EuC3O5 crystallizes in the orthorhombic Pba2 space group. Eu(1) is bonded in a 8-coordinate geometry to one O(3), one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms. The Eu(1)-O(3) bond length is 2.37 Å. The Eu(1)-O(4) bond length is 2.46 Å. Both Eu(1)-O(1) bond lengths are 2.41 Å. There is one shorter (2.45 Å) and one longer (2.51 Å) Eu(1)-O(2) bond length. There is one shorter (2.39 Å) and one longer (2.57 Å) Eu(1)-O(5) bond length. There are three inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(5) atom. The C(1)-O(1) bond length is 1.39 Å. The C(1)-O(2) bond length is 1.25 Å. The C(1)-O(5) bond length is 1.27 Å. In the second C site, C(2) is bonded in a linear geometry to one C(2) and one C(3) atom. The C(2)-C(2) bond length is 1.21 Å. The C(2)-C(3) bond length is 1.44 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(3), and one O(4) atom. The C(3)-O(3) bond length is 1.24 Å. The C(3)-O(4) bond length is 1.24 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Eu(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Eu(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Eu(1) and one C(3) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Eu(1) and one C(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Eu(1) and one C(1) atom. Linkers: 2 [O]C(=O)C#CC([O])=O. Metal clusters: 4 [Eu]. The MOF has largest included sphere 3.90 A, density 2.70 g/cm3, surface area 1587.56 m2/g, accessible volume 0.11 cm3/g