Na2BaSi2O6 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(5), and two equivalent O(1) atoms. Ba(1) is bonded in a 8-coordinate geometry to one O(1), one O(6), three equivalent O(4), and three equivalent O(5) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Si(2)O4 tetrahedra and  a cornercorner with one Na(1)O5 trigonal bipyramid. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ba(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Na(2), three equivalent Ba(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(2), three equivalent Ba(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom.
Na2BaSi2O6 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The Na(1)-O(1) bond length is 2.30 Å. The Na(1)-O(2) bond length is 2.35 Å. There are a spread of Na(1)-O(3) bond distances ranging from 2.35-2.57 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(5), and two equivalent O(1) atoms. The Na(2)-O(2) bond length is 2.72 Å. The Na(2)-O(3) bond length is 2.38 Å. The Na(2)-O(4) bond length is 2.82 Å. The Na(2)-O(5) bond length is 2.79 Å. There is one shorter (2.49 Å) and one longer (2.50 Å) Na(2)-O(1) bond length. Ba(1) is bonded in a 8-coordinate geometry to one O(1), one O(6), three equivalent O(4), and three equivalent O(5) atoms. The Ba(1)-O(1) bond length is 2.73 Å. The Ba(1)-O(6) bond length is 3.10 Å. There are a spread of Ba(1)-O(4) bond distances ranging from 2.77-3.04 Å. There are a spread of Ba(1)-O(5) bond distances ranging from 2.75-2.94 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Si(2)O4 tetrahedra and  a cornercorner with one Na(1)O5 trigonal bipyramid. The Si(1)-O(2) bond length is 1.68 Å. The Si(1)-O(4) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.62 Å. The Si(1)-O(6) bond length is 1.68 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(2) bond length is 1.69 Å. The Si(2)-O(3) bond length is 1.61 Å. The Si(2)-O(6) bond length is 1.68 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ba(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Na(2), three equivalent Ba(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(2), three equivalent Ba(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom.