EuC4N3O4 crystallizes in the orthorhombic P2_12_12_1 space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 6-coordinate geometry to one N(3), one N(4), one O(2), one O(3), one O(4), and one O(5) atom. The Eu(1)-N(3) bond length is 2.52 Å. The Eu(1)-N(4) bond length is 2.55 Å. The Eu(1)-O(2) bond length is 2.32 Å. The Eu(1)-O(3) bond length is 2.47 Å. The Eu(1)-O(4) bond length is 2.35 Å. The Eu(1)-O(5) bond length is 2.43 Å. In the second Eu site, Eu(2) is bonded in a distorted pentagonal pyramidal geometry to one N(1), one N(6), one O(1), one O(6), one O(7), and one O(8) atom. The Eu(2)-N(1) bond length is 2.47 Å. The Eu(2)-N(6) bond length is 2.56 Å. The Eu(2)-O(1) bond length is 2.47 Å. The Eu(2)-O(6) bond length is 2.30 Å. The Eu(2)-O(7) bond length is 2.48 Å. The Eu(2)-O(8) bond length is 2.32 Å. There are eight inequivalent C sites. In the first C site, C(1) is bonded in a 3-coordinate geometry to one C(2), one C(3), and one N(1) atom. The C(1)-C(2) bond length is 1.33 Å. The C(1)-C(3) bond length is 1.50 Å. The C(1)-N(1) bond length is 1.38 Å. In the second C site, C(2) is bonded in a 3-coordinate geometry to one C(1), one C(4), and one N(3) atom. The C(2)-C(4) bond length is 1.50 Å. The C(2)-N(3) bond length is 1.41 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one C(1), one O(1), and one O(2) atom. The C(3)-O(1) bond length is 1.27 Å. The C(3)-O(2) bond length is 1.24 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(3), and one O(4) atom. The C(4)-O(3) bond length is 1.24 Å. The C(4)-O(4) bond length is 1.27 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one C(8), one O(7), and one O(8) atom. The C(5)-C(8) bond length is 1.43 Å. The C(5)-O(7) bond length is 1.32 Å. The C(5)-O(8) bond length is 1.23 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(7), one O(5), and one O(6) atom. The C(6)-C(7) bond length is 1.48 Å. The C(6)-O(5) bond length is 1.25 Å. The C(6)-O(6) bond length is 1.26 Å. In the seventh C site, C(7) is bonded in a 3-coordinate geometry to one C(6), one C(8), and one N(4) atom. The C(7)-C(8) bond length is 1.37 Å. The C(7)-N(4) bond length is 1.39 Å. In the eighth C site, C(8) is bonded in a 3-coordinate geometry to one C(5), one C(7), and one N(6) atom. The C(8)-N(6) bond length is 1.33 Å. There are six inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Eu(2), one C(1), and one N(2) atom. The N(1)-N(2) bond length is 1.39 Å. In the second N site, N(2) is bonded in a water-like geometry to one N(1) and one N(3) atom. The N(2)-N(3) bond length is 1.32 Å. In the third N site, N(3) is bonded in a distorted single-bond geometry to one Eu(1), one C(2), and one N(2) atom. In the fourth N site, N(4) is bonded in a distorted trigonal planar geometry to one Eu(1), one C(7), and one N(5) atom. The N(4)-N(5) bond length is 1.30 Å. In the fifth N site, N(5) is bonded in a water-like geometry to one N(4) and one N(6) atom. The N(5)-N(6) bond length is 1.34 Å. In the sixth N site, N(6) is bonded in a 1-coordinate geometry to one Eu(2), one C(8), and one N(5) atom. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Eu(2) and one C(3) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Eu(1) and one C(3) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Eu(1) and one C(4) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Eu(1) and one C(4) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Eu(1) and one C(6) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Eu(2) and one C(6) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Eu(2) and one C(5) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Eu(2) and one C(5) atom. Linkers: 2 [O]C(=O)[C]1N=NN=C1C([O])=O ,1 [O]C(=O)C1=C(C([O])=O)N=N[N]1 ,4 [O]C(=O)C1=N[N]N=C1C([O])=O. Metal clusters: 8 [Eu]. The MOF has largest included sphere 5.11 A, density 1.88 g/cm3, surface area 2296.85 m2/g, accessible volume 0.25 cm3/g