Eu5(C4O7)3 crystallizes in the monoclinic C2/m space group. There are five inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 10-coordinate geometry to one O(13), one O(14), two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Eu(1)-O(13) bond length is 2.86 Å. The Eu(1)-O(14) bond length is 2.65 Å. Both Eu(1)-O(1) bond lengths are 2.51 Å. Both Eu(1)-O(2) bond lengths are 2.57 Å. Both Eu(1)-O(3) bond lengths are 2.54 Å. Both Eu(1)-O(4) bond lengths are 2.45 Å. In the second Eu site, Eu(2) is bonded in a 8-coordinate geometry to one O(14), one O(9), two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms. The Eu(2)-O(14) bond length is 2.67 Å. The Eu(2)-O(9) bond length is 2.30 Å. Both Eu(2)-O(1) bond lengths are 2.46 Å. Both Eu(2)-O(2) bond lengths are 2.42 Å. Both Eu(2)-O(7) bond lengths are 2.68 Å. In the third Eu site, Eu(3) is bonded in a 6-coordinate geometry to one O(10), one O(14), two equivalent O(1), and two equivalent O(2) atoms. The Eu(3)-O(10) bond length is 2.60 Å. The Eu(3)-O(14) bond length is 2.62 Å. Both Eu(3)-O(1) bond lengths are 2.41 Å. Both Eu(3)-O(2) bond lengths are 2.48 Å. In the fourth Eu site, Eu(4) is bonded in a 8-coordinate geometry to one O(11), one O(13), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. The Eu(4)-O(11) bond length is 2.45 Å. The Eu(4)-O(13) bond length is 2.75 Å. Both Eu(4)-O(3) bond lengths are 2.43 Å. Both Eu(4)-O(4) bond lengths are 2.61 Å. Both Eu(4)-O(5) bond lengths are 2.41 Å. In the fifth Eu site, Eu(5) is bonded in a 7-coordinate geometry to one O(13), two equivalent O(3), two equivalent O(4), and two equivalent O(8) atoms. The Eu(5)-O(13) bond length is 2.79 Å. Both Eu(5)-O(3) bond lengths are 2.46 Å. Both Eu(5)-O(4) bond lengths are 2.51 Å. Both Eu(5)-O(8) bond lengths are 2.52 Å. There are eight 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(5), and one O(6) atom. The C(1)-C(2) bond length is 1.42 Å. The C(1)-O(5) bond length is 1.28 Å. The C(1)-O(6) bond length is 1.19 Å. In the second C site, C(2) is bonded in a bent 120 degrees geometry to one C(1) and one C(3) atom. The C(2)-C(3) bond length is 1.45 Å. In the third C site, C(3) is bonded in a bent 120 degrees geometry to one C(2) and one C(4) atom. The C(3)-C(4) bond length is 1.55 Å. In the fourth C site, C(4) is bonded in a distorted trigonal planar geometry to one C(3), one O(7), and one O(8) atom. The C(4)-O(7) bond length is 1.41 Å. The C(4)-O(8) bond length is 1.36 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one C(8), one O(10), and one O(9) atom. The C(5)-C(8) bond length is 1.47 Å. The C(5)-O(10) bond length is 1.32 Å. The C(5)-O(9) bond length is 1.28 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(7), one O(11), and one O(12) atom. The C(6)-C(7) bond length is 1.37 Å. The C(6)-O(11) bond length is 1.30 Å. The C(6)-O(12) bond length is 1.27 Å. In the seventh C site, C(7) is bonded in a bent 120 degrees geometry to one C(6) and one C(8) atom. The C(7)-C(8) bond length is 1.31 Å. In the eighth C site, C(8) is bonded in a bent 120 degrees geometry to one C(5) and one C(7) atom. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Eu(1), one Eu(2), and one Eu(3) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Eu(1), one Eu(2), and one Eu(3) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Eu(1), one Eu(4), and one Eu(5) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Eu(1), one Eu(4), and one Eu(5) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Eu(4) and one C(1) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one C(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Eu(2) and one C(4) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Eu(5) and one C(4) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Eu(2) and one C(5) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Eu(3) and one C(5) atom. In the eleventh O site, O(11) is bonded in a linear geometry to one Eu(4) and one C(6) atom. In the twelfth O site, O(12) is bonded in a single-bond geometry to one C(6) atom. In the thirteenth O site, O(13) is bonded to two equivalent Eu(1), two equivalent Eu(4), and two equivalent Eu(5) atoms to form corner-sharing OEu6 octahedra. The corner-sharing octahedra are not tilted. In the fourteenth O site, O(14) is bonded to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Eu(3) atoms to form corner-sharing OEu6 octahedra. The corner-sharing octahedra are not tilted. Linkers: 4 [O]C(=O)/[C]=[C]\C([O])=O ,8 [O]C(=O)[C][C]C([O])=O. Metal clusters: 20 [Eu]. The MOF has largest included sphere 5.22 A, density 2.49 g/cm3, surface area 1760.61 m2/g, accessible volume 0.17 cm3/g