CaC7NH5O5 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded to one O(2), one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form a mixture of distorted edge and corner-sharing CaO7 pentagonal bipyramids. The Ca(1)-O(2) bond length is 2.53 Å. The Ca(1)-O(4) bond length is 2.31 Å. The Ca(1)-O(5) bond length is 2.36 Å. There is one shorter (2.39 Å) and one longer (2.51 Å) Ca(1)-O(1) bond length. There is one shorter (2.40 Å) and one longer (2.42 Å) Ca(1)-O(3) bond length. There are seven inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(3), and one O(4) atom. The C(1)-C(3) bond length is 1.51 Å. The C(1)-O(3) bond length is 1.28 Å. The C(1)-O(4) bond length is 1.25 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one C(3), one C(4), and one C(5) atom. The C(2)-C(3) bond length is 1.41 Å. The C(2)-C(4) bond length is 1.50 Å. The C(2)-C(5) bond length is 1.40 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one C(1), one C(2), and one C(7) atom. The C(3)-C(7) bond length is 1.40 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(4)-O(1) bond length is 1.28 Å. The C(4)-O(2) bond length is 1.27 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one C(2), one N(1), and one H(1) atom. The C(5)-N(1) bond length is 1.34 Å. The C(5)-H(1) bond length is 1.09 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(7), one N(1), and one H(2) atom. The C(6)-C(7) bond length is 1.39 Å. The C(6)-N(1) bond length is 1.35 Å. The C(6)-H(2) bond length is 1.09 Å. In the seventh C site, C(7) is bonded in a distorted trigonal planar geometry to one C(3), one C(6), and one H(3) atom. The C(7)-H(3) bond length is 1.09 Å. N(1) is bonded in a distorted trigonal planar geometry to one C(5), one C(6), and one H(5) atom. The N(1)-H(5) bond length is 1.73 Å. There are five inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(5) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(6) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(7) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(5) atom. The H(4)-O(5) bond length is 0.99 Å. In the fifth H site, H(5) is bonded in a distorted single-bond geometry to one N(1) and one O(5) atom. The H(5)-O(5) bond length is 1.01 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(4) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ca(1) and one C(4) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one C(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ca(1) and one C(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one H(4), and one H(5) atom. Linkers: 4 [O]C(=O)c1ccncc1C([O])=O. Metal clusters: 4 [Ca]. The MOF has largest included sphere 2.38 A, density 1.72 g/cm3, surface area 3666.22 m2/g, accessible volume 0.19 cm3/g