NaTa4O8 crystallizes in the monoclinic Cm space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(10), two equivalent O(4), and two equivalent O(8) atoms. In the second Na site, Na(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(11), two equivalent O(3), and two equivalent O(5) atoms. In the third Na site, Na(3) is bonded in a 8-coordinate geometry to two equivalent O(12), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. There are eight inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a distorted square co-planar geometry to two equivalent O(12) and two equivalent O(5) atoms. In the second Ta site, Ta(2) is bonded in a distorted square co-planar geometry to two equivalent O(11) and two equivalent O(6) atoms. In the third Ta site, Ta(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(10) and two equivalent O(7) atoms. In the fourth Ta site, Ta(4) is bonded in a distorted square co-planar geometry to two equivalent O(8) and two equivalent O(9) atoms. In the fifth Ta site, Ta(5) is bonded to one O(11), one O(2), one O(3), one O(6), one O(7), and one O(9) atom to form a mixture of corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 58°. In the sixth Ta site, Ta(6) is bonded to one O(1), one O(10), one O(12), one O(4), one O(5), and one O(8) atom to form a mixture of distorted corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 33°. In the seventh Ta site, Ta(7) is bonded to one O(12), one O(2), one O(4), one O(6), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing TaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 30-70°. In the eighth Ta site, Ta(8) is bonded to one O(1), one O(10), one O(11), one O(3), one O(5), and one O(7) atom to form a mixture of corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 33-58°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Ta(6), and one Ta(8) atom to form distorted ONa2Ta2 trigonal pyramids that share corners with three equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(12)NaTa3 trigonal pyramid,  a cornercorner with one O(8)NaTa3 trigonal pyramid, corners with two equivalent O(10)NaTa3 trigonal pyramids,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid,  an edgeedge with one O(10)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Na(3), one Ta(5), and one Ta(7) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(2), one Ta(5), and one Ta(8) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ta(6), and one Ta(7) atom to form ONa2Ta2 tetrahedra that share  a cornercorner with one O(10)NaTa3 trigonal pyramid,  a cornercorner with one O(6)NaTa3 trigonal pyramid, corners with two equivalent O(12)NaTa3 trigonal pyramids, corners with two equivalent O(8)NaTa3 trigonal pyramids, corners with three equivalent O(1)Na2Ta2 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(10)NaTa3 trigonal pyramid,  an edgeedge with one O(12)NaTa3 trigonal pyramid,  an edgeedge with one O(6)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(2), one Ta(1), one Ta(6), and one Ta(8) atom. In the sixth O site, O(6) is bonded to one Na(3), one Ta(2), one Ta(5), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share  a cornercorner with one O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(8)NaTa3 trigonal pyramid, corners with three equivalent O(12)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra, and  an edgeedge with one O(6)NaTa3 trigonal pyramid. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Ta(3), one Ta(5), and one Ta(8) atom. In the eighth O site, O(8) is bonded to one Na(1), one Ta(4), one Ta(6), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share corners with two equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(1)Na2Ta2 trigonal pyramid,  a cornercorner with one O(6)NaTa3 trigonal pyramid, corners with three equivalent O(10)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid,  an edgeedge with one O(12)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Ta(4), one Ta(5), and one Ta(7) atom. In the tenth O site, O(10) is bonded to one Na(1), one Ta(3), one Ta(6), and one Ta(8) atom to form distorted ONaTa3 trigonal pyramids that share  a cornercorner with one O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(12)NaTa3 trigonal pyramid, corners with two equivalent O(1)Na2Ta2 trigonal pyramids, corners with three equivalent O(8)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid, and  an edgeedge with one O(10)NaTa3 trigonal pyramid. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Na(2), one Ta(2), one Ta(5), and one Ta(8) atom. In the twelfth O site, O(12) is bonded to one Na(3), one Ta(1), one Ta(6), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share corners with two equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(1)Na2Ta2 trigonal pyramid,  a cornercorner with one O(10)NaTa3 trigonal pyramid, corners with three equivalent O(6)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(12)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid.
NaTa4O8 crystallizes in the monoclinic Cm space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(10), two equivalent O(4), and two equivalent O(8) atoms. Both Na(1)-O(1) bond lengths are 2.42 Å. Both Na(1)-O(10) bond lengths are 2.64 Å. Both Na(1)-O(4) bond lengths are 2.32 Å. Both Na(1)-O(8) bond lengths are 2.54 Å. In the second Na site, Na(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(11), two equivalent O(3), and two equivalent O(5) atoms. Both Na(2)-O(1) bond lengths are 2.61 Å. Both Na(2)-O(11) bond lengths are 2.63 Å. Both Na(2)-O(3) bond lengths are 2.30 Å. Both Na(2)-O(5) bond lengths are 2.61 Å. In the third Na site, Na(3) is bonded in a 8-coordinate geometry to two equivalent O(12), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. Both Na(3)-O(12) bond lengths are 2.56 Å. Both Na(3)-O(2) bond lengths are 2.41 Å. Both Na(3)-O(4) bond lengths are 2.33 Å. Both Na(3)-O(6) bond lengths are 2.64 Å. There are eight inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a distorted square co-planar geometry to two equivalent O(12) and two equivalent O(5) atoms. Both Ta(1)-O(12) bond lengths are 2.02 Å. Both Ta(1)-O(5) bond lengths are 2.02 Å. In the second Ta site, Ta(2) is bonded in a distorted square co-planar geometry to two equivalent O(11) and two equivalent O(6) atoms. Both Ta(2)-O(11) bond lengths are 2.01 Å. Both Ta(2)-O(6) bond lengths are 2.00 Å. In the third Ta site, Ta(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(10) and two equivalent O(7) atoms. Both Ta(3)-O(10) bond lengths are 2.01 Å. Both Ta(3)-O(7) bond lengths are 2.00 Å. In the fourth Ta site, Ta(4) is bonded in a distorted square co-planar geometry to two equivalent O(8) and two equivalent O(9) atoms. Both Ta(4)-O(8) bond lengths are 2.03 Å. Both Ta(4)-O(9) bond lengths are 2.01 Å. In the fifth Ta site, Ta(5) is bonded to one O(11), one O(2), one O(3), one O(6), one O(7), and one O(9) atom to form a mixture of corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 58°. The Ta(5)-O(11) bond length is 2.13 Å. The Ta(5)-O(2) bond length is 1.94 Å. The Ta(5)-O(3) bond length is 1.96 Å. The Ta(5)-O(6) bond length is 2.02 Å. The Ta(5)-O(7) bond length is 2.02 Å. The Ta(5)-O(9) bond length is 2.12 Å. In the sixth Ta site, Ta(6) is bonded to one O(1), one O(10), one O(12), one O(4), one O(5), and one O(8) atom to form a mixture of distorted corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 33°. The Ta(6)-O(1) bond length is 2.02 Å. The Ta(6)-O(10) bond length is 2.15 Å. The Ta(6)-O(12) bond length is 2.15 Å. The Ta(6)-O(4) bond length is 1.97 Å. The Ta(6)-O(5) bond length is 2.02 Å. The Ta(6)-O(8) bond length is 2.01 Å. In the seventh Ta site, Ta(7) is bonded to one O(12), one O(2), one O(4), one O(6), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing TaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 30-70°. The Ta(7)-O(12) bond length is 2.02 Å. The Ta(7)-O(2) bond length is 2.00 Å. The Ta(7)-O(4) bond length is 1.97 Å. The Ta(7)-O(6) bond length is 2.15 Å. The Ta(7)-O(8) bond length is 2.17 Å. The Ta(7)-O(9) bond length is 2.00 Å. In the eighth Ta site, Ta(8) is bonded to one O(1), one O(10), one O(11), one O(3), one O(5), and one O(7) atom to form a mixture of corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 33-58°. The Ta(8)-O(1) bond length is 1.97 Å. The Ta(8)-O(10) bond length is 2.02 Å. The Ta(8)-O(11) bond length is 2.03 Å. The Ta(8)-O(3) bond length is 1.94 Å. The Ta(8)-O(5) bond length is 2.12 Å. The Ta(8)-O(7) bond length is 2.11 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Ta(6), and one Ta(8) atom to form distorted ONa2Ta2 trigonal pyramids that share corners with three equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(12)NaTa3 trigonal pyramid,  a cornercorner with one O(8)NaTa3 trigonal pyramid, corners with two equivalent O(10)NaTa3 trigonal pyramids,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid,  an edgeedge with one O(10)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Na(3), one Ta(5), and one Ta(7) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(2), one Ta(5), and one Ta(8) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ta(6), and one Ta(7) atom to form ONa2Ta2 tetrahedra that share  a cornercorner with one O(10)NaTa3 trigonal pyramid,  a cornercorner with one O(6)NaTa3 trigonal pyramid, corners with two equivalent O(12)NaTa3 trigonal pyramids, corners with two equivalent O(8)NaTa3 trigonal pyramids, corners with three equivalent O(1)Na2Ta2 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(10)NaTa3 trigonal pyramid,  an edgeedge with one O(12)NaTa3 trigonal pyramid,  an edgeedge with one O(6)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(2), one Ta(1), one Ta(6), and one Ta(8) atom. In the sixth O site, O(6) is bonded to one Na(3), one Ta(2), one Ta(5), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share  a cornercorner with one O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(8)NaTa3 trigonal pyramid, corners with three equivalent O(12)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra, and  an edgeedge with one O(6)NaTa3 trigonal pyramid. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Ta(3), one Ta(5), and one Ta(8) atom. In the eighth O site, O(8) is bonded to one Na(1), one Ta(4), one Ta(6), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share corners with two equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(1)Na2Ta2 trigonal pyramid,  a cornercorner with one O(6)NaTa3 trigonal pyramid, corners with three equivalent O(10)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid,  an edgeedge with one O(12)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Ta(4), one Ta(5), and one Ta(7) atom. In the tenth O site, O(10) is bonded to one Na(1), one Ta(3), one Ta(6), and one Ta(8) atom to form distorted ONaTa3 trigonal pyramids that share  a cornercorner with one O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(12)NaTa3 trigonal pyramid, corners with two equivalent O(1)Na2Ta2 trigonal pyramids, corners with three equivalent O(8)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(1)Na2Ta2 trigonal pyramid, and  an edgeedge with one O(10)NaTa3 trigonal pyramid. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Na(2), one Ta(2), one Ta(5), and one Ta(8) atom. In the twelfth O site, O(12) is bonded to one Na(3), one Ta(1), one Ta(6), and one Ta(7) atom to form distorted ONaTa3 trigonal pyramids that share corners with two equivalent O(4)Na2Ta2 tetrahedra,  a cornercorner with one O(1)Na2Ta2 trigonal pyramid,  a cornercorner with one O(10)NaTa3 trigonal pyramid, corners with three equivalent O(6)NaTa3 trigonal pyramids,  an edgeedge with one O(4)Na2Ta2 tetrahedra,  an edgeedge with one O(12)NaTa3 trigonal pyramid, and  an edgeedge with one O(8)NaTa3 trigonal pyramid.