K2ErSbO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms to form KO8 hexagonal bipyramids that share corners with two equivalent K(1)O8 hexagonal bipyramids, corners with two equivalent Sb(1)O6 octahedra, edges with four equivalent K(2)O8 hexagonal bipyramids, edges with two equivalent Sb(1)O6 octahedra, and edges with four equivalent Er(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. In the second K site, K(2) is bonded to four equivalent O(1) and four equivalent O(2) atoms to form distorted KO8 hexagonal bipyramids that share edges with two equivalent K(2)O8 hexagonal bipyramids, edges with four equivalent K(1)O8 hexagonal bipyramids, edges with two equivalent Er(1)O6 octahedra, and edges with four equivalent Sb(1)O6 octahedra. Er(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form ErO6 octahedra that share corners with two equivalent Er(1)O6 octahedra, corners with four equivalent Sb(1)O6 octahedra, edges with two equivalent K(2)O8 hexagonal bipyramids, and edges with four equivalent K(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-49°. Sb(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form SbO6 octahedra that share corners with two equivalent K(1)O8 hexagonal bipyramids, corners with four equivalent Er(1)O6 octahedra, edges with two equivalent K(1)O8 hexagonal bipyramids, and edges with four equivalent K(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 34°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one K(1), two equivalent K(2), and one Sb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Er(1), and one Sb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1) and two equivalent Er(1) atoms.
K2ErSbO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms to form KO8 hexagonal bipyramids that share corners with two equivalent K(1)O8 hexagonal bipyramids, corners with two equivalent Sb(1)O6 octahedra, edges with four equivalent K(2)O8 hexagonal bipyramids, edges with two equivalent Sb(1)O6 octahedra, and edges with four equivalent Er(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Both K(1)-O(1) bond lengths are 2.65 Å. Both K(1)-O(3) bond lengths are 3.08 Å. All K(1)-O(2) bond lengths are 2.95 Å. In the second K site, K(2) is bonded to four equivalent O(1) and four equivalent O(2) atoms to form distorted KO8 hexagonal bipyramids that share edges with two equivalent K(2)O8 hexagonal bipyramids, edges with four equivalent K(1)O8 hexagonal bipyramids, edges with two equivalent Er(1)O6 octahedra, and edges with four equivalent Sb(1)O6 octahedra. All K(2)-O(1) bond lengths are 2.77 Å. All K(2)-O(2) bond lengths are 3.16 Å. Er(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form ErO6 octahedra that share corners with two equivalent Er(1)O6 octahedra, corners with four equivalent Sb(1)O6 octahedra, edges with two equivalent K(2)O8 hexagonal bipyramids, and edges with four equivalent K(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-49°. Both Er(1)-O(3) bond lengths are 2.21 Å. All Er(1)-O(2) bond lengths are 2.25 Å. Sb(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form SbO6 octahedra that share corners with two equivalent K(1)O8 hexagonal bipyramids, corners with four equivalent Er(1)O6 octahedra, edges with two equivalent K(1)O8 hexagonal bipyramids, and edges with four equivalent K(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 34°. Both Sb(1)-O(1) bond lengths are 1.97 Å. All Sb(1)-O(2) bond lengths are 2.00 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one K(1), two equivalent K(2), and one Sb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Er(1), and one Sb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent K(1) and two equivalent Er(1) atoms.