Y4TiSi2(O3F2)3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one O(2), one O(4), one F(3), and four equivalent F(1) atoms to form YO2F5 pentagonal bipyramids that share  a cornercorner with one Y(1)O2F5 pentagonal bipyramid, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Y(1)O2F5 pentagonal bipyramids. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), two equivalent O(1), one F(2), and two equivalent F(1) atoms. Ti(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra and corners with four equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. Si(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra and corners with two equivalent Y(1)O2F5 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(2), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Y(2), one Ti(1), and one Si(1) atom. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(2), and one Si(1) atom. In the fourth O site, O(3) is bonded to two equivalent Y(2) and two equivalent Ti(1) atoms to form distorted corner-sharing OY2Ti2 tetrahedra. There are three inequivalent F sites. In the first F site, F(1) is bonded in a trigonal planar geometry to one Y(2) and two equivalent Y(1) atoms. In the second F site, F(2) is bonded in a bent 120 degrees geometry to two equivalent Y(2) atoms. In the third F site, F(3) is bonded in a linear geometry to two equivalent Y(1) atoms.
Y4TiSi2(O3F2)3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one O(2), one O(4), one F(3), and four equivalent F(1) atoms to form YO2F5 pentagonal bipyramids that share  a cornercorner with one Y(1)O2F5 pentagonal bipyramid, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Y(1)O2F5 pentagonal bipyramids. The Y(1)-O(2) bond length is 2.29 Å. The Y(1)-O(4) bond length is 2.24 Å. The Y(1)-F(3) bond length is 2.21 Å. There are two shorter (2.28 Å) and two longer (2.32 Å) Y(1)-F(1) bond lengths. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), two equivalent O(1), one F(2), and two equivalent F(1) atoms. The Y(2)-O(2) bond length is 2.32 Å. The Y(2)-O(3) bond length is 2.50 Å. The Y(2)-O(4) bond length is 2.37 Å. Both Y(2)-O(1) bond lengths are 2.41 Å. The Y(2)-F(2) bond length is 2.21 Å. Both Y(2)-F(1) bond lengths are 2.36 Å. Ti(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra and corners with four equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. Both Ti(1)-O(3) bond lengths are 1.90 Å. All Ti(1)-O(1) bond lengths are 2.00 Å. Si(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra and corners with two equivalent Y(1)O2F5 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. The Si(1)-O(2) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.64 Å. Both Si(1)-O(1) bond lengths are 1.67 Å. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(2), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Y(2), one Ti(1), and one Si(1) atom. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(2), and one Si(1) atom. In the fourth O site, O(3) is bonded to two equivalent Y(2) and two equivalent Ti(1) atoms to form distorted corner-sharing OY2Ti2 tetrahedra. There are three inequivalent F sites. In the first F site, F(1) is bonded in a trigonal planar geometry to one Y(2) and two equivalent Y(1) atoms. In the second F site, F(2) is bonded in a bent 120 degrees geometry to two equivalent Y(2) atoms. In the third F site, F(3) is bonded in a linear geometry to two equivalent Y(1) atoms.