MgH3(CO2)3 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in an octahedral geometry to one O(12), one O(2), one O(3), one O(4), one O(5), and one O(6) atom. The Mg(1)-O(12) bond length is 2.05 Å. The Mg(1)-O(2) bond length is 2.04 Å. The Mg(1)-O(3) bond length is 2.07 Å. The Mg(1)-O(4) bond length is 2.07 Å. The Mg(1)-O(5) bond length is 2.08 Å. The Mg(1)-O(6) bond length is 2.06 Å. In the second Mg site, Mg(2) is bonded in an octahedral geometry to one O(1), one O(10), one O(11), one O(7), one O(8), and one O(9) atom. The Mg(2)-O(1) bond length is 2.09 Å. The Mg(2)-O(10) bond length is 2.05 Å. The Mg(2)-O(11) bond length is 2.07 Å. The Mg(2)-O(7) bond length is 2.06 Å. The Mg(2)-O(8) bond length is 2.05 Å. The Mg(2)-O(9) bond length is 2.06 Å. There are six 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(6) atom. The C(1)-H(1) bond length is 0.93 Å. The C(1)-O(1) bond length is 1.25 Å. The C(1)-O(6) bond length is 1.22 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one H(2), one O(12), and one O(7) atom. The C(2)-H(2) bond length is 0.93 Å. The C(2)-O(12) bond length is 1.23 Å. The C(2)-O(7) bond length is 1.21 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one H(3), one O(11), and one O(4) atom. The C(3)-H(3) bond length is 0.93 Å. The C(3)-O(11) bond length is 1.22 Å. The C(3)-O(4) bond length is 1.24 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one H(4), one O(10), and one O(3) atom. The C(4)-H(4) bond length is 0.93 Å. The C(4)-O(10) bond length is 1.23 Å. The C(4)-O(3) bond length is 1.25 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one H(5), one O(5), and one O(9) atom. The C(5)-H(5) bond length is 0.93 Å. The C(5)-O(5) bond length is 1.23 Å. The C(5)-O(9) bond length is 1.23 Å. In the sixth C site, C(6) is bonded in a trigonal planar geometry to one H(6), one O(2), and one O(8) atom. The C(6)-H(6) bond length is 0.93 Å. The C(6)-O(2) bond length is 1.21 Å. The C(6)-O(8) bond length is 1.22 Å. There are six 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. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(6) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one C(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(5) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one C(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Mg(2) and one C(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Mg(2) and one C(6) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Mg(2) and one C(5) atom. In the tenth O site, O(10) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one C(4) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Mg(2) and one C(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(2) atom. Linkers: 24 [O]C=O. Metal clusters: 8 [Mg]. The MOF has largest included sphere 4.57 A, density 1.14 g/cm3, surface area 4724.78 m2/g, accessible volume 0.41 cm3/g