Na4Cr2P4O15 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom. In the second Na site, Na(2) is bonded to one O(1), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form distorted NaO6 pentagonal pyramids that share  a cornercorner with one Na(2)O6 pentagonal pyramid,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one Na(2)O6 pentagonal pyramid, and  an edgeedge with one P(1)O4 tetrahedra. Cr(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. 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  a cornercorner with one Na(2)O6 pentagonal pyramid,  a cornercorner with one P(2)O4 tetrahedra, and  an edgeedge with one Na(2)O6 pentagonal pyramid. 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 Na(2)O6 pentagonal pyramids and  a cornercorner with one P(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(1) atom. In the second O site, O(5) is bonded in a distorted trigonal planar geometry to one Na(1), one Cr(1), and one P(2) atom. In the third O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Cr(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Na(2), one Cr(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a distorted linear geometry to two equivalent Na(2) atoms. In the sixth O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Cr(1), and one P(1) atom. In the seventh 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 eighth O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Cr(1), and one P(1) atom.
Na4Cr2P4O15 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom. The Na(1)-O(1) bond length is 2.46 Å. The Na(1)-O(2) bond length is 2.51 Å. The Na(1)-O(3) bond length is 2.37 Å. The Na(1)-O(4) bond length is 2.35 Å. The Na(1)-O(5) bond length is 2.27 Å. The Na(1)-O(6) bond length is 2.47 Å. In the second Na site, Na(2) is bonded to one O(1), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form distorted NaO6 pentagonal pyramids that share  a cornercorner with one Na(2)O6 pentagonal pyramid,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one Na(2)O6 pentagonal pyramid, and  an edgeedge with one P(1)O4 tetrahedra. The Na(2)-O(1) bond length is 2.46 Å. The Na(2)-O(3) bond length is 2.68 Å. The Na(2)-O(4) bond length is 2.33 Å. The Na(2)-O(8) bond length is 2.66 Å. There is one shorter (2.34 Å) and one longer (2.87 Å) Na(2)-O(7) bond length. Cr(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. The Cr(1)-O(1) bond length is 2.02 Å. The Cr(1)-O(3) bond length is 2.06 Å. The Cr(1)-O(5) bond length is 2.03 Å. The Cr(1)-O(6) bond length is 2.02 Å. The Cr(1)-O(7) bond length is 2.73 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  a cornercorner with one Na(2)O6 pentagonal pyramid,  a cornercorner with one P(2)O4 tetrahedra, and  an edgeedge with one Na(2)O6 pentagonal pyramid. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(2) bond length is 1.64 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.50 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 Na(2)O6 pentagonal pyramids and  a cornercorner with one P(1)O4 tetrahedra. The P(2)-O(2) bond length is 1.64 Å. The P(2)-O(5) bond length is 1.55 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.51 Å. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(1) atom. In the second O site, O(5) is bonded in a distorted trigonal planar geometry to one Na(1), one Cr(1), and one P(2) atom. In the third O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Cr(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Na(2), one Cr(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a distorted linear geometry to two equivalent Na(2) atoms. In the sixth O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Cr(1), and one P(1) atom. In the seventh 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 eighth O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Cr(1), and one P(1) atom.