K3Nb3Si2O13 crystallizes in the hexagonal P-62m space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(3), and eight equivalent O(2) atoms. In the second K site, K(2) is bonded in a 15-coordinate geometry to two equivalent O(3), two equivalent O(4), three equivalent O(5), and eight equivalent O(2) atoms. Nb(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 3-31°. Si(1) is bonded to one O(4) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 23°. There are five inequivalent O sites. In the first O site, O(4) is bonded in a linear geometry to three equivalent K(2) and two equivalent Si(1) atoms. In the second O site, O(5) is bonded in a distorted linear geometry to three equivalent K(2) and two equivalent Nb(1) atoms. In the third O site, O(1) is bonded in a linear geometry to two equivalent K(1) and two equivalent Nb(1) atoms. In the fourth O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1), two equivalent K(2), one Nb(1), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one K(1), one K(2), and two equivalent Nb(1) atoms.
K3Nb3Si2O13 crystallizes in the hexagonal P-62m space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(3), and eight equivalent O(2) atoms. Both K(1)-O(1) bond lengths are 3.25 Å. Both K(1)-O(3) bond lengths are 2.99 Å. There are four shorter (2.98 Å) and four longer (3.11 Å) K(1)-O(2) bond lengths. In the second K site, K(2) is bonded in a 15-coordinate geometry to two equivalent O(3), two equivalent O(4), three equivalent O(5), and eight equivalent O(2) atoms. Both K(2)-O(3) bond lengths are 2.73 Å. Both K(2)-O(4) bond lengths are 2.86 Å. There is one shorter (3.15 Å) and two longer (3.20 Å) K(2)-O(5) bond lengths. There are four shorter (3.28 Å) and four longer (3.29 Å) K(2)-O(2) bond lengths. Nb(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 3-31°. The Nb(1)-O(1) bond length is 1.98 Å. The Nb(1)-O(5) bond length is 2.01 Å. Both Nb(1)-O(2) bond lengths are 2.07 Å. Both Nb(1)-O(3) bond lengths are 1.98 Å. Si(1) is bonded to one O(4) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 23°. The Si(1)-O(4) bond length is 1.66 Å. All Si(1)-O(2) bond lengths are 1.62 Å. There are five inequivalent O sites. In the first O site, O(4) is bonded in a linear geometry to three equivalent K(2) and two equivalent Si(1) atoms. In the second O site, O(5) is bonded in a distorted linear geometry to three equivalent K(2) and two equivalent Nb(1) atoms. In the third O site, O(1) is bonded in a linear geometry to two equivalent K(1) and two equivalent Nb(1) atoms. In the fourth O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1), two equivalent K(2), one Nb(1), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one K(1), one K(2), and two equivalent Nb(1) atoms.