Na7Al3O8 crystallizes in the triclinic P-1 space group. There are seven inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), one O(7), and one O(8) atom. In the second Na site, Na(2) is bonded to one O(3), one O(7), and two equivalent O(5) atoms to form distorted NaO4 trigonal pyramids that share  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent Al(2)O4 tetrahedra, corners with two equivalent Na(4)O4 trigonal pyramids,  an edgeedge with one Al(2)O4 tetrahedra,  an edgeedge with one Na(2)O4 trigonal pyramid, and  an edgeedge with one Na(4)O4 trigonal pyramid. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and one O(8) atom. In the fourth Na site, Na(4) is bonded to one O(5), one O(8), and two equivalent O(7) atoms to form NaO4 trigonal pyramids that share  a cornercorner with one Al(1)O4 tetrahedra, corners with three equivalent Al(2)O4 tetrahedra, corners with two equivalent Na(2)O4 trigonal pyramids,  an edgeedge with one Na(2)O4 trigonal pyramid, and  an edgeedge with one Na(4)O4 trigonal pyramid. In the fifth Na site, Na(5) is bonded in a 5-coordinate geometry to one O(2), one O(4), one O(5), one O(7), and one O(8) atom. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(4), and two equivalent O(2) atoms. In the seventh Na site, Na(7) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(1), and two equivalent O(6) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, and  a cornercorner with one Na(4)O4 trigonal pyramid. In the second Al site, Al(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent Na(2)O4 trigonal pyramids, corners with three equivalent Na(4)O4 trigonal pyramids, and  an edgeedge with one Na(2)O4 trigonal pyramid. In the third Al site, Al(3) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra, and  a cornercorner with one Na(2)O4 trigonal pyramid. There are eight inequivalent O sites. In the first O site, O(8) is bonded to one Na(1), one Na(3), one Na(4), one Na(5), one Na(7), and one Al(1) atom to form distorted corner-sharing ONa5Al octahedra. The corner-sharing octahedral tilt angles range from 47-59°. In the second O site, O(1) is bonded in a 3-coordinate geometry to one Na(6), two equivalent Na(7), one Al(1), and one Al(3) atom. In the third O site, O(2) is bonded to one Na(3), one Na(5), one Na(7), two equivalent Na(6), and one Al(3) atom to form a mixture of distorted corner and edge-sharing ONa5Al octahedra. The corner-sharing octahedral tilt angles range from 47-59°. In the fourth O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), one Al(2), and one Al(3) atom. In the fifth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Na(5), one Na(6), one Al(1), and one Al(2) atom. In the sixth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), one Na(4), one Na(5), two equivalent Na(2), and one Al(2) atom. In the seventh O site, O(6) is bonded in a 6-coordinate geometry to one Na(1), one Na(3), two equivalent Na(7), one Al(1), and one Al(3) atom. In the eighth O site, O(7) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(5), two equivalent Na(4), and one Al(2) atom.
Na7Al3O8 crystallizes in the triclinic P-1 space group. There are seven inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), one O(7), and one O(8) atom. The Na(1)-O(3) bond length is 2.88 Å. The Na(1)-O(4) bond length is 2.59 Å. The Na(1)-O(6) bond length is 2.27 Å. The Na(1)-O(7) bond length is 2.23 Å. The Na(1)-O(8) bond length is 2.27 Å. In the second Na site, Na(2) is bonded to one O(3), one O(7), and two equivalent O(5) atoms to form distorted NaO4 trigonal pyramids that share  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent Al(2)O4 tetrahedra, corners with two equivalent Na(4)O4 trigonal pyramids,  an edgeedge with one Al(2)O4 tetrahedra,  an edgeedge with one Na(2)O4 trigonal pyramid, and  an edgeedge with one Na(4)O4 trigonal pyramid. The Na(2)-O(3) bond length is 2.40 Å. The Na(2)-O(7) bond length is 2.31 Å. Both