Ba2TiSi2O8 crystallizes in the tetragonal P4bm space group. Ba(1) is bonded in a 10-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(4), and four equivalent O(2) atoms. Ti(1) is bonded to one O(1) and four equivalent O(2) atoms to form distorted TiO5 trigonal bipyramids that share corners with four equivalent Si(1)O4 tetrahedra. Si(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Ti(1)O5 trigonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to four equivalent Ba(1) and one Ti(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1) and two equivalent Si(1) atoms. In the fourth O site, O(4) is bonded to three equivalent Ba(1) and one Si(1) atom to form a mixture of distorted corner and edge-sharing OBa3Si tetrahedra.
Ba2TiSi2O8 crystallizes in the tetragonal P4bm space group. Ba(1) is bonded in a 10-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(4), and four equivalent O(2) atoms. The Ba(1)-O(3) bond length is 2.85 Å. Both Ba(1)-O(1) bond lengths are 3.36 Å. There is one shorter (2.67 Å) and two longer (2.82 Å) Ba(1)-O(4) bond lengths. There are two shorter (2.85 Å) and two longer (3.01 Å) Ba(1)-O(2) bond lengths. Ti(1) is bonded to one O(1) and four equivalent O(2) atoms to form distorted TiO5 trigonal bipyramids that share corners with four equivalent Si(1)O4 tetrahedra. The Ti(1)-O(1) bond length is 1.70 Å. All Ti(1)-O(2) bond lengths are 1.97 Å. Si(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Ti(1)O5 trigonal bipyramids. The Si(1)-O(3) bond length is 1.66 Å. The Si(1)-O(4) bond length is 1.59 Å. Both Si(1)-O(2) bond lengths are 1.63 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to four equivalent Ba(1) and one Ti(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1) and two equivalent Si(1) atoms. In the fourth O site, O(4) is bonded to three equivalent Ba(1) and one Si(1) atom to form a mixture of distorted corner and edge-sharing OBa3Si tetrahedra.