KSb2PO8 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(7) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra, corners with two equivalent Sb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-51°. In the second Sb site, Sb(2) is bonded to one O(1), one O(2), one O(4), one O(8), and two equivalent O(6) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one Sb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-51°. P(1) is bonded to one O(1), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Sb(1)O6 octahedra and corners with two equivalent Sb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-53°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Sb(2) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one K(1), one Sb(1), and one Sb(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one K(1), one Sb(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one K(1), one Sb(1), and one Sb(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one Sb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Sb(2) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Sb(1) atoms. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one K(1), one Sb(2), and one P(1) atom.
KSb2PO8 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. The K(1)-O(2) bond length is 2.79 Å. The K(1)-O(3) bond length is 2.99 Å. The K(1)-O(4) bond length is 2.80 Å. The K(1)-O(5) bond length is 2.98 Å. The K(1)-O(8) bond length is 3.28 Å. There is one shorter (2.86 Å) and one longer (3.33 Å) K(1)-O(6) bond length. There is one shorter (2.96 Å) and one longer (3.10 Å) K(1)-O(7) bond length. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(7) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra, corners with two equivalent Sb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-51°. The Sb(1)-O(2) bond length is 1.95 Å. The Sb(1)-O(3) bond length is 2.03 Å. The Sb(1)-O(4) bond length is 1.94 Å. The Sb(1)-O(5) bond length is 2.04 Å. There is one shorter (1.95 Å) and one longer (1.96 Å) Sb(1)-O(7) bond length. In the second Sb site, Sb(2) is bonded to one O(1), one O(2), one O(4), one O(8), and two equivalent O(6) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one Sb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-51°. The Sb(2)-O(1) bond length is 2.07 Å. The Sb(2)-O(2) bond length is 1.93 Å. The Sb(2)-O(4) bond length is 1.96 Å. The Sb(2)-O(8) bond length is 2.00 Å. There is one shorter (1.97 Å) and one longer (2.00 Å) Sb(2)-O(6) bond length. P(1) is bonded to one O(1), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Sb(1)O6 octahedra and corners with two equivalent Sb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-53°. The P(1)-O(1) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(8) bond length is 1.52 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Sb(2) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one K(1), one Sb(1), and one Sb(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one K(1), one Sb(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one K(1), one Sb(1), and one Sb(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one Sb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Sb(2) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Sb(1) atoms. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one K(1), one Sb(2), and one P(1) atom.