CaC6N2H8O7 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 8-coordinate geometry to one N(1), one N(2), one O(1), one O(5), one O(6), one O(7), and two equivalent O(3) atoms. The Ca(1)-N(1) bond length is 2.59 Å. The Ca(1)-N(2) bond length is 2.57 Å. The Ca(1)-O(1) bond length is 2.42 Å. The Ca(1)-O(5) bond length is 2.43 Å. The Ca(1)-O(6) bond length is 2.42 Å. The Ca(1)-O(7) bond length is 2.60 Å. There is one shorter (2.52 Å) and one longer (2.53 Å) Ca(1)-O(3) bond length. There are six inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one N(1), one N(2), and one H(1) atom. The C(1)-N(1) bond length is 1.34 Å. The C(1)-N(2) bond length is 1.34 Å. The C(1)-H(1) bond length is 1.09 Å. In the second C site, C(2) is bonded in a distorted trigonal planar geometry to one C(3), one C(6), and one N(2) atom. The C(2)-C(3) bond length is 1.39 Å. The C(2)-C(6) bond length is 1.51 Å. The C(2)-N(2) bond length is 1.34 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2), one C(4), and one H(2) atom. The C(3)-C(4) bond length is 1.39 Å. The C(3)-H(2) bond length is 1.08 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(3), one C(5), and one N(1) atom. The C(4)-C(5) bond length is 1.52 Å. The C(4)-N(1) bond length is 1.34 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one C(4), one O(1), and one O(2) atom. The C(5)-O(1) bond length is 1.26 Å. The C(5)-O(2) bond length is 1.27 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(3), and one O(4) atom. The C(6)-O(3) bond length is 1.28 Å. The C(6)-O(4) bond length is 1.27 Å. There are two inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one C(1), and one C(4) atom. In the second N site, N(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one C(1), and one C(2) atom. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(3) 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 1.00 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(2) and one O(5) atom. The H(4)-O(2) bond length is 1.71 Å. The H(4)-O(5) bond length is 0.99 Å. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(6) atom. The H(5)-O(6) bond length is 0.99 Å. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(6) atom. The H(6)-O(6) bond length is 0.97 Å. In the seventh H site, H(7) is bonded in a single-bond geometry to one O(7) atom. The H(7)-O(7) bond length is 0.99 Å. In the eighth H site, H(8) is bonded in a single-bond geometry to one O(2) and one O(7) atom. The H(8)-O(2) bond length is 1.69 Å. The H(8)-O(7) bond length is 1.00 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one C(5) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one C(5), one H(4), and one H(8) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Ca(1) and one C(6) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one C(6) atom. In the fifth 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 sixth O site, O(6) is bonded in a distorted water-like geometry to one Ca(1), one H(5), and one H(6) atom. In the seventh O site, O(7) is bonded in a water-like geometry to one Ca(1), one H(7), and one H(8) atom. Linkers: 4 [O]C(=O)c1cc(C([O])=O)ncn1. Metal clusters: 4 [Ca]. The MOF has largest included sphere 2.15 A, density 1.83 g/cm3, surface area 3305.25 m2/g, accessible volume 0.08 cm3/g