Cd2Si(P2O7)2 crystallizes in the monoclinic C2/c space group. Cd(1) is bonded to one O(4), one O(7), two equivalent O(5), and two equivalent O(6) atoms to form CdO6 octahedra that share corners with two equivalent Cd(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Cd(1)O6 octahedra. The corner-sharing octahedral tilt angles are 66°. Si(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form SiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with two equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Cd(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 44-56°. In the second P site, P(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Cd(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-59°. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Si(1) and one P(2) atom. In the third O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cd(1) and one P(1) atom. In the fourth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Cd(1) and one P(1) atom. In the fifth O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Cd(1) and one P(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Cd(1) and one P(2) atom. In the seventh O site, O(1) is bonded in a linear geometry to one Si(1) and one P(1) atom.
Cd2Si(P2O7)2 crystallizes in the monoclinic C2/c space group. Cd(1) is bonded to one O(4), one O(7), two equivalent O(5), and two equivalent O(6) atoms to form CdO6 octahedra that share corners with two equivalent Cd(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Cd(1)O6 octahedra. The corner-sharing octahedral tilt angles are 66°. The Cd(1)-O(4) bond length is 2.24 Å. The Cd(1)-O(7) bond length is 2.24 Å. There is one shorter (2.37 Å) and one longer (2.38 Å) Cd(1)-O(5) bond length. There is one shorter (2.36 Å) and one longer (2.37 Å) Cd(1)-O(6) bond length. Si(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form SiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with two equivalent P(2)O4 tetrahedra. Both Si(1)-O(1) bond lengths are 1.62 Å. Both Si(1)-O(3) bond lengths are 1.63 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Cd(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 44-56°. The P(1)-O(1) bond length is 1.57 Å. The P(1)-O(2) bond length is 1.62 Å. The P(1)-O(4) bond length is 1.50 Å. The P(1)-O(5) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Cd(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-59°. The P(2)-O(2) bond length is 1.62 Å. The P(2)-O(3) bond length is 1.58 Å. The P(2)-O(6) bond length is 1.53 Å. The P(2)-O(7) bond length is 1.50 Å. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Si(1) and one P(2) atom. In the third O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cd(1) and one P(1) atom. In the fourth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Cd(1) and one P(1) atom. In the fifth O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Cd(1) and one P(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Cd(1) and one P(2) atom. In the seventh O site, O(1) is bonded in a linear geometry to one Si(1) and one P(1) atom.