Na2V6O15 crystallizes in the monoclinic Cm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(12), one O(14), one O(3), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(12), one O(3), and two equivalent O(11) atoms. There are six inequivalent V sites. In the first V site, V(1) is bonded in a 6-coordinate geometry to one O(1), one O(13), one O(5), one O(6), and two equivalent O(2) atoms. In the second V site, V(2) is bonded in a 6-coordinate geometry to one O(10), one O(15), one O(2), one O(4), and two equivalent O(6) atoms. In the third V site, V(3) is bonded to one O(3), one O(5), one O(8), and two equivalent O(7) atoms to form distorted VO5 trigonal bipyramids that share  a cornercorner with one V(5)O6 octahedra, corners with two equivalent V(3)O5 trigonal bipyramids, and edges with two equivalent V(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. In the fourth V site, V(4) is bonded to one O(10), one O(12), one O(7), and two equivalent O(8) atoms to form a mixture of distorted edge and corner-sharing VO5 trigonal bipyramids. In the fifth V site, V(5) is bonded to one O(11), one O(13), one O(15), one O(5), and two equivalent O(9) atoms to form distorted VO6 octahedra that share corners with two equivalent V(5)O6 octahedra and  a cornercorner with one V(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 30°. In the sixth V site, V(6) is bonded in a 6-coordinate geometry to one O(10), one O(14), one O(2), one O(9), and two equivalent O(13) atoms. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one Na(2) and one V(1) atom. In the second O site, O(2) is bonded to one V(2), one V(6), and two equivalent V(1) atoms to form a mixture of distorted edge and corner-sharing OV4 trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one V(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Na(1) and one V(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one V(1), one V(3), and one V(5) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one V(1) and two equivalent V(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one V(4) and two equivalent V(3) atoms. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one V(3) and two equivalent V(4) atoms. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one V(6) and two equivalent V(5) atoms. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one V(2), one V(4), and one V(6) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to two equivalent Na(2) and one V(5) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one V(4) atom. In the thirteenth O site, O(13) is bonded to one V(1), one V(5), and two equivalent V(6) atoms to form a mixture of distorted edge and corner-sharing OV4 trigonal pyramids. In the fourteenth O site, O(14) is bonded in a linear geometry to one Na(1) and one V(6) atom. In the fifteenth O site, O(15) is bonded in a linear geometry to one V(2) and one V(5) atom.
Na2V6O15 crystallizes in the monoclinic Cm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(12), one O(14), one O(3), and two equivalent O(4) atoms. The Na(1)-O(12) bond length is 2.80 Å. The Na(1)-O(14) bond length is 2.19 Å. The Na(1)-O(3) bond length is 2.24 Å. Both Na(1)-O(4) bond lengths are 2.32 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(12), one O(3), and two equivalent O(11) atoms. The Na(2)-O(1) bond length is 2.22 Å. The Na(2)-O(12) bond length is 2.27 Å. The Na(2)-O(3) bond length is 2.80 Å. Both Na(2)-O(11) bond lengths are 2.31 Å. There are six inequivalent V sites. In the first V site, V(1) is bonded in a 6-coordinate geometry to one O(1), one O(13), one O(5), one O(6), and two equivalent O(2) atoms. The V(1)-O(1) bond length is 1.62 Å. The V(1)-O(13) bond length is 2.32 Å. The V(1)-O(5) bond length is 1.82 Å. The V(1)-O(6) bond length is 2.06 Å. Both V(1)-O(2) bond lengths are 1.92 Å. In the second V site, V(2) is bonded in a 6-coordinate geometry to one O(10), one O(15), one O(2), one O(4), and two equivalent O(6) atoms. The V(2)-O(10) bond length is 2.49 Å. The V(2)-O(15) bond length is 1.72 Å. The V(2)-O(2) bond length is 2.20 Å. The V(2)-O(4) bond length is 1.67 Å. Both V(2)-O(6) bond lengths are 1.92 Å. In the third V site, V(3) is bonded to one O(3), one O(5), one O(8), and two equivalent O(7) atoms to form distorted VO5 trigonal bipyramids that share  a cornercorner with one V(5)O6 octahedra, corners with two equivalent V(3)O5 trigonal bipyramids, and edges with two equivalent V(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. The V(3)-O(3) bond length is 1.66 Å. The V(3)-O(5) bond length is 2.04 Å. The V(3)-O(8) bond length is 2.06 Å. Both V(3)-O(7) bond lengths are 1.96 Å. In the fourth V site, V(4) is bonded to one O(10), one O(12), one O(7), and two equivalent O(8) atoms to form a mixture of distorted edge and corner-sharing VO5 trigonal bipyramids. The V(4)-O(10) bond length is 1.92 Å. The V(4)-O(12) bond length is 1.65 Å. The V(4)-O(7) bond length is 1.98 Å. Both V(4)-O(8) bond lengths are 1.93 Å. In the fifth V site, V(5) is bonded to one O(11), one O(13), one O(15), one O(5), and two equivalent O(9) atoms to form distorted VO6 octahedra that share corners with two equivalent V(5)O6 octahedra and  a cornercorner with one V(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 30°. The V(5)-O(11) bond length is 1.66 Å. The V(5)-O(13) bond length is 2.21 Å. The V(5)-O(15) bond length is 1.98 Å. The V(5)-O(5) bond length is 2.15 Å. Both V(5)-O(9) bond lengths are 1.90 Å. In the sixth V site, V(6) is bonded in a 6-coordinate geometry to one O(10), one O(14), one O(2), one O(9), and two equivalent O(13) atoms. The V(6)-O(10) bond length is 1.80 Å. The V(6)-O(14) bond length is 1.62 Å. The V(6)-O(2) bond length is 2.35 Å. The V(6)-O(9) bond length is 2.11 Å. Both V(6)-O(13) bond lengths are 1.92 Å. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one Na(2) and one V(1) atom. In the second O site, O(2) is bonded to one V(2), one V(6), and two equivalent V(1) atoms to form a mixture of distorted edge and corner-sharing OV4 trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one V(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Na(1) and one V(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one V(1), one V(3), and one V(5) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one V(1) and two equivalent V(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one V(4) and two equivalent V(3) atoms. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one V(3) and two equivalent V(4) atoms. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one V(6) and two equivalent V(5) atoms. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one V(2), one V(4), and one V(6) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to two equivalent Na(2) and one V(5) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one V(4) atom. In the thirteenth O site, O(13) is bonded to one V(1), one V(5), and two equivalent V(6) atoms to form a mixture of distorted edge and corner-sharing OV4 trigonal pyramids. In the fourteenth O site, O(14) is bonded in a linear geometry to one Na(1) and one V(6) atom. In the fifteenth O site, O(15) is bonded in a linear geometry to one V(2) and one V(5) atom.