C4H4O6HK crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one H(3), one O(3), one O(6), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. The K(1)-H(3) bond length is 2.97 Å. The K(1)-O(3) bond length is 2.79 Å. The K(1)-O(6) bond length is 3.12 Å. There is one shorter (2.86 Å) and one longer (2.88 Å) K(1)-O(2) bond length. There is one shorter (2.85 Å) and one longer (3.06 Å) K(1)-O(4) bond length. There is one shorter (2.80 Å) and one longer (2.81 Å) K(1)-O(5) bond length. There are four inequivalent C sites. In the first C site, C(3) is bonded in a distorted water-like geometry to one H(3) and one O(4) atom. The C(3)-H(3) bond length is 1.10 Å. The C(3)-O(4) bond length is 1.42 Å. In the second C site, C(4) is bonded in a distorted bent 120 degrees geometry to one O(5) and one O(6) atom. The C(4)-O(5) bond length is 1.24 Å. The C(4)-O(6) bond length is 1.32 Å. In the third C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(2) atom. The C(1)-O(1) bond length is 1.28 Å. The C(1)-O(2) bond length is 1.26 Å. In the fourth C site, C(2) is bonded in a distorted water-like geometry to one H(2) and one O(3) atom. The C(2)-H(2) bond length is 1.10 Å. The C(2)-O(3) bond length is 1.42 Å. There are five inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(1) and one O(6) atom. The H(1)-O(1) bond length is 1.47 Å. The H(1)-O(6) bond length is 1.06 Å. In the second H site, H(2) is bonded in a single-bond geometry to one C(2) atom. In the third H site, H(3) is bonded in a single-bond geometry to one K(1) and one C(3) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(4) atom. The H(4)-O(4) bond length is 1.00 Å. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(3) atom. The H(5)-O(3) bond length is 0.99 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one C(1) and one H(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to two equivalent K(1) and one C(1) atom. In the third O site, O(6) is bonded in a distorted water-like geometry to one K(1), one C(4), and one H(1) atom. In the fourth O site, O(3) is bonded in a distorted water-like geometry to one K(1), one C(2), and one H(5) atom. In the fifth O site, O(4) is bonded in a distorted water-like geometry to two equivalent K(1), one C(3), and one H(4) atom. In the sixth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent K(1) and one C(4) atom. Linkers: 2 [O]C(=O)[C@@H](O)[C@H](O)C(=O)O ,2 [O]C(=O)[C@H](O)[C@@H](O)C(=O)O. Metal clusters: 4 [K]. The MOF has largest included sphere 1.62 A, density 1.95 g/cm3, surface area 1373.93 m2/g, accessible volume 0.02 cm3/g