Eu(CO2)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 8-coordinate geometry to one O(13), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Eu(1)-O(13) bond length is 2.53 Å. The Eu(1)-O(3) bond length is 2.49 Å. The Eu(1)-O(4) bond length is 2.40 Å. The Eu(1)-O(5) bond length is 2.46 Å. The Eu(1)-O(6) bond length is 2.47 Å. The Eu(1)-O(7) bond length is 2.46 Å. The Eu(1)-O(8) bond length is 2.47 Å. The Eu(1)-O(9) bond length is 2.45 Å. In the second Eu site, Eu(2) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(11), one O(12), one O(14), one O(15), one O(16), and one O(2) atom. The Eu(2)-O(1) bond length is 2.45 Å. The Eu(2)-O(10) bond length is 2.46 Å. The Eu(2)-O(11) bond length is 2.45 Å. The Eu(2)-O(12) bond length is 2.41 Å. The Eu(2)-O(14) bond length is 2.47 Å. The Eu(2)-O(15) bond length is 2.51 Å. The Eu(2)-O(16) bond length is 2.45 Å. The Eu(2)-O(2) bond length is 2.48 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 O(2) and one O(3) atom. The C(1)-O(2) bond length is 1.26 Å. The C(1)-O(3) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(4) atom. The C(2)-O(1) bond length is 1.25 Å. The C(2)-O(4) bond length is 1.24 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(14) and one O(8) atom. The C(3)-O(14) bond length is 1.26 Å. The C(3)-O(8) bond length is 1.25 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one O(12) and one O(5) atom. The C(4)-O(12) bond length is 1.26 Å. The C(4)-O(5) bond length is 1.24 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one O(13) and one O(9) atom. The C(5)-O(13) bond length is 1.24 Å. The C(5)-O(9) bond length is 1.26 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one O(11) and one O(7) atom. The C(6)-O(11) bond length is 1.25 Å. The C(6)-O(7) bond length is 1.27 Å. In the seventh C site, C(7) is bonded in a distorted bent 120 degrees geometry to one O(15) and one O(6) atom. The C(7)-O(15) 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 bent 120 degrees geometry to one O(10) and one O(16) atom. The C(8)-O(10) bond length is 1.25 Å. The C(8)-O(16) bond length is 1.26 Å. There are sixteen 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(2) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Eu(2) and one C(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Eu(1) and one C(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Eu(1) and one C(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Eu(1) and one C(4) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Eu(1) and one C(7) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Eu(1) and one C(6) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Eu(1) and one C(3) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Eu(1) and one C(5) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Eu(2) and one C(8) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Eu(2) and one C(6) atom. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Eu(2) and one C(4) atom. In the thirteenth O site, O(13) is bonded in a distorted bent 120 degrees geometry to one Eu(1) and one C(5) atom. In the fourteenth O site, O(14) is bonded in a bent 120 degrees geometry to one Eu(2) and one C(3) atom. In the fifteenth O site, O(15) is bonded in a distorted bent 120 degrees geometry to one Eu(2) and one C(7) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 120 degrees geometry to one Eu(2) and one C(8) atom. Linkers: 14 [O]C(=O)C([O])=O. Metal clusters: 8 [Eu]. The MOF has largest included sphere 5.53 A, density 1.71 g/cm3, surface area 2336.72 m2/g, accessible volume 0.29 cm3/g