Na2Nb4Se4O19 crystallizes in the triclinic P-1 space group. Na(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(6) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(8), and two equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 4-7°. In the second Nb site, Nb(2) is bonded to one O(3), one O(4), one O(8), one O(9), and two equivalent O(10) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-10°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Nb(1) and one Se(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Na(1), one Nb(1), and one Se(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(1), one Nb(2), and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(2) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(1) and one Se(2) atom. In the sixth O site, O(6) is bonded to three equivalent Na(1) and one Se(2) atom to form a mixture of distorted edge and corner-sharing ONa3Se tetrahedra. In the seventh O site, O(7) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the eighth O site, O(8) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent Nb(2) atoms. In the tenth O site, O(10) is bonded in a linear geometry to two equivalent Nb(2) atoms.
Na2Nb4Se4O19 crystallizes in the triclinic P-1 space group. Na(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(6) atoms. The Na(1)-O(3) bond length is 2.39 Å. There is one shorter (2.73 Å) and one longer (2.89 Å) Na(1)-O(2) bond length. There are a spread of Na(1)-O(6) bond distances ranging from 2.44-2.52 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(8), and two equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 4-7°. The Nb(1)-O(1) bond length is 2.06 Å. The Nb(1)-O(2) bond length is 2.16 Å. The Nb(1)-O(5) bond length is 2.00 Å. The Nb(1)-O(8) bond length is 1.93 Å. There is one shorter (1.83 Å) and one longer (2.19 Å) Nb(1)-O(7) bond length. In the second Nb site, Nb(2) is bonded to one O(3), one O(4), one O(8), one O(9), and two equivalent O(10) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-10°. The Nb(2)-O(3) bond length is 2.18 Å. The Nb(2)-O(4) bond length is 2.10 Å. The Nb(2)-O(8) bond length is 1.95 Å. The Nb(2)-O(9) bond length is 1.95 Å. There is one shorter (1.84 Å) and one longer (2.19 Å) Nb(2)-O(10) bond length. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. The Se(1)-O(1) bond length is 1.75 Å. The Se(1)-O(2) bond length is 1.73 Å. The Se(1)-O(3) bond length is 1.73 Å. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. The Se(2)-O(4) bond length is 1.75 Å. The Se(2)-O(5) bond length is 1.79 Å. The Se(2)-O(6) bond length is 1.68 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Nb(1) and one Se(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Na(1), one Nb(1), and one Se(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(1), one Nb(2), and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(2) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(1) and one Se(2) atom. In the sixth O site, O(6) is bonded to three equivalent Na(1) and one Se(2) atom to form a mixture of distorted edge and corner-sharing ONa3Se tetrahedra. In the seventh O site, O(7) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the eighth O site, O(8) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent Nb(2) atoms. In the tenth O site, O(10) is bonded in a linear geometry to two equivalent Nb(2) atoms.