Ca2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), two equivalent O(6), and two equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form corner-sharing PO4 tetrahedra. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing PO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(6) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one P(2) atom. In the third O site, O(7) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one P(2) atom. In the fourth O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one P(1) atom. In the fifth O site, O(2) is bonded in a 1-coordinate geometry to one Ca(1), two equivalent Ca(2), and one P(1) atom. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one P(1) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one P(2) atom.
Ca2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), two equivalent O(6), and two equivalent O(7) atoms. The Ca(1)-O(1) bond length is 2.25 Å. The Ca(1)-O(2) bond length is 2.50 Å. The Ca(1)-O(3) bond length is 2.55 Å. The Ca(1)-O(4) bond length is 2.43 Å. There is one shorter (2.39 Å) and one longer (2.69 Å) Ca(1)-O(6) bond length. There is one shorter (2.48 Å) and one longer (2.61 Å) Ca(1)-O(7) bond length. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms. The Ca(2)-O(1) bond length is 2.48 Å. The Ca(2)-O(4) bond length is 2.36 Å. The Ca(2)-O(6) bond length is 2.72 Å. The Ca(2)-O(7) bond length is 2.39 Å. There is one shorter (2.33 Å) and one longer (2.80 Å) Ca(2)-O(2) bond length. There is one shorter (2.43 Å) and one longer (2.78 Å) Ca(2)-O(3) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form corner-sharing PO4 tetrahedra. The P(1)-O(1) bond length is 1.50 Å. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.60 Å. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing PO4 tetrahedra. The P(2)-O(4) bond length is 1.50 Å. The P(2)-O(5) bond length is 1.59 Å. The P(2)-O(6) bond length is 1.52 Å. The P(2)-O(7) bond length is 1.54 Å. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(6) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one P(2) atom. In the third O site, O(7) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one P(2) atom. In the fourth O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one P(1) atom. In the fifth O site, O(2) is bonded in a 1-coordinate geometry to one Ca(1), two equivalent Ca(2), and one P(1) atom. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one P(1) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one P(2) atom.