KNaC4H10O9 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The K(1)-O(1) bond length is 3.03 Å. The K(1)-O(3) bond length is 2.91 Å. The K(1)-O(4) bond length is 2.78 Å. The K(1)-O(5) bond length is 2.83 Å. The K(1)-O(6) bond length is 2.91 Å. The K(1)-O(7) bond length is 2.96 Å. The K(1)-O(8) bond length is 2.95 Å. The K(1)-O(9) bond length is 2.88 Å. Na(1) is bonded to one O(2), one O(3), one O(5), one O(9), and two equivalent O(4) atoms to form distorted edge-sharing NaO6 octahedra. The Na(1)-O(2) bond length is 2.39 Å. The Na(1)-O(3) bond length is 2.33 Å. The Na(1)-O(5) bond length is 2.37 Å. The Na(1)-O(9) bond length is 2.44 Å. There is one shorter (2.39 Å) and one longer (2.56 Å) Na(1)-O(4) bond length. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(4) and one O(7) atom. The C(1)-O(4) bond length is 1.26 Å. The C(1)-O(7) bond length is 1.28 Å. In the second C site, C(2) is bonded in a distorted water-like geometry to one H(8) and one O(3) atom. The C(2)-H(8) bond length is 1.10 Å. The C(2)-O(3) bond length is 1.42 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(6) atom. The C(3)-O(1) bond length is 1.27 Å. The C(3)-O(6) bond length is 1.27 Å. In the fourth C site, C(4) is bonded in a distorted water-like geometry to one H(4) and one O(9) atom. The C(4)-H(4) bond length is 1.10 Å. The C(4)-O(9) bond length is 1.42 Å. There are ten inequivalent H sites. In the first H site, H(1) is bonded in a distorted single-bond geometry to one O(8) and one O(9) atom. The H(1)-O(8) bond length is 1.59 Å. The H(1)-O(9) bond length is 1.02 Å. In the second H site, H(2) is bonded in a distorted single-bond geometry to one O(8) atom. The H(2)-O(8) bond length is 1.01 Å. In the third H site, H(3) is bonded in a single-bond geometry to one O(5) atom. The H(3)-O(5) bond length is 0.99 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(4) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(8) atom. The H(5)-O(8) bond length is 0.99 Å. In the sixth H site, H(6) is bonded in a distorted linear geometry to one O(1) and one O(3) atom. The H(6)-O(1) bond length is 1.59 Å. The H(6)-O(3) bond length is 1.01 Å. In the seventh H site, H(7) is bonded in a single-bond geometry to one O(5) atom. The H(7)-O(5) bond length is 0.99 Å. In the eighth H site, H(8) is bonded in a single-bond geometry to one C(2) atom. In the ninth H site, H(9) is bonded in a single-bond geometry to one O(2) atom. The H(9)-O(2) bond length is 1.00 Å. In the tenth H site, H(10) is bonded in a single-bond geometry to one O(2) atom. The H(10)-O(2) bond length is 0.99 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted water-like geometry to one K(1), one C(3), and one H(6) atom. In the second O site, O(2) is bonded in a distorted water-like geometry to one Na(1), one H(10), and one H(9) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one K(1), one Na(1), one C(2), and one H(6) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one K(1), two equivalent Na(1), and one C(1) atom. In the fifth O site, O(5) is bonded in a distorted water-like geometry to one K(1), one Na(1), one H(3), and one H(7) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one K(1) and one C(3) atom. In the seventh O site, O(7) is bonded in a 1-coordinate geometry to one K(1) and one C(1) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to one K(1), one H(1), one H(2), and one H(5) atom. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one K(1), one Na(1), one C(4), and one H(1) 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 ,8 O. Metal clusters: 4 [K] ,4 [Na]. The MOF has largest included sphere 1.73 A, density 1.83 g/cm3, surface area 1851.23 m2/g, accessible volume 0.05 cm3/g