Na2Sr2Nb4O13 crystallizes in the orthorhombic Imm2 space group. Na(1) is bonded to one O(2), one O(5), one O(7), two equivalent O(3), and two equivalent O(6) atoms to form distorted NaO7 hexagonal pyramids that share  a cornercorner with one Na(1)O7 hexagonal pyramid, corners with two equivalent Sr(1)O7 hexagonal pyramids,  an edgeedge with one Na(1)O7 hexagonal pyramid, edges with two equivalent Sr(1)O7 hexagonal pyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Nb(2)O6 octahedra. Sr(1) is bonded to one O(1), one O(4), one O(7), two equivalent O(3), and two equivalent O(6) atoms to form distorted SrO7 hexagonal pyramids that share  a cornercorner with one Sr(1)O7 hexagonal pyramid, corners with two equivalent Na(1)O7 hexagonal pyramids,  an edgeedge with one Sr(1)O7 hexagonal pyramid, edges with two equivalent Na(1)O7 hexagonal pyramids, edges with two equivalent Nb(2)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(4), two equivalent O(3), and two equivalent O(6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, edges with two equivalent Na(1)O7 hexagonal pyramids, and edges with four equivalent Sr(1)O7 hexagonal pyramids. The corner-sharing octahedral tilt angles range from 39-43°. In the second Nb site, Nb(2) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Sr(1)O7 hexagonal pyramids, and edges with four equivalent Na(1)O7 hexagonal pyramids. The corner-sharing octahedral tilt angles range from 36-42°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Na(1) and two equivalent Nb(2) atoms. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Sr(1), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded to two equivalent Sr(1) and two equivalent Nb(1) atoms to form distorted corner-sharing OSr2Nb2 tetrahedra. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Na(1) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Sr(1), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to two equivalent Na(1) and two equivalent Sr(1) atoms to form corner-sharing ONa2Sr2 tetrahedra.
Na2Sr2Nb4O13 crystallizes in the orthorhombic Imm2 space group. Na(1) is bonded to one O(2), one O(5), one O(7), two equivalent O(3), and two equivalent O(6) atoms to form distorted NaO7 hexagonal pyramids that share  a cornercorner with one Na(1)O7 hexagonal pyramid, corners with two equivalent Sr(1)O7 hexagonal pyramids,  an edgeedge with one Na(1)O7 hexagonal pyramid, edges with two equivalent Sr(1)O7 hexagonal pyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Nb(2)O6 octahedra. The Na(1)-O(2) bond length is 2.74 Å. The Na(1)-O(5) bond length is 2.77 Å. The Na(1)-O(7) bond length is 2.15 Å. Both Na(1)-O(3) bond lengths are 2.76 Å. Both Na(1)-O(6) bond lengths are 2.75 Å. Sr(1) is bonded to one O(1), one O(4), one O(7), two equivalent O(3), and two equivalent O(6) atoms to form distorted SrO7 hexagonal pyramids that share  a cornercorner with one Sr(1)O7 hexagonal pyramid, corners with two equivalent Na(1)O7 hexagonal pyramids,  an edgeedge with one Sr(1)O7 hexagonal pyramid, edges with two equivalent Na(1)O7 hexagonal pyramids, edges with two equivalent Nb(2)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. The Sr(1)-O(1) bond length is 2.74 Å. The Sr(1)-O(4) bond length is 2.69 Å. The Sr(1)-O(7) bond length is 2.18 Å. Both Sr(1)-O(3) bond lengths are 2.71 Å. Both Sr(1)-O(6) bond lengths are 2.73 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(4), two equivalent O(3), and two equivalent O(6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, edges with two equivalent Na(1)O7 hexagonal pyramids, and edges with four equivalent Sr(1)O7 hexagonal pyramids. The corner-sharing octahedral tilt angles range from 39-43°. The Nb(1)-O(1) bond length is 2.01 Å. The Nb(1)-O(4) bond length is 2.03 Å. Both Nb(1)-O(3) bond lengths are 2.00 Å. Both Nb(1)-O(6) bond lengths are 2.02 Å. In the second Nb site, Nb(2) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Sr(1)O7 hexagonal pyramids, and edges with four equivalent Na(1)O7 hexagonal pyramids. The corner-sharing octahedral tilt angles range from 36-42°. The Nb(2)-O(2) bond length is 2.00 Å. The Nb(2)-O(5) bond length is 2.02 Å. Both Nb(2)-O(3) bond lengths are 2.02 Å. Both Nb(2)-O(6) bond lengths are 2.02 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Na(1) and two equivalent Nb(2) atoms. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Sr(1), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded to two equivalent Sr(1) and two equivalent Nb(1) atoms to form distorted corner-sharing OSr2Nb2 tetrahedra. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Na(1) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Sr(1), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to two equivalent Na(1) and two equivalent Sr(1) atoms to form corner-sharing ONa2Sr2 tetrahedra.