Er4P6H3(CO6)3 crystallizes in the cubic I2_13 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form distorted ErO6 octahedra that share corners with six equivalent P(1)CO3 tetrahedra and  a faceface with one Er(2)O6 pentagonal pyramid. All Er(1)-O(1) bond lengths are 2.33 Å. All Er(1)-O(3) bond lengths are 2.15 Å. In the second Er site, Er(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted ErO6 pentagonal pyramids that share corners with six equivalent P(1)CO3 tetrahedra and  a faceface with one Er(1)O6 octahedra. All Er(2)-O(1) bond lengths are 2.34 Å. All Er(2)-O(2) bond lengths are 2.17 Å. C(1) is bonded in a trigonal planar geometry to two equivalent P(1) and one H(1) atom. Both C(1)-P(1) bond lengths are 1.77 Å. The C(1)-H(1) bond length is 1.09 Å. P(1) is bonded to one C(1), one O(1), one O(2), and one O(3) atom to form PCO3 tetrahedra that share corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Er(2)O6 pentagonal pyramids, and  a cornercorner with one P(1)CO3 tetrahedra. The corner-sharing octahedral tilt angles range from 32-44°. The P(1)-O(1) bond length is 1.56 Å. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.52 Å. H(1) is bonded in a single-bond geometry to one C(1) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Er(1), one Er(2), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one P(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Er(1) and one P(1) atom. Linkers: 6 [O]P([O])(=O)[CH]P([O])([O])=O. Metal clusters: 8 [Er]. The MOF has largest included sphere 4.29 A, density 3.21 g/cm3, surface area 1513.11 m2/g, accessible volume 0.10 cm3/g