tm3Ge tetrahedra, and edges with two equivalent O(1)Tm3Ge trigonal pyramids. In the third O site, O(3) is bonded to one Tm(1), two equivalent Tm(2), and one Ge(1) atom to form distorted OTm3Ge tetrahedra that share  a cornercorner with one O(2)Tm4 tetrahedra, corners with two equivalent O(3)Tm3Ge tetrahedra, corners with two equivalent O(1)Tm3Ge trigonal pyramids, edges with two equivalent O(2)Tm4 tetrahedra, and  an edgeedge with one O(1)Tm3Ge trigonal pyramid. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ge(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ge(1) atom.