K2ErCPO7 crystallizes in the monoclinic P2_1/m space group. K(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms. Er(1) is bonded to one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms to form ErO6 octahedra that share corners with four equivalent P(1)O4 tetrahedra. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(3) atom. P(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form PO4 tetrahedra that share corners with four equivalent Er(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-43°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent K(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Er(1), and one C(1) atom. In the third O site, O(3) is bonded in a distorted trigonal pyramidal geometry to two equivalent K(1), one Er(1), and one C(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom.
K2ErCPO7 crystallizes in the monoclinic P2_1/m space group. K(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms. The K(1)-O(1) bond length is 2.53 Å. The K(1)-O(2) bond length is 2.67 Å. The K(1)-O(3) bond length is 2.65 Å. The K(1)-O(5) bond length is 2.83 Å. The K(1)-O(6) bond length is 3.04 Å. There is one shorter (3.05 Å) and one longer (3.26 Å) K(1)-O(4) bond length. Er(1) is bonded to one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms to form ErO6 octahedra that share corners with four equivalent P(1)O4 tetrahedra. The Er(1)-O(2) bond length is 2.32 Å. The Er(1)-O(3) bond length is 2.27 Å. The Er(1)-O(5) bond length is 2.21 Å. The Er(1)-O(6) bond length is 2.22 Å. Both Er(1)-O(4) bond lengths are 2.28 Å. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(3) atom. The C(1)-O(1) bond length is 1.25 Å. The C(1)-O(2) bond length is 1.32 Å. The C(1)-O(3) bond length is 1.33 Å. P(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form PO4 tetrahedra that share corners with four equivalent Er(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-43°. The P(1)-O(5) bond length is 1.57 Å. The P(1)-O(6) bond length is 1.57 Å. Both P(1)-O(4) bond lengths are 1.55 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent K(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent K(1), one Er(1), and one C(1) atom. In the third O site, O(3) is bonded in a distorted trigonal pyramidal geometry to two equivalent K(1), one Er(1), and one C(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to two equivalent K(1), one Er(1), and one P(1) atom.