Na(2)-O(5) bond lengths are 2.29 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and one O(8) atom. The Na(3)-O(2) bond length is 2.36 Å. The Na(3)-O(3) bond length is 2.34 Å. The Na(3)-O(5) bond length is 2.52 Å. The Na(3)-O(6) bond length is 2.72 Å. The Na(3)-O(8) bond length is 2.36 Å. In the fourth Na site, Na(4) is bonded to one O(5), one O(8), and two equivalent O(7) atoms to form NaO4 trigonal pyramids that share  a cornercorner with one Al(1)O4 tetrahedra, corners with three equivalent Al(2)O4 tetrahedra, corners with two equivalent Na(2)O4 trigonal pyramids,  an edgeedge with one Na(2)O4 trigonal pyramid, and  an edgeedge with one Na(4)O4 trigonal pyramid. The Na(4)-O(5) bond length is 2.32 Å. The Na(4)-O(8) bond length is 2.36 Å. There is one shorter (2.25 Å) and one longer (2.32 Å) Na(4)-O(7) bond length. In the fifth Na site, Na(5) is bonded in a 5-coordinate geometry to one O(2), one O(4), one O(5), one O(7), and one O(8) atom. The Na(5)-O(2) bond length is 2.34 Å. The Na(5)-O(4) bond length is 2.69 Å. The Na(5)-O(5) bond length is 2.39 Å. The Na(5)-O(7) bond length is 2.64 Å. The Na(5)-O(8) bond length is 2.44 Å. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(4), and two equivalent O(2) atoms. The Na(6)-O(1) bond length is 2.31 Å. The Na(6)-O(4) bond length is 2.36 Å. There is one shorter (2.25 Å) and one longer (2.28 Å) Na(6)-O(2) bond length. In the seventh Na site, Na(7) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(1), and two equivalent O(6) atoms. The Na(7)-O(2) bond length is 2.42 Å. The Na(7)-O(8) bond length is 2.32 Å. There is one shorter (2.73 Å) and one longer (2.74 Å) Na(7)-O(1) bond length. There is one shorter (2.44 Å) and one longer (2.88 Å) Na(7)-O(6) bond length. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, and  a cornercorner with one Na(4)O4 trigonal pyramid. The Al(1)-O(1) bond length is 1.78 Å. The Al(1)-O(4) bond length is 1.78 Å. The Al(1)-O(6) bond length is 1.76 Å. The Al(1)-O(8) bond length is 1.74 Å. In the second Al site, Al(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent Na(2)O4 trigonal pyramids, corners with three equivalent Na(4)O4 trigonal pyramids, and  an edgeedge with one Na(2)O4 trigonal pyramid. The Al(2)-O(3) bond length is 1.80 Å. The Al(2)-O(4) bond length is 1.80 Å. The Al(2)-O(5) bond length is 1.75 Å. The Al(2)-O(7) bond length is 1.74 Å. In the third Al site, Al(3) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra, and  a cornercorner with one Na(2)O4 trigonal pyramid. The Al(3)-O(1) bond length is 1.78 Å. The Al(3)-O(2) bond length is 1.74 Å. The Al(3)-O(3) bond length is 1.76 Å. The Al(3)-O(6) bond length is 1.76 Å. There are eight inequivalent O sites. In the first O site, O(8) is bonded to one Na(1), one Na(3), one Na(4), one Na(5), one Na(7), and one Al(1) atom to form distorted corner-sharing ONa5Al octahedra. The corner-sharing octahedral tilt angles range from 47-59°. In the second O site, O(1) is bonded in a 3-coordinate geometry to one Na(6), two equivalent Na(7), one Al(1), and one Al(3) atom. In the third O site, O(2) is bonded to one Na(3), one Na(5), one Na(7), two equivalent Na(6), and one Al(3) atom to form a mixture of distorted corner and edge-sharing ONa5Al octahedra. The corner-sharing octahedral tilt angles range from 47-59°. In the fourth O site, O(3) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), one Al(2), and one Al(3) atom. In the fifth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Na(5), one Na(6), one Al(1), and one Al(2) atom. In the sixth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), one Na(4), one Na(5), two equivalent Na(2), and one Al(2) atom. In the seventh O site, O(6) is bonded in a 6-coordinate geometry to one Na(1), one Na(3), two equivalent Na(7), one Al(1), and one Al(3) atom. In the eighth O site, O(7) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(5), two equivalent Na(4), and one Al(2) atom.