CaC4N11H3O crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 7-coordinate geometry to one N(1), one N(2), one N(4), one N(6), one N(8), one N(9), and one O(1) atom. The Ca(1)-N(1) bond length is 2.52 Å. The Ca(1)-N(2) bond length is 2.57 Å. The Ca(1)-N(4) bond length is 2.59 Å. The Ca(1)-N(6) bond length is 2.49 Å. The Ca(1)-N(8) bond length is 2.51 Å. The Ca(1)-N(9) bond length is 2.66 Å. The Ca(1)-O(1) bond length is 2.36 Å. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted water-like geometry to one C(2), one N(1), and one N(8) atom. The C(1)-C(2) bond length is 1.45 Å. The C(1)-N(1) bond length is 1.35 Å. The C(1)-N(8) bond length is 1.35 Å. In the second C site, C(2) is bonded in a distorted single-bond geometry to one C(1) and one N(2) atom. The C(2)-N(2) bond length is 1.35 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(4) and one N(5) atom. The C(3)-C(4) bond length is 1.45 Å. The C(3)-N(5) bond length is 1.35 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(3), one N(6), and one N(9) atom. The C(4)-N(6) bond length is 1.34 Å. The C(4)-N(9) bond length is 1.35 Å. There are eleven inequivalent N sites. In the first N site, N(1) is bonded in a 3-coordinate geometry to one Ca(1), one C(1), and one N(10) atom. The N(1)-N(10) bond length is 1.35 Å. In the second N site, N(2) is bonded in a 3-coordinate geometry to one Ca(1), one C(2), and one N(7) atom. The N(2)-N(7) bond length is 1.32 Å. In the third N site, N(3) is bonded in a water-like geometry to one N(11) and one N(9) atom. The N(3)-N(11) bond length is 1.32 Å. The N(3)-N(9) bond length is 1.35 Å. In the fourth N site, N(4) is bonded in a trigonal planar geometry to one Ca(1), one N(10), and one N(8) atom. The N(4)-N(10) bond length is 1.32 Å. The N(4)-N(8) bond length is 1.34 Å. In the fifth N site, N(5) is bonded in a distorted water-like geometry to one C(3) and one N(7) atom. The N(5)-N(7) bond length is 1.32 Å. In the sixth N site, N(6) is bonded in a 3-coordinate geometry to one Ca(1), one C(4), and one N(11) atom. The N(6)-N(11) bond length is 1.35 Å. In the seventh N site, N(7) is bonded in a distorted single-bond geometry to one N(2), one N(5), and one H(3) atom. The N(7)-H(3) bond length is 1.04 Å. In the eighth N site, N(8) is bonded in a 3-coordinate geometry to one Ca(1), one C(1), and one N(4) atom. In the ninth N site, N(9) is bonded in a distorted single-bond geometry to one Ca(1), one C(4), and one N(3) atom. In the tenth N site, N(10) is bonded in a water-like geometry to one N(1) and one N(4) atom. In the eleventh N site, N(11) is bonded in a distorted water-like geometry to one N(3) and one N(6) atom. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(1) atom. The H(1)-O(1) bond length is 0.99 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(1) atom. The H(2)-O(1) bond length is 0.98 Å. In the third H site, H(3) is bonded in a single-bond geometry to one N(7) atom. O(1) is bonded in a distorted water-like geometry to one Ca(1), one H(1), and one H(2) atom. Linkers: 4 [N]1N=NN=C1c1n[nH]nc1C1=NN=N[N]1. Metal clusters: 2 O.O.[N][N][Ca].[N][N][Ca]. The MOF has largest included sphere 1.62 A, density 2.06 g/cm3, surface area 3078.21 m2/g, accessible volume 0.08 cm3/g