Gd4TiSe4O4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 3-coordinate geometry to one Se(2), four equivalent Se(1), one O(1), and two equivalent O(2) atoms. In the second Gd site, Gd(2) is bonded in a 4-coordinate geometry to two equivalent Se(1), two equivalent Se(2), one O(2), and three equivalent O(1) atoms. Ti(1) is bonded in a distorted linear geometry to four equivalent Se(2) and two equivalent O(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Gd(2) and four equivalent Gd(1) atoms. In the second Se site, Se(2) is bonded in a distorted pentagonal planar geometry to one Gd(1), two equivalent Gd(2), and two equivalent Ti(1) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Gd(1) and three equivalent Gd(2) atoms to form OGd4 tetrahedra that share  a cornercorner with one O(2)Gd3Ti tetrahedra, corners with two equivalent O(1)Gd4 tetrahedra, edges with two equivalent O(2)Gd3Ti tetrahedra, and edges with two equivalent O(1)Gd4 tetrahedra. In the second O site, O(2) is bonded to one Gd(2), two equivalent Gd(1), and one Ti(1) atom to form distorted OGd3Ti tetrahedra that share  a cornercorner with one O(1)Gd4 tetrahedra, corners with three equivalent O(2)Gd3Ti tetrahedra, and edges with two equivalent O(1)Gd4 tetrahedra.
Gd4TiSe4O4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 3-coordinate geometry to one Se(2), four equivalent Se(1), one O(1), and two equivalent O(2) atoms. The Gd(1)-Se(2) bond length is 3.09 Å. There are two shorter (3.08 Å) and two longer (3.22 Å) Gd(1)-Se(1) bond lengths. The Gd(1)-O(1) bond length is 2.27 Å. Both Gd(1)-O(2) bond lengths are 2.31 Å. In the second Gd site, Gd(2) is bonded in a 4-coordinate geometry to two equivalent Se(1), two equivalent Se(2), one O(2), and three equivalent O(1) atoms. Both Gd(2)-Se(1) bond lengths are 3.06 Å. Both Gd(2)-Se(2) bond lengths are 3.28 Å. The Gd(2)-O(2) bond length is 2.44 Å. There are two shorter (2.27 Å) and one longer (2.30 Å) Gd(2)-O(1) bond length. Ti(1) is bonded in a distorted linear geometry to four equivalent Se(2) and two equivalent O(2) atoms. All Ti(1)-Se(2) bond lengths are 2.66 Å. Both Ti(1)-O(2) bond lengths are 1.91 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Gd(2) and four equivalent Gd(1) atoms. In the second Se site, Se(2) is bonded in a distorted pentagonal planar geometry to one Gd(1), two equivalent Gd(2), and two equivalent Ti(1) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Gd(1) and three equivalent Gd(2) atoms to form OGd4 tetrahedra that share  a cornercorner with one O(2)Gd3Ti tetrahedra, corners with two equivalent O(1)Gd4 tetrahedra, edges with two equivalent O(2)Gd3Ti tetrahedra, and edges with two equivalent O(1)Gd4 tetrahedra. In the second O site, O(2) is bonded to one Gd(2), two equivalent Gd(1), and one Ti(1) atom to form distorted OGd3Ti tetrahedra that share  a cornercorner with one O(1)Gd4 tetrahedra, corners with three equivalent O(2)Gd3Ti tetrahedra, and edges with two equivalent O(1)Gd4 tetrahedra.