Na2Al2B2O7 crystallizes in the trigonal P-31c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted q6 geometry to three equivalent O(2) and six equivalent O(1) atoms. In the second Na site, Na(2) is bonded to six equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. B(1) is bonded in a trigonal planar geometry to three equivalent O(1) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Na(1), one Na(2), one Al(1), and one B(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to three equivalent Na(1) and two equivalent Al(1) atoms.
Na2Al2B2O7 crystallizes in the trigonal P-31c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted q6 geometry to three equivalent O(2) and six equivalent O(1) atoms. All Na(1)-O(2) bond lengths are 2.81 Å. All Na(1)-O(1) bond lengths are 2.92 Å. In the second Na site, Na(2) is bonded to six equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra. All Na(2)-O(1) bond lengths are 2.45 Å. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. The Al(1)-O(2) bond length is 1.73 Å. All Al(1)-O(1) bond lengths are 1.77 Å. B(1) is bonded in a trigonal planar geometry to three equivalent O(1) atoms. All B(1)-O(1) bond lengths are 1.38 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Na(1), one Na(2), one Al(1), and one B(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to three equivalent Na(1) and two equivalent Al(1) atoms.