KC4H5O3 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one H(5), two equivalent H(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. The K(1)-H(5) bond length is 2.92 Å. There is one shorter (2.71 Å) and one longer (2.92 Å) K(1)-H(4) bond length. There is one shorter (2.80 Å) and one longer (2.83 Å) K(1)-O(1) bond length. There is one shorter (2.70 Å) and one longer (3.04 Å) K(1)-O(2) bond length. There is one shorter (2.70 Å) and one longer (2.79 Å) K(1)-O(3) bond length. There are four inequivalent C sites. In the first C site, C(3) is bonded in a distorted single-bond geometry to one C(2) and one O(1) atom. The C(3)-C(2) bond length is 1.41 Å. The C(3)-O(1) bond length is 1.28 Å. In the second C site, C(4) is bonded in a distorted single-bond geometry to one C(2) and one O(2) atom. The C(4)-C(2) bond length is 1.41 Å. The C(4)-O(2) bond length is 1.28 Å. In the third C site, C(1) is bonded in a distorted trigonal non-coplanar geometry to one C(2), one H(1), one H(2), and one H(3) atom. The C(1)-C(2) bond length is 1.50 Å. The C(1)-H(1) bond length is 1.10 Å. The C(1)-H(2) bond length is 1.10 Å. The C(1)-H(3) bond length is 1.09 Å. In the fourth C site, C(2) is bonded in a trigonal planar geometry to one C(1), one C(3), and one C(4) atom. There are five inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(1) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(1) atom. In the fourth H site, H(4) is bonded in a distorted single-bond geometry to two equivalent K(1) and one O(3) atom. The H(4)-O(3) bond length is 1.00 Å. In the fifth H site, H(5) is bonded in a single-bond geometry to one K(1) and one O(3) atom. The H(5)-O(3) bond length is 0.99 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent K(1) and one C(3) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent K(1) and one C(4) atom. In the third O site, O(3) is bonded in a water-like geometry to two equivalent K(1), one H(4), and one H(5) atom. Linkers: 2 C[C]1C(=O)C(=O)[C](C)C(=O)C1=O ,2 [CH2][C]1C(=O)C(=O)[C](C)C(=O)C1=O. Metal clusters: 4 [K]. The MOF has largest included sphere 1.22 A, density 1.78 g/cm3, surface area 1667.84 m2/g, accessible volume 0.02 cm3/g