CaC7NH3O4 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 7-coordinate geometry to one N(1), one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms. The Ca(1)-N(1) bond length is 2.56 Å. The Ca(1)-O(2) bond length is 2.46 Å. The Ca(1)-O(3) bond length is 2.56 Å. There is one shorter (2.45 Å) and one longer (2.49 Å) Ca(1)-O(1) bond length. There is one shorter (2.36 Å) and one longer (2.50 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(4), one C(5), and one C(6) atom. The C(1)-C(4) bond length is 1.38 Å. The C(1)-C(5) bond length is 1.38 Å. The C(1)-C(6) bond length is 1.51 Å. In the second C site, C(2) is bonded in a distorted trigonal planar geometry to one C(3), one C(7), and one N(1) atom. The C(2)-C(3) bond length is 1.38 Å. The C(2)-C(7) bond length is 1.52 Å. The C(2)-N(1) bond length is 1.33 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 0.93 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(1), one N(1), and one H(2) atom. The C(4)-N(1) bond length is 1.34 Å. The C(4)-H(2) bond length is 0.93 Å. In the fifth C site, C(5) is bonded in a distorted single-bond geometry to one C(1) and one H(3) atom. The C(5)-H(3) bond length is 0.93 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(1), one O(3), and one O(4) atom. The C(6)-O(3) bond length is 1.24 Å. The C(6)-O(4) bond length is 1.25 Å. In the seventh C site, C(7) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(7)-O(1) bond length is 1.27 Å. The C(7)-O(2) bond length is 1.24 Å. N(1) is bonded in a trigonal planar geometry to one Ca(1), one C(2), and one C(4) atom. There are three 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 C(5) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one C(7) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ca(1) and one C(7) atom. In the third O site, O(3) is bonded in a distorted L-shaped geometry to one Ca(1) and one C(6) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to two equivalent Ca(1) and one C(6) atom. Linkers: 4 [O]C(=O)c1ccc(C([O])=O)nc1. Metal clusters: 4 [Ca]. The MOF has largest included sphere 5.69 A, density 1.21 g/cm3, surface area 3337.32 m2/g, accessible volume 0.34 cm3/g