Cs2BaP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 11-coordinate geometry to one O(1), one O(5), two equivalent O(3), two equivalent O(4), two equivalent O(7), and three equivalent O(6) atoms. In the second Cs site, Cs(2) is bonded in a 11-coordinate geometry to one O(3), one O(4), two equivalent O(1), two equivalent O(5), two equivalent O(7), and three equivalent O(2) atoms. Ba(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form BaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. 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 three equivalent Ba(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-39°. In the second P site, P(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ba(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 9-44°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Cs(2), two equivalent Cs(1), one P(1), and one P(2) atom. In the second O site, O(5) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Ba(1), and one P(1) atom. In the third O site, O(6) is bonded in a distorted single-bond geometry to three equivalent Cs(1), one Ba(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Cs(1), two equivalent Cs(2), one Ba(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Ba(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted single-bond geometry to three equivalent Cs(2), one Ba(1), and one P(1) atom. In the seventh O site, O(3) is bonded in a 1-coordinate geometry to one Cs(2), two equivalent Cs(1), one Ba(1), and one P(1) atom.
Cs2BaP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 11-coordinate geometry to one O(1), one O(5), two equivalent O(3), two equivalent O(4), two equivalent O(7), and three equivalent O(6) atoms. The Cs(1)-O(1) bond length is 3.16 Å. The Cs(1)-O(5) bond length is 3.36 Å. There is one shorter (3.28 Å) and one longer (3.61 Å) Cs(1)-O(3) bond length. There is one shorter (3.30 Å) and one longer (3.45 Å) Cs(1)-O(4) bond length. There is one shorter (3.35 Å) and one longer (3.76 Å) Cs(1)-O(7) bond length. There are a spread of Cs(1)-O(6) bond distances ranging from 3.19-3.71 Å. In the second Cs site, Cs(2) is bonded in a 11-coordinate geometry to one O(3), one O(4), two equivalent O(1), two equivalent O(5), two equivalent O(7), and three equivalent O(2) atoms. The Cs(2)-O(3) bond length is 3.13 Å. The Cs(2)-O(4) bond length is 3.55 Å. There is one shorter (3.21 Å) and one longer (3.32 Å) Cs(2)-O(1) bond length. There is one shorter (3.45 Å) and one longer (3.52 Å) Cs(2)-O(5) bond length. There is one shorter (3.29 Å) and one longer (3.73 Å) Cs(2)-O(7) bond length. There are a spread of Cs(2)-O(2) bond distances ranging from 3.14-3.42 Å. Ba(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form BaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. The Ba(1)-O(1) bond length is 2.77 Å. The Ba(1)-O(2) bond length is 2.69 Å. The Ba(1)-O(3) bond length is 2.68 Å. The Ba(1)-O(5) bond length is 2.68 Å. The Ba(1)-O(6) bond length is 2.67 Å. The Ba(1)-O(7) bond length is 2.67 Å. 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 three equivalent Ba(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-39°. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.65 Å. The P(1)-O(5) bond length is 1.53 Å. In the second P site, P(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ba(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 9-44°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(4) bond length is 1.66 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Cs(2), two equivalent Cs(1), one P(1), and one P(2) atom. In the second O site, O(5) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Ba(1), and one P(1) atom. In the third O site, O(6) is bonded in a distorted single-bond geometry to three equivalent Cs(1), one Ba(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Cs(1), two equivalent Cs(2), one Ba(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Ba(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted single-bond geometry to three equivalent Cs(2), one Ba(1), and one P(1) atom. In the seventh O site, O(3) is bonded in a 1-coordinate geometry to one Cs(2), two equivalent Cs(1), one Ba(1), and one P(1) atom.