K2Nb4Fe2O13 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 6-coordinate geometry to two equivalent O(4), two equivalent O(5), and two equivalent O(7) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(5), one O(6), one O(7), and three equivalent O(3) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 33°. In the second Nb site, Nb(2) is bonded to one O(2), one O(4), one O(5), one O(6), and two equivalent O(1) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-16°. Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(7), and two equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent Nb(2) and one Fe(1) atom. In the second O site, O(2) is bonded in a linear geometry to two equivalent Nb(2) atoms. In the third O site, O(3) is bonded to three equivalent Nb(1) and one Fe(1) atom to form distorted ONb3Fe trigonal pyramids that share  a cornercorner with one O(6)Nb2Fe2 tetrahedra, corners with two equivalent O(3)Nb3Fe trigonal pyramids, edges with two equivalent O(6)Nb2Fe2 tetrahedra, and edges with two equivalent O(3)Nb3Fe trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent K(1), one Nb(2), and one Fe(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded to one Nb(1), one Nb(2), and two equivalent Fe(1) atoms to form ONb2Fe2 tetrahedra that share corners with two equivalent O(6)Nb2Fe2 tetrahedra,  a cornercorner with one O(3)Nb3Fe trigonal pyramid, and edges with two equivalent O(3)Nb3Fe trigonal pyramids. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Nb(1), and one Fe(1) atom.
K2Nb4Fe2O13 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 6-coordinate geometry to two equivalent O(4), two equivalent O(5), and two equivalent O(7) atoms. Both K(1)-O(4) bond lengths are 3.00 Å. Both K(1)-O(5) bond lengths are 2.77 Å. Both K(1)-O(7) bond lengths are 2.85 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(5), one O(6), one O(7), and three equivalent O(3) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 33°. The Nb(1)-O(5) bond length is 1.84 Å. The Nb(1)-O(6) bond length is 2.24 Å. The Nb(1)-O(7) bond length is 1.85 Å. There are two shorter (2.07 Å) and one longer (2.34 Å) Nb(1)-O(3) bond length. In the second Nb site, Nb(2) is bonded to one O(2), one O(4), one O(5), one O(6), and two equivalent O(1) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-16°. The Nb(2)-O(2) bond length is 1.98 Å. The Nb(2)-O(4) bond length is 1.84 Å. The Nb(2)-O(5) bond length is 2.40 Å. The Nb(2)-O(6) bond length is 2.07 Å. Both Nb(2)-O(1) bond lengths are 2.00 Å. Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(7), and two equivalent O(6) atoms. The Fe(1)-O(1) bond length is 2.33 Å. The Fe(1)-O(3) bond length is 2.46 Å. The Fe(1)-O(4) bond length is 2.02 Å. The Fe(1)-O(7) bond length is 2.14 Å. Both Fe(1)-O(6) bond lengths are 2.10 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent Nb(2) and one Fe(1) atom. In the second O site, O(2) is bonded in a linear geometry to two equivalent Nb(2) atoms. In the third O site, O(3) is bonded to three equivalent Nb(1) and one Fe(1) atom to form distorted ONb3Fe trigonal pyramids that share  a cornercorner with one O(6)Nb2Fe2 tetrahedra, corners with two equivalent O(3)Nb3Fe trigonal pyramids, edges with two equivalent O(6)Nb2Fe2 tetrahedra, and edges with two equivalent O(3)Nb3Fe trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent K(1), one Nb(2), and one Fe(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded to one Nb(1), one Nb(2), and two equivalent Fe(1) atoms to form ONb2Fe2 tetrahedra that share corners with two equivalent O(6)Nb2Fe2 tetrahedra,  a cornercorner with one O(3)Nb3Fe trigonal pyramid, and edges with two equivalent O(3)Nb3Fe trigonal pyramids. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Nb(1), and one Fe(1) atom.