Na2NbAsO6 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(6) and four equivalent O(3) atoms. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with three equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. As(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-50°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(3), and one Nb(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(3), one Nb(1), and one As(1) atom. In the third O site, O(3) is bonded to one Na(1), two equivalent Na(2), and one As(1) atom to form distorted ONa3As trigonal pyramids that share corners with two equivalent O(6)Na2NbAs trigonal pyramids, corners with four equivalent O(3)Na3As trigonal pyramids,  an edgeedge with one O(3)Na3As trigonal pyramid, and edges with two equivalent O(6)Na2NbAs trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Nb(1), and one As(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Na(2), one Nb(1), and one As(1) atom to form distorted ONa2NbAs trigonal pyramids that share  a cornercorner with one O(6)Na2NbAs trigonal pyramid, corners with two equivalent O(3)Na3As trigonal pyramids, and edges with two equivalent O(3)Na3As trigonal pyramids.
Na2NbAsO6 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms. The Na(1)-O(1) bond length is 2.37 Å. The Na(1)-O(3) bond length is 2.34 Å. The Na(1)-O(4) bond length is 2.45 Å. The Na(1)-O(6) bond length is 2.45 Å. There is one shorter (2.63 Å) and one longer (2.68 Å) Na(1)-O(5) bond length. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(6) and four equivalent O(3) atoms. Both Na(2)-O(6) bond lengths are 2.57 Å. There are two shorter (2.39 Å) and two longer (2.51 Å) Na(2)-O(3) bond lengths. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both Na(3)-O(2) bond lengths are 2.57 Å. There are two shorter (2.37 Å) and two longer (2.71 Å) Na(3)-O(1) bond lengths. Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with three equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. The Nb(1)-O(1) bond length is 1.81 Å. The Nb(1)-O(2) bond length is 2.07 Å. The Nb(1)-O(5) bond length is 2.16 Å. The Nb(1)-O(6) bond length is 2.26 Å. There is one shorter (1.92 Å) and one longer (2.04 Å) Nb(1)-O(4) bond length. As(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-50°. The As(1)-O(2) bond length is 1.74 Å. The As(1)-O(3) bond length is 1.69 Å. The As(1)-O(5) bond length is 1.75 Å. The As(1)-O(6) bond length is 1.73 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(3), and one Nb(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(3), one Nb(1), and one As(1) atom. In the third O site, O(3) is bonded to one Na(1), two equivalent Na(2), and one As(1) atom to form distorted ONa3As trigonal pyramids that share corners with two equivalent O(6)Na2NbAs trigonal pyramids, corners with four equivalent O(3)Na3As trigonal pyramids,  an edgeedge with one O(3)Na3As trigonal pyramid, and edges with two equivalent O(6)Na2NbAs trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Nb(1), and one As(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Na(2), one Nb(1), and one As(1) atom to form distorted ONa2NbAs trigonal pyramids that share  a cornercorner with one O(6)Na2NbAs trigonal pyramid, corners with two equivalent O(3)Na3As trigonal pyramids, and edges with two equivalent O(3)Na3As trigonal pyramids.