ErCrC6NH4O6 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded in a 8-coordinate geometry to one N(1), one O(1), one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms. The Er(1)-N(1) bond length is 2.56 Å. The Er(1)-O(1) bond length is 2.26 Å. The Er(1)-O(2) bond length is 2.30 Å. The Er(1)-O(5) bond length is 2.25 Å. There is one shorter (2.31 Å) and one longer (2.53 Å) Er(1)-O(3) bond length. There is one shorter (2.33 Å) and one longer (2.36 Å) Er(1)-O(4) bond length. Cr(1) is bonded in a tetrahedral geometry to one O(3), one O(4), one O(5), and one O(6) atom. The Cr(1)-O(3) bond length is 1.67 Å. The Cr(1)-O(4) bond length is 1.71 Å. The Cr(1)-O(5) bond length is 1.65 Å. The Cr(1)-O(6) bond length is 1.60 Å. There are six inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.50 Å. The C(1)-O(1) bond length is 1.27 Å. The C(1)-O(2) bond length is 1.27 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(5) atom. The C(2)-C(3) bond length is 1.40 Å. The C(2)-C(5) bond length is 1.40 Å. In the third C site, C(3) is bonded in a distorted trigonal planar geometry to one C(2), one C(4), and one H(1) atom. The C(3)-C(4) bond length is 1.39 Å. The C(3)-H(1) bond length is 1.09 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(3), one N(1), and one H(2) atom. The C(4)-N(1) bond length is 1.35 Å. The C(4)-H(2) bond length is 1.09 Å. In the fifth C site, C(5) is bonded in a distorted trigonal planar geometry to one C(2), one C(6), and one H(3) atom. The C(5)-C(6) bond length is 1.39 Å. The C(5)-H(3) bond length is 1.09 Å. In the sixth C site, C(6) is bonded in a distorted trigonal planar geometry to one C(5), one N(1), and one H(4) atom. The C(6)-N(1) bond length is 1.35 Å. The C(6)-H(4) bond length is 1.09 Å. N(1) is bonded in a distorted bent 120 degrees geometry to one Er(1), one C(4), and one C(6) atom. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(3) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(4) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(5) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(6) atom. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one Cr(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Er(1) and one Cr(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Er(1) and one Cr(1) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one Cr(1) atom. Linkers: 4 [O]C(=O)c1ccncc1. Metal clusters: 4 [Er] ,4 [Cr]. The MOF has largest included sphere 1.81 A, density 3.08 g/cm3, surface area 1954.46 m2/g, accessible volume 0.04 cm3/g