BaH4(CO3)2 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 10-coordinate geometry to one O(2), one O(6), two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. The Ba(1)-O(2) bond length is 2.74 Å. The Ba(1)-O(6) bond length is 2.90 Å. There is one shorter (2.86 Å) and one longer (3.34 Å) Ba(1)-O(1) bond length. There is one shorter (2.81 Å) and one longer (2.86 Å) Ba(1)-O(3) bond length. There is one shorter (2.85 Å) and one longer (3.03 Å) Ba(1)-O(4) bond length. Both Ba(1)-O(5) bond lengths are 2.87 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(2) atom. The C(1)-O(1) bond length is 1.27 Å. The C(1)-O(2) bond length is 1.27 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one O(3) and one O(4) atom. The C(2)-O(3) bond length is 1.26 Å. The C(2)-O(4) bond length is 1.28 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(5) atom. The H(1)-O(5) bond length is 1.00 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 O(6) atom. The H(3)-O(6) bond length is 0.99 Å. In the fourth H site, H(4) is bonded in a distorted single-bond geometry to one O(6) atom. The H(4)-O(6) bond length is 1.00 Å. There are six inequivalent O sites. In the first O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1) and one C(1) atom. In the second O site, O(3) is bonded in a single-bond geometry to two equivalent Ba(1) and one C(2) atom. In the third O site, O(4) is bonded in a 1-coordinate geometry to two equivalent Ba(1) and one C(2) atom. In the fourth O site, O(5) is bonded in a water-like geometry to two equivalent Ba(1), one H(1), and one H(2) atom. In the fifth O site, O(6) is bonded in a water-like geometry to one Ba(1), one H(3), and one H(4) atom. In the sixth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one C(1) atom. Linkers: 4 [O]C(=O)C([O])=O. Metal clusters: 4 [Ba]. The MOF has largest included sphere 1.58 A, density 3.06 g/cm3, surface area 2043.52 m2/g, accessible volume 0.03 cm3/g