ErH4(CO2)4 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 8-coordinate geometry to one O(1), one O(15), one O(17), one O(19), one O(2), one O(21), one O(23), and one O(9) atom. The Er(1)-O(1) bond length is 2.38 Å. The Er(1)-O(15) bond length is 2.33 Å. The Er(1)-O(17) bond length is 2.36 Å. The Er(1)-O(19) bond length is 2.37 Å. The Er(1)-O(2) bond length is 2.41 Å. The Er(1)-O(21) bond length is 2.30 Å. The Er(1)-O(23) bond length is 2.33 Å. The Er(1)-O(9) bond length is 2.32 Å. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(24), one O(25), one O(26), one O(27), one O(3), and one O(4) atom. The Er(2)-O(10) bond length is 2.30 Å. The Er(2)-O(11) bond length is 2.24 Å. The Er(2)-O(24) bond length is 2.31 Å. The Er(2)-O(25) bond length is 2.39 Å. The Er(2)-O(26) bond length is 2.37 Å. The Er(2)-O(27) bond length is 2.32 Å. The Er(2)-O(3) bond length is 2.45 Å. The Er(2)-O(4) bond length is 2.38 Å. In the third Er site, Er(3) is bonded in a 8-coordinate geometry to one O(12), one O(13), one O(16), one O(29), one O(31), one O(32), one O(5), and one O(6) atom. The Er(3)-O(12) bond length is 2.33 Å. The Er(3)-O(13) bond length is 2.33 Å. The Er(3)-O(16) bond length is 2.32 Å. The Er(3)-O(29) bond length is 2.32 Å. The Er(3)-O(31) bond length is 2.35 Å. The Er(3)-O(32) bond length is 2.35 Å. The Er(3)-O(5) bond length is 2.36 Å. The Er(3)-O(6) bond length is 2.42 Å. In the fourth Er site, Er(4) is bonded in a 8-coordinate geometry to one O(14), one O(18), one O(20), one O(22), one O(28), one O(30), one O(7), and one O(8) atom. The Er(4)-O(14) bond length is 2.33 Å. The Er(4)-O(18) bond length is 2.38 Å. The Er(4)-O(20) bond length is 2.37 Å. The Er(4)-O(22) bond length is 2.27 Å. The Er(4)-O(28) bond length is 2.29 Å. The Er(4)-O(30) bond length is 2.29 Å. The Er(4)-O(7) bond length is 2.42 Å. The Er(4)-O(8) bond length is 2.40 Å. There are sixteen 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 0.95 Å. The C(1)-O(1) bond length is 1.25 Å. The C(1)-O(2) bond length is 1.23 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 0.95 Å. The C(2)-O(3) 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 trigonal planar geometry to one H(3), one O(5), and one O(6) atom. The C(3)-H(3) bond length is 0.95 Å. The C(3)-O(5) bond length is 1.24 Å. The C(3)-O(6) bond length is 1.22 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 0.95 Å. The C(4)-O(7) bond length is 1.23 Å. The C(4)-O(8) bond length is 1.26 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 0.95 Å. The C(5)-O(10) bond length is 1.23 Å. The C(5)-O(9) bond length is 1.25 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 0.95 Å. The C(6)-O(11) bond length is 1.25 Å. The C(6)-O(12) bond length is 1.21 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 0.95 Å. The C(7)-O(13) bond length is 1.25 Å. The C(7)-O(14) bond length is 1.23 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 0.95 Å. The C(8)-O(15) bond length is 1.24 Å. The C(8)-O(16) bond length is 1.24 Å. In the ninth C site, C(9) is bonded in a trigonal planar geometry to one H(9), one O(17), and one O(18) atom. The C(9)-H(9) bond length is 0.95 Å. The C(9)-O(17) bond length is 1.24 Å. The C(9)-O(18) bond length is 1.25 Å. In the tenth C site, C(10) is bonded in a trigonal planar geometry to one H(10), one O(19), and one O(20) atom. The C(10)-H(10) bond length is 0.95 Å. The C(10)-O(19) bond length is 1.26 Å. The C(10)-O(20) bond length is 1.23 Å. In the eleventh C site, C(11) is bonded in a trigonal planar geometry to one H(11), one O(21), and one O(22) atom. The C(11)-H(11) bond length is 0.95 Å. The C(11)-O(21) bond length is 1.21 Å. The C(11)-O(22) bond length is 1.24 Å. In the twelfth C site, C(12) is bonded in a trigonal planar geometry to one H(12), one O(23), and one O(24) atom. The C(12)-H(12) bond length is 0.95 Å. The C(12)-O(23) bond length is 1.23 Å. The C(12)-O(24) bond length is 1.24 Å. In the thirteenth C site, C(13) is bonded in a trigonal planar geometry to one H(13), one O(25), and one O(26) atom. The C(13)-H(13) bond length is 0.95 Å. The C(13)-O(25) bond length is 1.24 Å. The C(13)-O(26) bond length is 1.27 Å. In the fourteenth C site, C(14) is bonded in a trigonal planar geometry to one H(14), one O(27), and one O(28) atom. The C(14)-H(14) bond length is 0.95 Å. The C(14)-O(27) bond length is 1.22 Å. The C(14)-O(28) bond length is 1.23 Å. In the fifteenth C site, C(15) is bonded in a trigonal planar geometry to one H(15), one O(29), and one O(30) atom. The C(15)-H(15) bond length is 0.95 Å. The C(15)-O(29) bond length is 1.24 Å. The