ErC5PNH7O7 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded in a 6-coordinate geometry to one N(1), one O(1), one O(2), one O(4), one O(6), and one O(7) atom. The Er(1)-N(1) bond length is 2.66 Å. The Er(1)-O(1) bond length is 2.31 Å. The Er(1)-O(2) bond length is 2.35 Å. The Er(1)-O(4) bond length is 2.38 Å. The Er(1)-O(6) bond length is 2.27 Å. The Er(1)-O(7) bond length is 2.30 Å. There are five inequivalent C sites. In the first C site, C(1) is bonded in a distorted tetrahedral geometry to one P(1); one N(1); and two equivalent H(1,2) atoms. The C(1)-P(1) bond length is 1.83 Å. The C(1)-N(1) bond length is 1.51 Å. Both C(1)-H(1,2) bond lengths are 0.97 Å. In the second C site, C(2) is bonded in a 3-coordinate geometry to one N(1) and two equivalent H(3,4) atoms. The C(2)-N(1) bond length is 1.49 Å. Both C(2)-H(3,4) bond lengths are 0.97 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(2) atom. The C(3)-O(1) bond length is 1.29 Å. The C(3)-O(2) bond length is 1.26 Å. In the fourth C site, C(4) is bonded in a 3-coordinate geometry to one N(1) and two equivalent H(5,6) atoms. The C(4)-N(1) bond length is 1.48 Å. Both C(4)-H(5,6) bond lengths are 0.97 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one O(3) and one O(4) atom. The C(5)-O(3) bond length is 1.29 Å. The C(5)-O(4) bond length is 1.27 Å. P(1) is bonded in a distorted tetrahedral geometry to one C(1), one O(5), one O(6), and one O(7) atom. The P(1)-O(5) bond length is 1.57 Å. The P(1)-O(6) bond length is 1.51 Å. The P(1)-O(7) bond length is 1.50 Å. N(1) is bonded in a distorted trigonal non-coplanar geometry to one Er(1), one C(1), one C(2), and one C(4) atom. There are four inequivalent H sites. In the first H site, H(1,2) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(3,4) is bonded in a single-bond geometry to one C(2) atom. In the third H site, H(5,6) is bonded in a single-bond geometry to one C(4) atom. In the fourth H site, H(7) is bonded in a single-bond geometry to one O(5) atom. The H(7)-O(5) bond length is 0.82 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Er(1) and one C(3) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one C(3) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one C(5) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(5) atom. In the fifth O site, O(5) is bonded in a water-like geometry to one P(1) and one H(7) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Er(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one P(1) atom. Linkers: 4 [O]C(=O)CN(CC([O])=O)CP([O])(=O)O. Metal clusters: 4 [Er]. RCSR code: srs. The MOF has largest included sphere 4.14 A, density 2.03 g/cm3, surface area 2685.55 m2/g, accessible volume 0.16 cm3/g