Na2CaP2O11 crystallizes in the monoclinic Pc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(10), one O(11), one O(2), one O(6), one O(7), one O(8), and one O(9) atom. In the second Na site, Na(2) is bonded to one O(10), one O(4), one O(5), one O(6), and one O(9) atom to form distorted NaO5 square pyramids that share  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 octahedra. Ca(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form CaO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Na(2)O5 square pyramid. 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(4) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra,  a cornercorner with one Na(2)O5 square pyramid, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-60°. In the second P site, P(2) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Na(2)O5 square pyramids, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-56°. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Ca(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one P(1), and one P(2) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Ca(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(2), one Ca(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Na(2), one Ca(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one Ca(1), and one P(2) atom. In the eighth O site, O(8) is bonded in an L-shaped geometry to one Na(1) and one Ca(1) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Na(1), one Na(2), and one O(11) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Na(1) and one Na(2) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Na(1) and one O(9) atom.
Na2CaP2O11 crystallizes in the monoclinic Pc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(10), one O(11), one O(2), one O(6), one O(7), one O(8), and one O(9) atom. The Na(1)-O(10) bond length is 2.53 Å. The Na(1)-O(11) bond length is 2.62 Å. The Na(1)-O(2) bond length is 2.50 Å. The Na(1)-O(6) bond length is 2.39 Å. The Na(1)-O(7) bond length is 2.37 Å. The Na(1)-O(8) bond length is 2.34 Å. The Na(1)-O(9) bond length is 2.84 Å. In the second Na site, Na(2) is bonded to one O(10), one O(4), one O(5), one O(6), and one O(9) atom to form distorted NaO5 square pyramids that share  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 octahedra. The Na(2)-O(10) bond length is 2.49 Å. The Na(2)-O(4) bond length is 2.29 Å. The Na(2)-O(5) bond length is 2.42 Å. The Na(2)-O(6) bond length is 2.28 Å. The Na(2)-O(9) bond length is 2.80 Å. Ca(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form CaO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Na(2)O5 square pyramid. The Ca(1)-O(1) bond length is 2.39 Å. The Ca(1)-O(3) bond length is 2.36 Å. The Ca(1)-O(4) bond length is 2.29 Å. The Ca(1)-O(5) bond length is 2.39 Å. The Ca(1)-O(7) bond length is 2.38 Å. The Ca(1)-O(8) bond length is 2.41 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(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra,  a cornercorner with one Na(2)O5 square pyramid, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-60°. The P(1)-O(1) bond length is 1.53 Å. The P(1)-O(2) bond length is 1.66 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Na(2)O5 square pyramids, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-56°. The P(2)-O(2) bond length is 1.65 Å. The P(2)-O(5) bond length is 1.53 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.54 Å. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Ca(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one P(1), and one P(2) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Ca(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(2), one Ca(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Na(2), one Ca(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one Ca(1), and one P(2) atom. In the eighth O site, O(8) is bonded in an L-shaped geometry to one Na(1) and one Ca(1) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Na(1), one Na(2), and one O(11) atom. The O(9)-O(11) bond length is 1.24 Å. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Na(1) and one Na(2) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Na(1) and one O(9) atom.