KNb4O5F crystallizes in the tetragonal P4/mmm space group. K(1) is bonded to eight equivalent O(1) and four equivalent F(1) atoms to form KO8F4 cuboctahedra that share corners with four equivalent K(1)O8F4 cuboctahedra, faces with four equivalent K(1)O8F4 cuboctahedra, and faces with eight equivalent Nb(1)O4F square pyramids. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to four equivalent O(1) and one F(1) atom to form NbO4F square pyramids that share corners with five equivalent Nb(1)O4F square pyramids and faces with four equivalent K(1)O8F4 cuboctahedra. In the second Nb site, Nb(2) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent K(1), one Nb(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a square co-planar geometry to four equivalent Nb(2) atoms. F(1) is bonded to four equivalent K(1) and two equivalent Nb(1) atoms to form a mixture of distorted corner and edge-sharing FK4Nb2 octahedra. The corner-sharing octahedra are not tilted.
KNb4O5F crystallizes in the tetragonal P4/mmm space group. K(1) is bonded to eight equivalent O(1) and four equivalent F(1) atoms to form KO8F4 cuboctahedra that share corners with four equivalent K(1)O8F4 cuboctahedra, faces with four equivalent K(1)O8F4 cuboctahedra, and faces with eight equivalent Nb(1)O4F square pyramids. All K(1)-O(1) bond lengths are 2.96 Å. All K(1)-F(1) bond lengths are 2.97 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to four equivalent O(1) and one F(1) atom to form NbO4F square pyramids that share corners with five equivalent Nb(1)O4F square pyramids and faces with four equivalent K(1)O8F4 cuboctahedra. All Nb(1)-O(1) bond lengths are 2.10 Å. The Nb(1)-F(1) bond length is 2.21 Å. In the second Nb site, Nb(2) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Nb(2)-O(1) bond lengths are 2.12 Å. Both Nb(2)-O(2) bond lengths are 2.10 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent K(1), one Nb(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a square co-planar geometry to four equivalent Nb(2) atoms. F(1) is bonded to four equivalent K(1) and two equivalent Nb(1) atoms to form a mixture of distorted corner and edge-sharing FK4Nb2 octahedra. The corner-sharing octahedra are not tilted.