Cr8O21 crystallizes in the triclinic P-1 space group. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(3), one O(5), and one O(8) atom to form distorted corner-sharing CrO4 tetrahedra. In the second Cr site, Cr(2) is bonded in a distorted hexagonal planar geometry to one O(11), one O(4), one O(6), one O(7), and two equivalent O(1) atoms. In the third Cr site, Cr(3) is bonded to one O(3), one O(6), one O(7), and one O(9) atom to form distorted corner-sharing CrO4 tetrahedra. In the fourth Cr site, Cr(4) is bonded in a distorted tetrahedral geometry to one O(1), one O(11), one O(2), and one O(4) atom. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cr(4) and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a single-bond geometry to one Cr(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cr(1) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(4) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Cr(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the eighth O site, O(8) is bonded in a single-bond geometry to one Cr(1) atom. In the ninth O site, O(9) is bonded in a single-bond geometry to one Cr(3) atom. In the tenth O site, O(10) is bonded in a linear geometry to two equivalent Cr(1) atoms. In the eleventh O site, O(11) is bonded in a linear geometry to one Cr(2) and one Cr(4) atom.
Cr8O21 crystallizes in the triclinic P-1 space group. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(3), one O(5), and one O(8) atom to form distorted corner-sharing CrO4 tetrahedra. The Cr(1)-O(10) bond length is 1.64 Å. The Cr(1)-O(3) bond length is 1.41 Å. The Cr(1)-O(5) bond length is 1.77 Å. The Cr(1)-O(8) bond length is 2.04 Å. In the second Cr site, Cr(2) is bonded in a distorted hexagonal planar geometry to one O(11), one O(4), one O(6), one O(7), and two equivalent O(1) atoms. The Cr(2)-O(11) bond length is 2.11 Å. The Cr(2)-O(4) bond length is 1.99 Å. The Cr(2)-O(6) bond length is 2.07 Å. The Cr(2)-O(7) bond length is 2.13 Å. There is one shorter (2.17 Å) and one longer (2.23 Å) Cr(2)-O(1) bond length. In the third Cr site, Cr(3) is bonded to one O(3), one O(6), one O(7), and one O(9) atom to form distorted corner-sharing CrO4 tetrahedra. The Cr(3)-O(3) bond length is 1.65 Å. The Cr(3)-O(6) bond length is 1.70 Å. The Cr(3)-O(7) bond length is 2.00 Å. The Cr(3)-O(9) bond length is 1.64 Å. In the fourth Cr site, Cr(4) is bonded in a distorted tetrahedral geometry to one O(1), one O(11), one O(2), and one O(4) atom. The Cr(4)-O(1) bond length is 1.59 Å. The Cr(4)-O(11) bond length is 1.70 Å. The Cr(4)-O(2) bond length is 1.88 Å. The Cr(4)-O(4) bond length is 1.79 Å. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cr(4) and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a single-bond geometry to one Cr(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cr(1) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(4) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Cr(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the eighth O site, O(8) is bonded in a single-bond geometry to one Cr(1) atom. In the ninth O site, O(9) is bonded in a single-bond geometry to one Cr(3) atom. In the tenth O site, O(10) is bonded in a linear geometry to two equivalent Cr(1) atoms. In the eleventh O site, O(11) is bonded in a linear geometry to one Cr(2) and one Cr(4) atom.