ErCoC12H7(NO2)4 crystallizes in the monoclinic C2/c space group. Er(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(5), one O(7), and two equivalent O(6) atoms. The Er(1)-O(1) bond length is 2.26 Å. The Er(1)-O(3) bond length is 2.23 Å. The Er(1)-O(5) bond length is 2.41 Å. The Er(1)-O(7) bond length is 2.19 Å. There is one shorter (2.36 Å) and one longer (2.50 Å) Er(1)-O(6) bond length. Co(1) is bonded in an octahedral geometry to one N(1), one N(2), one N(4), one O(2), one O(4), and one O(8) atom. The Co(1)-N(1) bond length is 2.06 Å. The Co(1)-N(2) bond length is 2.05 Å. The Co(1)-N(4) bond length is 2.11 Å. The Co(1)-O(2) bond length is 2.16 Å. The Co(1)-O(4) bond length is 2.14 Å. The Co(1)-O(8) bond length is 2.10 Å. There are twelve inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(2) atom. The C(1)-O(1) bond length is 1.26 Å. The C(1)-O(2) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted single-bond geometry to one C(3) and one N(1) atom. The C(2)-C(3) bond length is 1.36 Å. The C(2)-N(1) bond length is 1.35 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2), one C(4), and one N(2) atom. The C(3)-C(4) bond length is 1.46 Å. The C(3)-N(2) bond length is 1.36 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(3), and one O(4) atom. The C(4)-O(3) bond length is 1.27 Å. The C(4)-O(4) bond length is 1.25 Å. In the fifth C site, C(5) is bonded in a distorted trigonal planar geometry to one C(6), one N(1), and one N(2) atom. The C(5)-C(6) bond length is 1.48 Å. The C(5)-N(1) bond length is 1.33 Å. The C(5)-N(2) bond length is 1.33 Å. In the sixth C site, C(6) is bonded in a trigonal non-coplanar geometry to one C(5) and three equivalent H(2,3,4) atoms. All C(6)-H(2,3,4) bond lengths are 0.96 Å. In the seventh C site, C(7) is bonded in a bent 120 degrees geometry to one C(8), one O(5), and one O(6) atom. The C(7)-C(8) bond length is 1.47 Å. The C(7)-O(5) bond length is 1.25 Å. The C(7)-O(6) bond length is 1.25 Å. In the eighth C site, C(8) is bonded in a distorted single-bond geometry to one C(7), one C(9), and one N(3) atom. The C(8)-C(9) bond length is 1.35 Å. The C(8)-N(3) bond length is 1.37 Å. In the ninth C site, C(9) is bonded in a distorted single-bond geometry to one C(8) and one N(4) atom. The C(9)-N(4) bond length is 1.37 Å. In the tenth C site, C(10) is bonded in a distorted bent 120 degrees geometry to one O(7) and one O(8) atom. The C(10)-O(7) bond length is 1.25 Å. The C(10)-O(8) bond length is 1.24 Å. In the eleventh C site, C(11) is bonded in a distorted trigonal planar geometry to one C(12), one N(3), and one N(4) atom. The C(11)-C(12) bond length is 1.49 Å. The C(11)-N(3) bond length is 1.33 Å. The C(11)-N(4) bond length is 1.32 Å. In the twelfth C site, C(12) is bonded in a trigonal non-coplanar geometry to one C(11) and three equivalent H(5,6,7) atoms. All C(12)-H(5,6,7) bond lengths are 0.96 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Co(1), one C(2), and one C(5) atom. In the second N site, N(2) is bonded in a distorted trigonal planar geometry to one Co(1), one C(3), and one C(5) atom. In the third N site, N(3) is bonded in a trigonal planar geometry to one C(11), one C(8), and one H(1) atom. The N(3)-H(1) bond length is 0.86 Å. In the fourth N site, N(4) is bonded in a distorted trigonal planar geometry to one Co(1), one C(11), and one C(9) atom. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one N(3) atom. In the second H site, H(2,3,4) is bonded in a single-bond geometry to one C(6) atom. In the third H site, H(5,6,7) is bonded in a single-bond geometry to one C(12) atom. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a bent 120 degrees geometry to one Co(1) and one C(4) atom. In the second O site, O(5) is bonded in a distorted single-bond geometry to one Er(1) and one C(7) atom. In the third O site, O(6) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(7) atom. In the fourth O site, O(7) is bonded in a bent 150 degrees geometry to one Er(1) and one C(10) atom. In the fifth O site, O(8) is bonded in a bent 120 degrees geometry to one Co(1) and one C(10) atom. In the sixth O site, O(1) is bonded in a bent 150 degrees geometry to one Er(1) and one C(1) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Co(1) and one C(1) atom. In the eighth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one C(4) atom. Linkers: 8 Cc1nc(C([O])=O)c(C([O])=O)[nH]1 ,8 CC1=NC(C([O])=O)=C(C([O])=O)[N]1. Metal clusters: 8 [Er] ,8 [Co]. The MOF has largest included sphere 5.75 A, density 2.01 g/cm3, surface area 2704.94 m2/g, accessible volume 0.20 cm3/g