C(15)-O(30) bond length is 1.22 Å. In the sixteenth C site, C(16) is bonded in a trigonal planar geometry to one H(16), one O(31), and one O(32) atom. The C(16)-H(16) bond length is 0.95 Å. The C(16)-O(31) bond length is 1.24 Å. The C(16)-O(32) bond length is 1.24 Å. There are sixteen 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. In the ninth H site, H(9) is bonded in a single-bond geometry to one C(9) atom. In the tenth H site, H(10) is bonded in a single-bond geometry to one C(10) atom. In the eleventh H site, H(11) is bonded in a single-bond geometry to one C(11) atom. In the twelfth H site, H(12) is bonded in a single-bond geometry to one C(12) atom. In the thirteenth H site, H(13) is bonded in a single-bond geometry to one C(13) atom. In the fourteenth H site, H(14) is bonded in a single-bond geometry to one C(14) atom. In the fifteenth H site, H(15) is bonded in a single-bond geometry to one C(15) atom. In the sixteenth H site, H(16) is bonded in a single-bond geometry to one C(16) atom. There are thirty-two inequivalent O sites. In the first O site, O(8) is bonded in an L-shaped geometry to one Er(4) and one C(4) atom. In the second O site, O(9) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one C(5) atom. In the third O site, O(10) is bonded in a bent 150 degrees geometry to one Er(2) and one C(5) atom. In the fourth O site, O(11) is bonded in a linear geometry to one Er(2) and one C(6) atom. In the fifth O site, O(12) is bonded in a bent 150 degrees geometry to one Er(3) and one C(6) atom. In the sixth O site, O(13) is bonded in a distorted bent 150 degrees geometry to one Er(3) and one C(7) atom. In the seventh O site, O(14) is bonded in a distorted bent 150 degrees geometry to one Er(4) and one C(7) atom. In the eighth O site, O(15) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one C(8) atom. In the ninth O site, O(16) is bonded in a bent 150 degrees geometry to one Er(3) and one C(8) atom. In the tenth O site, O(17) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(9) atom. In the eleventh O site, O(1) is bonded in an L-shaped geometry to one Er(1) and one C(1) atom. In the twelfth O site, O(18) is bonded in a distorted bent 120 degrees geometry to one Er(4) and one C(9) atom. In the thirteenth O site, O(20) is bonded in a distorted bent 120 degrees geometry to one Er(4) and one C(10) atom. In the fourteenth O site, O(21) is bonded in a bent 150 degrees geometry to one Er(1) and one C(11) atom. In the fifteenth O site, O(22) is bonded in a linear geometry to one Er(4) and one C(11) atom. In the sixteenth O site, O(23) is bonded in a distorted single-bond geometry to one Er(1) and one C(12) atom. In the seventeenth O site, O(19) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(10) atom. In the eighteenth O site, O(25) is bonded in a bent 120 degrees geometry to one Er(2) and one C(13) atom. In the nineteenth O site, O(26) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one C(13) atom. In the twentieth O site, O(27) is bonded in a distorted bent 150 degrees geometry to one Er(2) and one C(14) atom. In the twenty-first O site, O(28) is bonded in a bent 150 degrees geometry to one Er(4) and one C(14) atom. In the twenty-second O site, O(29) is bonded in a distorted bent 150 degrees geometry to one Er(3) and one C(15) atom. In the twenty-third O site, O(30) is bonded in a distorted bent 150 degrees geometry to one Er(4) and one C(15) atom. In the twenty-fourth O site, O(31) is bonded in a distorted bent 120 degrees geometry to one Er(3) and one C(16) atom. In the twenty-fifth O site, O(32) is bonded in a distorted bent 120 degrees geometry to one Er(3) and one C(16) atom. In the twenty-sixth O site, O(24) is bonded in a 2-coordinate geometry to one Er(2) and one C(12) atom. In the twenty-seventh O site, O(2) is bonded in a distorted L-shaped geometry to one Er(1) and one C(1) atom. In the twenty-eighth O site, O(3) is bonded in a distorted single-bond geometry to one Er(2) and one C(2) atom. In the twenty-ninth O site, O(4) is bonded in an L-shaped geometry to one Er(2) and one C(2) atom. In the thirtieth O site, O(5) is bonded in an L-shaped geometry to one Er(3) and one C(3) atom. In the thirty-first O site, O(6) is bonded in a distorted L-shaped geometry to one Er(3) and one C(3) atom. In the thirty-second O site, O(7) is bonded in a distorted L-shaped geometry to one Er(4) and one C(4) atom. Linkers: 50 [O]C=O. Metal clusters: 16 [Er]. The MOF has largest included sphere 4.38 A, density 1.98 g/cm3, surface area 2672.82 m2/g, accessible volume 0.24 cm3/g