CaC7H4O5 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(5), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Ca(1)-O(1) bond length is 2.42 Å. The Ca(1)-O(5) bond length is 2.37 Å. There is one shorter (2.36 Å) and one longer (2.96 Å) Ca(1)-O(2) bond length. There is one shorter (2.35 Å) and one longer (2.57 Å) Ca(1)-O(3) bond length. There is one shorter (2.41 Å) and one longer (2.54 Å) Ca(1)-O(4) bond length. There are seven inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one C(1), one C(2), and one C(5) atom. The C(1)-C(1) bond length is 1.45 Å. The C(1)-C(2) bond length is 1.43 Å. The C(1)-C(5) bond length is 1.43 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one C(1), one C(3), and one C(6) atom. The C(2)-C(3) bond length is 1.38 Å. The C(2)-C(6) bond length is 1.49 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2) and one H(1) atom. The C(3)-H(1) bond length is 1.09 Å. In the fourth C site, C(4) is bonded in a distorted single-bond geometry to one C(5) and one H(2) atom. The C(4)-C(5) bond length is 1.39 Å. The C(4)-H(2) bond length is 1.09 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one C(1), one C(4), and one C(7) atom. The C(5)-C(7) bond length is 1.51 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(6)-O(1) bond length is 1.27 Å. The C(6)-O(2) bond length is 1.28 Å. In the seventh C site, C(7) is bonded in a distorted bent 120 degrees geometry to one C(5), one O(3), and one O(4) atom. The C(7)-O(3) bond length is 1.27 Å. The C(7)-O(4) bond length is 1.28 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(3) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(4) atom. 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 O(1) and one O(5) atom. The H(4)-O(1) bond length is 1.69 Å. The H(4)-O(5) bond length is 0.99 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded in a distorted water-like geometry to one Ca(1), one H(3), and one H(4) atom. In the second O site, O(1) is bonded in a distorted single-bond geometry to one Ca(1), one C(6), and one H(4) atom. In the third O site, O(2) is bonded in a 1-coordinate geometry to two equivalent Ca(1) and one C(6) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(7) atom. In the fifth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Ca(1) and one C(7) atom. Linkers: 1 [O]C(=O)c1ccc(C([O])=O)c2c(C([O])=O)ccc(C([O])=O)c12. Metal clusters: 2 [Ca]. RCSR code: flu. The MOF has largest included sphere 2.09 A, density 1.95 g/cm3, surface area 2706.95 m2/g, accessible volume 0.06 cm3/g