Fe3As4H3(CO7)3 crystallizes in the trigonal P-3c1 space group. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form FeO6 octahedra that share corners with three equivalent As(1)O4 tetrahedra. The Fe(1)-O(1) bond length is 1.93 Å. The Fe(1)-O(2) bond length is 1.99 Å. The Fe(1)-O(3) bond length is 1.95 Å. The Fe(1)-O(5) bond length is 1.95 Å. The Fe(1)-O(6) bond length is 2.13 Å. The Fe(1)-O(7) bond length is 2.15 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to two equivalent O(6) atoms. Both C(1)-O(6) bond lengths are 1.26 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to two equivalent O(7) atoms. Both C(2)-O(7) bond lengths are 1.25 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-54°. The As(1)-O(1) bond length is 1.66 Å. The As(1)-O(2) bond length is 1.67 Å. The As(1)-O(3) bond length is 1.68 Å. The As(1)-O(4) bond length is 1.72 Å. In the second As site, As(2) is bonded in a trigonal non-coplanar geometry to three equivalent O(5) atoms. All As(2)-O(5) bond lengths are 1.67 Å. H(1) is bonded in a single-bond geometry to one O(4) atom. The H(1)-O(4) bond length is 0.82 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Fe(1) and one C(2) atom. In the second O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the third O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the fourth O site, O(3) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(1) atom. In the fifth O site, O(4) is bonded in a water-like geometry to one As(1) and one H(1) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Fe(1) and one C(1) atom. In the seventh O site, O(5) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(2) atom. Linkers: 6 [O]C(=O)C([O])=O. Metal clusters: 12 [Fe]. The MOF has largest included sphere 6.61 A, density 2.21 g/cm3, surface area 2108.24 m2/g, accessible volume 0.20 cm3/g