KNb2PO8 crystallizes in the trigonal R3 space group. K(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-38°. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(3), one O(7), and two equivalent O(8) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-39°. P(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 36-41°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one K(1), one Nb(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one K(1), one Nb(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one K(1), one Nb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one K(1), one Nb(2), and one P(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Nb(2) atoms.
KNb2PO8 crystallizes in the trigonal R3 space group. K(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom. The K(1)-O(1) bond length is 3.24 Å. The K(1)-O(3) bond length is 3.29 Å. The K(1)-O(4) bond length is 3.05 Å. The K(1)-O(5) bond length is 2.91 Å. The K(1)-O(7) bond length is 3.26 Å. The K(1)-O(8) bond length is 3.12 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-38°. The Nb(1)-O(1) bond length is 1.97 Å. The Nb(1)-O(2) bond length is 1.95 Å. The Nb(1)-O(5) bond length is 2.13 Å. The Nb(1)-O(6) bond length is 2.10 Å. There is one shorter (1.89 Å) and one longer (2.05 Å) Nb(1)-O(4) bond length. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(3), one O(7), and two equivalent O(8) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-39°. The Nb(2)-O(1) bond length is 1.98 Å. The Nb(2)-O(2) bond length is 1.92 Å. The Nb(2)-O(3) bond length is 2.12 Å. The Nb(2)-O(7) bond length is 2.13 Å. There is one shorter (1.90 Å) and one longer (2.04 Å) Nb(2)-O(8) bond length. P(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 36-41°. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.55 Å. The P(1)-O(6) bond length is 1.55 Å. The P(1)-O(7) bond length is 1.54 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one K(1), one Nb(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one K(1), one Nb(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one K(1), one Nb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one K(1), one Nb(2), and one P(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Nb(2) atoms.