KErP2S7 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded to one S(3), one S(6), two equivalent S(1), two equivalent S(5), and two equivalent S(7) atoms to form distorted KS8 hexagonal bipyramids that share  a cornercorner with one P(2)S4 tetrahedra, corners with four equivalent P(1)S4 tetrahedra, edges with three equivalent K(1)S8 hexagonal bipyramids, and edges with two equivalent P(2)S4 tetrahedra. Er(1) is bonded in a 8-coordinate geometry to one S(1), one S(3), one S(5), one S(7), two equivalent S(2), and two equivalent S(4) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded to one S(1), one S(3), one S(4), and one S(6) atom to form PS4 tetrahedra that share corners with four equivalent K(1)S8 hexagonal bipyramids and  a cornercorner with one P(2)S4 tetrahedra. In the second P site, P(2) is bonded to one S(2), one S(5), one S(6), and one S(7) atom to form PS4 tetrahedra that share  a cornercorner with one K(1)S8 hexagonal bipyramid,  a cornercorner with one P(1)S4 tetrahedra, and edges with two equivalent K(1)S8 hexagonal bipyramids. There are seven inequivalent S sites. In the first S site, S(1) is bonded to two equivalent K(1), one Er(1), and one P(1) atom to form distorted corner-sharing SK2ErP trigonal pyramids. In the second S site, S(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one P(2) atom. In the third S site, S(3) is bonded in a 3-coordinate geometry to one K(1), one Er(1), and one P(1) atom. In the fourth S site, S(4) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one P(1) atom. In the fifth S site, S(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Er(1), and one P(2) atom. In the sixth S site, S(6) is bonded in a 3-coordinate geometry to one K(1), one P(1), and one P(2) atom. In the seventh S site, S(7) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(2) atom.
KErP2S7 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded to one S(3), one S(6), two equivalent S(1), two equivalent S(5), and two equivalent S(7) atoms to form distorted KS8 hexagonal bipyramids that share  a cornercorner with one P(2)S4 tetrahedra, corners with four equivalent P(1)S4 tetrahedra, edges with three equivalent K(1)S8 hexagonal bipyramids, and edges with two equivalent P(2)S4 tetrahedra. The K(1)-S(3) bond length is 3.42 Å. The K(1)-S(6) bond length is 3.59 Å. There is one shorter (3.31 Å) and one longer (3.43 Å) K(1)-S(1) bond length. There is one shorter (3.45 Å) and one longer (3.46 Å) K(1)-S(5) bond length. There is one shorter (3.35 Å) and one longer (3.45 Å) K(1)-S(7) bond length. Er(1) is bonded in a 8-coordinate geometry to one S(1), one S(3), one S(5), one S(7), two equivalent S(2), and two equivalent S(4) atoms. The Er(1)-S(1) bond length is 2.84 Å. The Er(1)-S(3) bond length is 2.91 Å. The Er(1)-S(5) bond length is 2.86 Å. The Er(1)-S(7) bond length is 2.75 Å. There is one shorter (2.89 Å) and one longer (3.10 Å) Er(1)-S(2) bond length. There is one shorter (2.83 Å) and one longer (2.89 Å) Er(1)-S(4) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one S(1), one S(3), one S(4), and one S(6) atom to form PS4 tetrahedra that share corners with four equivalent K(1)S8 hexagonal bipyramids and  a cornercorner with one P(2)S4 tetrahedra. The P(1)-S(1) bond length is 2.03 Å. The P(1)-S(3) bond length is 2.02 Å. The P(1)-S(4) bond length is 2.04 Å. The P(1)-S(6) bond length is 2.15 Å. In the second P site, P(2) is bonded to one S(2), one S(5), one S(6), and one S(7) atom to form PS4 tetrahedra that share  a cornercorner with one K(1)S8 hexagonal bipyramid,  a cornercorner with one P(1)S4 tetrahedra, and edges with two equivalent K(1)S8 hexagonal bipyramids. The P(2)-S(2) bond length is 2.03 Å. The P(2)-S(5) bond length is 2.04 Å. The P(2)-S(6) bond length is 2.14 Å. The P(2)-S(7) bond length is 2.03 Å. There are seven inequivalent S sites. In the first S site, S(1) is bonded to two equivalent K(1), one Er(1), and one P(1) atom to form distorted corner-sharing SK2ErP trigonal pyramids. In the second S site, S(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one P(2) atom. In the third S site, S(3) is bonded in a 3-coordinate geometry to one K(1), one Er(1), and one P(1) atom. In the fourth S site, S(4) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one P(1) atom. In the fifth S site, S(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Er(1), and one P(2) atom. In the sixth S site, S(6) is bonded in a 3-coordinate geometry to one K(1), one P(1), and one P(2) atom. In the seventh S site, S(7) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(2) atom.