Er2C21H9(NO4)3 crystallizes in the hexagonal P6_3cm space group. Er(1) is bonded in a 9-coordinate geometry to three equivalent O(2) and six equivalent O(1) atoms. All Er(1)-O(2) bond lengths are 2.32 Å. There are three shorter (2.35 Å) and three longer (2.54 Å) Er(1)-O(1) bond lengths. There are four inequivalent C sites. In the first 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(1) bond length is 1.40 Å. The C(2)-C(3) bond length is 1.39 Å. The C(2)-C(4) bond length is 1.48 Å. In the second C site, C(3) is bonded in a distorted single-bond geometry to two equivalent C(2) and one H(2) atom. The C(3)-H(2) bond length is 1.09 Å. In the third 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 1.30 Å. The C(4)-O(2) bond length is 1.27 Å. In the fourth C site, C(1) is bonded in a distorted trigonal planar geometry to one C(2), one N(1), and one H(1) atom. The C(1)-N(1) bond length is 1.34 Å. The C(1)-H(1) bond length is 1.09 Å. N(1) is bonded in a bent 120 degrees geometry to two equivalent C(1) atoms. There are two 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. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(4) atom. In the second O site, O(2) is bonded in a distorted water-like geometry to one Er(1) and one C(4) atom. Linkers: 6 [O]C(=O)c1cncc(C([O])=O)c1. Metal clusters: 4 [Er]. The MOF has largest included sphere 8.60 A, density 1.65 g/cm3, surface area 2500.34 m2/g, accessible volume 0.31 cm3/g