K4C2O9 crystallizes in the monoclinic C2/c space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(5), and four equivalent O(3) atoms. In the third K site, K(3) is bonded in a 8-coordinate geometry to one O(2), one O(3), two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(3) is bonded to one K(1), one K(3), and two equivalent K(2) atoms to form a mixture of distorted corner and edge-sharing OK4 trigonal pyramids. In the second O site, O(4) is bonded to four equivalent K(3) atoms to form a mixture of distorted corner and edge-sharing OK4 trigonal pyramids. In the third O site, O(5) is bonded in a distorted single-bond geometry to one K(1), one K(2), two equivalent K(3), and one C(1) atom. In the fourth O site, O(1) is bonded in a distorted single-bond geometry to one K(1), one K(2), two equivalent K(3), and one C(1) atom. In the fifth O site, O(2) is bonded in a single-bond geometry to one K(1), one K(3), and one C(1) atom.
K4C2O9 crystallizes in the monoclinic C2/c space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. Both K(1)-O(1) bond lengths are 2.81 Å. Both K(1)-O(2) bond lengths are 3.13 Å. Both K(1)-O(3) bond lengths are 2.79 Å. Both K(1)-O(5) bond lengths are 2.81 Å. In the second K site, K(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(5), and four equivalent O(3) atoms. Both K(2)-O(1) bond lengths are 2.80 Å. Both K(2)-O(5) bond lengths are 2.76 Å. All K(2)-O(3) bond lengths are 2.79 Å. In the third K site, K(3) is bonded in a 8-coordinate geometry to one O(2), one O(3), two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms. The K(3)-O(2) bond length is 2.80 Å. The K(3)-O(3) bond length is 2.75 Å. There is one shorter (3.03 Å) and one longer (3.08 Å) K(3)-O(1) bond length. There is one shorter (2.78 Å) and one longer (2.90 Å) K(3)-O(4) bond length. There is one shorter (2.86 Å) and one longer (3.09 Å) K(3)-O(5) bond length. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(5) atom. The C(1)-O(1) bond length is 1.30 Å. The C(1)-O(2) bond length is 1.31 Å. The C(1)-O(5) bond length is 1.28 Å. There are five inequivalent O sites. In the first O site, O(3) is bonded to one K(1), one K(3), and two equivalent K(2) atoms to form a mixture of distorted corner and edge-sharing OK4 trigonal pyramids. In the second O site, O(4) is bonded to four equivalent K(3) atoms to form a mixture of distorted corner and edge-sharing OK4 trigonal pyramids. In the third O site, O(5) is bonded in a distorted single-bond geometry to one K(1), one K(2), two equivalent K(3), and one C(1) atom. In the fourth O site, O(1) is bonded in a distorted single-bond geometry to one K(1), one K(2), two equivalent K(3), and one C(1) atom. In the fifth O site, O(2) is bonded in a single-bond geometry to one K(1), one K(3), and one C(1) atom.