K2Cr3O9 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 11-coordinate geometry to one O(3), one O(5), two equivalent O(1), three equivalent O(4), and four equivalent O(6) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to one O(4), one O(7), two equivalent O(1), and two equivalent O(6) atoms. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, and edges with two equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. In the third Cr site, Cr(3) is bonded to one O(2), one O(7), and two equivalent O(6) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cr(3) and two equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a water-like geometry to one K(1) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a single-bond geometry to one K(2), three equivalent K(1), and one Cr(2) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one K(1) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Cr(3) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one K(2) and one Cr(3) atom.
K2Cr3O9 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 11-coordinate geometry to one O(3), one O(5), two equivalent O(1), three equivalent O(4), and four equivalent O(6) atoms. The K(1)-O(3) bond length is 3.00 Å. The K(1)-O(5) bond length is 3.02 Å. Both K(1)-O(1) bond lengths are 3.12 Å. There are two shorter (3.10 Å) and one longer (3.13 Å) K(1)-O(4) bond length. There are two shorter (2.74 Å) and two longer (2.94 Å) K(1)-O(6) bond lengths. In the second K site, K(2) is bonded in a 6-coordinate geometry to one O(4), one O(7), two equivalent O(1), and two equivalent O(6) atoms. The K(2)-O(4) bond length is 2.88 Å. The K(2)-O(7) bond length is 2.76 Å. Both K(2)-O(1) bond lengths are 2.84 Å. Both K(2)-O(6) bond lengths are 2.73 Å. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, and edges with two equivalent Cr(1)O6 octahedra. Both Cr(1)-O(1) bond lengths are 1.99 Å. Both Cr(1)-O(2) bond lengths are 2.05 Å. Both Cr(1)-O(3) bond lengths are 1.86 Å. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. The Cr(2)-O(4) bond length is 1.63 Å. The Cr(2)-O(5) bond length is 1.63 Å. Both Cr(2)-O(1) bond lengths are 1.71 Å. In the third Cr site, Cr(3) is bonded to one O(2), one O(7), and two equivalent O(6) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. The Cr(3)-O(2) bond length is 1.81 Å. The Cr(3)-O(7) bond length is 1.62 Å. Both Cr(3)-O(6) bond lengths are 1.63 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cr(3) and two equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a water-like geometry to one K(1) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a single-bond geometry to one K(2), three equivalent K(1), and one Cr(2) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one K(1) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Cr(3) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one K(2) and one Cr(3) atom.