Sr2TiP2O9 crystallizes in the monoclinic Cc space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 11-coordinate geometry to one O(1), one O(2), one O(3), two equivalent O(4), two equivalent O(5), two equivalent O(8), and two equivalent O(9) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. Ti(1) is bonded to one O(2), one O(3), one O(6), one O(7), and two equivalent O(1) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-51°. In the second P site, P(2) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form PO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-44°. There are nine inequivalent O sites. In the first O site, O(8) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(2) atom. In the second O site, O(9) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(2) atom. In the third O site, O(1) is bonded in a 3-coordinate geometry to one Sr(1) and two equivalent Ti(1) atoms. In the fourth O site, O(2) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Ti(1), and one P(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Ti(1), and one P(1) atom. In the sixth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(1) atom. In the seventh O site, O(5) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(1) atom. In the eighth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(2), one Ti(1), and one P(2) atom. In the ninth O site, O(7) is bonded in a 3-coordinate geometry to one Sr(2), one Ti(1), and one P(2) atom.
Sr2TiP2O9 crystallizes in the monoclinic Cc space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 11-coordinate geometry to one O(1), one O(2), one O(3), two equivalent O(4), two equivalent O(5), two equivalent O(8), and two equivalent O(9) atoms. The Sr(1)-O(1) bond length is 2.62 Å. The Sr(1)-O(2) bond length is 2.91 Å. The Sr(1)-O(3) bond length is 2.91 Å. There is one shorter (2.68 Å) and one longer (3.12 Å) Sr(1)-O(4) bond length. There is one shorter (2.68 Å) and one longer (3.13 Å) Sr(1)-O(5) bond length. There is one shorter (2.70 Å) and one longer (2.71 Å) Sr(1)-O(8) bond length. There is one shorter (2.70 Å) and one longer (2.72 Å) Sr(1)-O(9) bond length. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Sr(2)-O(2) bond length is 2.54 Å. The Sr(2)-O(3) bond length is 2.54 Å. The Sr(2)-O(4) bond length is 2.68 Å. The Sr(2)-O(5) bond length is 2.68 Å. The Sr(2)-O(6) bond length is 2.75 Å. The Sr(2)-O(7) bond length is 2.75 Å. The Sr(2)-O(8) bond length is 2.56 Å. The Sr(2)-O(9) bond length is 2.57 Å. Ti(1) is bonded to one O(2), one O(3), one O(6), one O(7), and two equivalent O(1) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. The Ti(1)-O(2) bond length is 2.02 Å. The Ti(1)-O(3) bond length is 2.03 Å. The Ti(1)-O(6) bond length is 2.05 Å. The Ti(1)-O(7) bond length is 2.05 Å. There is one shorter (1.75 Å) and one longer (2.07 Å) Ti(1)-O(1) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-51°. The P(1)-O(2) bond length is 1.58 Å. The P(1)-O(3) bond length is 1.58 Å. The P(1)-O(4) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.53 Å. In the second P site, P(2) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form PO4 tetrahedra that share corners with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-44°. The P(2)-O(6) bond length is 1.57 Å. The P(2)-O(7) bond length is 1.58 Å. The P(2)-O(8) bond length is 1.54 Å. The P(2)-O(9) bond length is 1.54 Å. There are nine inequivalent O sites. In the first O site, O(8) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(2) atom. In the second O site, O(9) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(2) atom. In the third O site, O(1) is bonded in a 3-coordinate geometry to one Sr(1) and two equivalent Ti(1) atoms. In the fourth O site, O(2) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Ti(1), and one P(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Ti(1), and one P(1) atom. In the sixth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(1) atom. In the seventh O site, O(5) is bonded in a distorted single-bond geometry to one Sr(2), two equivalent Sr(1), and one P(1) atom. In the eighth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(2), one Ti(1), and one P(2) atom. In the ninth O site, O(7) is bonded in a 3-coordinate geometry to one Sr(2), one Ti(1), and one P(2) atom.