ErH4(CO2)4 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 8-coordinate geometry to one O(1), one O(11), one O(12), one O(13), one O(3), one O(5), one O(7), and one O(9) atom. The Er(1)-O(1) bond length is 2.29 Å. The Er(1)-O(11) bond length is 2.28 Å. The Er(1)-O(12) bond length is 2.43 Å. The Er(1)-O(13) bond length is 2.35 Å. The Er(1)-O(3) bond length is 2.43 Å. The Er(1)-O(5) bond length is 2.31 Å. The Er(1)-O(7) bond length is 2.35 Å. The Er(1)-O(9) bond length is 2.37 Å. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(10), one O(14), one O(15), one O(16), one O(2), one O(4), one O(6), and one O(8) atom. The Er(2)-O(10) bond length is 2.42 Å. The Er(2)-O(14) bond length is 2.29 Å. The Er(2)-O(15) bond length is 2.34 Å. The Er(2)-O(16) bond length is 2.45 Å. The Er(2)-O(2) bond length is 2.35 Å. The Er(2)-O(4) bond length is 2.36 Å. The Er(2)-O(6) bond length is 2.42 Å. The Er(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 trigonal planar geometry to one H(1), one O(1), and one O(2) atom. The C(1)-H(1) bond length is 0.93 Å. The C(1)-O(1) bond length is 1.26 Å. The C(1)-O(2) bond length is 1.19 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one H(2), one O(3), and one O(4) atom. The C(2)-H(2) bond length is 0.93 Å. The C(2)-O(3) bond length is 1.16 Å. The C(2)-O(4) bond length is 1.33 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one H(3), one O(5), and one O(6) atom. The C(3)-H(3) bond length is 0.93 Å. The C(3)-O(5) bond length is 1.18 Å. The C(3)-O(6) bond length is 1.14 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one H(4), one O(7), and one O(8) atom. The C(4)-H(4) bond length is 0.93 Å. The C(4)-O(7) bond length is 1.21 Å. The C(4)-O(8) bond length is 1.23 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one H(5), one O(10), and one O(9) atom. The C(5)-H(5) bond length is 0.93 Å. The C(5)-O(10) bond length is 1.16 Å. The C(5)-O(9) bond length is 1.35 Å. In the sixth C site, C(6) is bonded in a trigonal planar geometry to one H(6), one O(11), and one O(12) atom. The C(6)-H(6) bond length is 0.93 Å. The C(6)-O(11) bond length is 1.31 Å. The C(6)-O(12) bond length is 1.18 Å. In the seventh C site, C(7) is bonded in a trigonal planar geometry to one H(7), one O(13), and one O(14) atom. The C(7)-H(7) bond length is 0.93 Å. The C(7)-O(13) bond length is 1.18 Å. The C(7)-O(14) bond length is 1.30 Å. In the eighth C site, C(8) is bonded in a trigonal planar geometry to one H(8), one O(15), and one O(16) atom. The C(8)-H(8) bond length is 0.93 Å. The C(8)-O(15) bond length is 1.29 Å. The C(8)-O(16) bond length is 1.19 Å. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(2) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(3) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(4) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one C(5) atom. In the sixth H site, H(6) is bonded in a single-bond geometry to one C(6) atom. In the seventh H site, H(7) is bonded in a single-bond geometry to one C(7) atom. In the eighth H site, H(8) is bonded in a single-bond geometry to one C(8) atom. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Er(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Er(2) and one C(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Er(1) and one C(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one C(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Er(1) and one C(3) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Er(2) and one C(3) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Er(1) and one C(4) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Er(2) and one C(4) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(5) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Er(2) and one C(5) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(6) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Er(1) and one C(6) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Er(1) and one C(7) atom. In the fourteenth O site, O(14) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one C(7) atom. In the fifteenth O site, O(15) is bonded in a distorted single-bond geometry to one Er(2) and one C(8) atom. In the sixteenth O site, O(16) is bonded in a distorted single-bond geometry to one Er(2) and one C(8) atom. Linkers: 32 [O]C=O. Metal clusters: 8 [Er]. The MOF has largest included sphere 3.99 A, density 2.22 g/cm3, surface area 2405.27 m2/g, accessible volume 0.16 cm3/g