MgH6(CO3)2 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 two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. Both Mg(1)-O(1) bond lengths are 2.09 Å. Both Mg(1)-O(2) bond lengths are 2.07 Å. Both Mg(1)-O(4) bond lengths are 2.11 Å. In the second Mg site, Mg(2) is bonded in an octahedral geometry to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. Both Mg(2)-O(3) bond lengths are 2.15 Å. Both Mg(2)-O(5) bond lengths are 2.09 Å. Both Mg(2)-O(6) bond lengths are 2.06 Å. There are two inequivalent C sites. In the first C site, C(2) is bonded in a trigonal planar geometry to one H(3), one O(3), and one O(4) atom. The C(2)-H(3) bond length is 1.11 Å. The C(2)-O(3) bond length is 1.27 Å. The C(2)-O(4) bond length is 1.28 Å. In the second C site, C(1) is bonded in a trigonal planar geometry to one H(4), one O(1), and one O(2) atom. The C(1)-H(4) bond length is 1.10 Å. The C(1)-O(1) bond length is 1.27 Å. The C(1)-O(2) bond length is 1.27 Å. There are six inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(2) and one O(5) atom. The H(1)-O(2) bond length is 1.74 Å. The H(1)-O(5) bond length is 0.99 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(5) atom. The H(2)-O(5) bond length is 1.00 Å. In the third H site, H(3) is bonded in a single-bond geometry to one C(2) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(1) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(3) and one O(6) atom. The H(5)-O(3) bond length is 1.71 Å. The H(5)-O(6) bond length is 1.00 Å. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(6) atom. The H(6)-O(6) bond length is 0.99 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Mg(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one C(1), and one H(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(2), one C(2), and one H(5) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Mg(1) and one C(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Mg(2), one H(1), and one H(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(2), one H(5), and one H(6) atom. Linkers: 8 [O]C=O. Metal clusters: 4 [Mg]. The MOF has largest included sphere 1.70 A, density 1.76 g/cm3, surface area 3924.88 m2/g, accessible volume 0.11 cm3/g