MgC5H(NO2)2 crystallizes in the trigonal R-3 space group. Mg(1) is bonded to one O(1), one O(2), one O(3), and two equivalent O(4) atoms to form corner-sharing MgO5 square pyramids. The Mg(1)-O(1) bond length is 2.05 Å. The Mg(1)-O(2) bond length is 2.03 Å. The Mg(1)-O(3) bond length is 2.07 Å. There is one shorter (2.11 Å) and one longer (2.12 Å) Mg(1)-O(4) bond length. There are five inequivalent C sites. In the first C site, C(1) is bonded in a bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.49 Å. The C(1)-O(1) bond length is 1.26 Å. The C(1)-O(2) bond length is 1.26 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(4) atom. The C(2)-C(3) bond length is 1.39 Å. The C(2)-C(4) bond length is 1.41 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 N(2) atom. The C(3)-C(4) bond length is 1.40 Å. The C(3)-N(2) bond length is 1.30 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(2), one C(3), and one N(1) atom. The C(4)-N(1) bond length is 1.42 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one H(1), one O(3), and one O(4) atom. The C(5)-H(1) bond length is 0.93 Å. The C(5)-O(3) bond length is 1.23 Å. The C(5)-O(4) bond length is 1.25 Å. There are two inequivalent N sites. In the first N site, N(1) is bonded in a single-bond geometry to one C(4) atom. In the second N site, N(2) is bonded in a single-bond geometry to one C(3) atom. H(1) 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 bent 120 degrees geometry to one Mg(1) and one C(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one C(5) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to two equivalent Mg(1) and one C(5) atom. Linkers: 9 [N]c1c([N])c(C([O])=O)c([N])c([N])c1C([O])=O. Metal clusters: 3 [C]1O[Mg]O[C]O[Mg]O[C]O[Mg]O[C]O[Mg]O[C]O[Mg]O[C]O[Mg]O1.[O]C=O.[O]C=O.[O]C=O.[O]C=O.[O]C=O.[O]C=O. RCSR code: pcu. The MOF has largest included sphere 5.60 A, density 0.90 g/cm3, surface area 3973.99 m2/g, accessible volume 0.70 cm3/g