Na2SrAl4(B2O7)2 crystallizes in the trigonal P3 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(5) atoms. In the second Na site, Na(2) is bonded to three equivalent O(3) and three equivalent O(5) atoms to form distorted NaO6 octahedra that share corners with three equivalent Al(2)O4 tetrahedra and corners with three equivalent Al(4)O4 tetrahedra. Sr(1) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form SrO6 octahedra that share corners with three equivalent Al(1)O4 tetrahedra and corners with three equivalent Al(3)O4 tetrahedra. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2) and three equivalent O(6) atoms to form AlO4 tetrahedra that share corners with three equivalent Sr(1)O6 octahedra and  a cornercorner with one Al(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. In the second Al site, Al(2) is bonded to one O(1) and three equivalent O(5) atoms to form AlO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one Al(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 69°. In the third Al site, Al(3) is bonded to one O(1) and three equivalent O(4) atoms to form AlO4 tetrahedra that share corners with three equivalent Sr(1)O6 octahedra and  a cornercorner with one Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 65°. In the fourth Al site, Al(4) is bonded to one O(2) and three equivalent O(3) 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 68°. There are four inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to three equivalent O(5) atoms. In the second B site, B(2) is bonded in a trigonal planar geometry to three equivalent O(6) atoms. In the third B site, B(3) is bonded in a trigonal planar geometry to three equivalent O(3) atoms. In the fourth B site, B(4) is bonded in a trigonal planar geometry to three equivalent O(4) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to three equivalent Na(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a linear geometry to one Al(1) and one Al(4) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(2), one Al(4), and one B(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sr(1), one Al(3), and one B(4) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Al(2), and one B(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(1), one Al(1), and one B(2) atom.
Na2SrAl4(B2O7)2 crystallizes in the trigonal P3 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(5) atoms. All Na(1)-O(1) bond lengths are 2.94 Å. All Na(1)-O(5) bond lengths are 2.42 Å. In the second Na site, Na(2) is bonded to three equivalent O(3) and three equivalent O(5) atoms to form distorted NaO6 octahedra that share corners with three equivalent Al(2)O4 tetrahedra and corners with three equivalent Al(4)O4 tetrahedra. All Na(2)-O(3) bond lengths are 2.31 Å. All Na(2)-O(5) bond lengths are 2.85 Å. Sr(1) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form SrO6 octahedra that share corners with three equivalent Al(1)O4 tetrahedra and corners with three equivalent Al(3)O4 tetrahedra. All Sr(1)-O(4) bond lengths are 2.65 Å. All Sr(1)-O(6) bond lengths are 2.52 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2) and three equivalent O(6) atoms to form AlO4 tetrahedra that share corners with three equivalent Sr(1)O6 octahedra and  a cornercorner with one Al(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. The Al(1)-O(2) bond length is 1.67 Å. All Al(1)-O(6) bond lengths are 1.80 Å. In the second Al site, Al(2) is bonded to one O(1) and three equivalent O(5) atoms to form AlO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one Al(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 69°. The Al(2)-O(1) bond length is 1.75 Å. All Al(2)-O(5) bond lengths are 1.77 Å. In the third Al site, Al(3) is bonded to one O(1) and three equivalent O(4) atoms to form AlO4 tetrahedra that share corners with three equivalent Sr(1)O6 octahedra and  a cornercorner with one Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 65°. The Al(3)-O(1) bond length is 1.71 Å. All Al(3)-O(4) bond lengths are 1.79 Å. In the fourth Al site, Al(4) is bonded to one O(2) and three equivalent O(3) 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 68°. The Al(4)-O(2) bond length is 1.73 Å. All Al(4)-O(3) bond lengths are 1.77 Å. There are four inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to three equivalent O(5) atoms. All B(1)-O(5) bond lengths are 1.39 Å. In the second B site, B(2) is bonded in a trigonal planar geometry to three equivalent O(6) atoms. All B(2)-O(6) bond lengths are 1.38 Å. In the third B site, B(3) is bonded in a trigonal planar geometry to three equivalent O(3) atoms. All B(3)-O(3) bond lengths are 1.38 Å. In the fourth B site, B(4) is bonded in a trigonal planar geometry to three equivalent O(4) atoms. All B(4)-O(4) bond lengths are 1.39 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to three equivalent Na(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a linear geometry to one Al(1) and one Al(4) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(2), one Al(4), and one B(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sr(1), one Al(3), and one B(4) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Al(2), and one B(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(1), one Al(1), and one B(2) atom.