Ba(CO)4 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted hexagonal planar geometry to one O(10), one O(2), one O(3), one O(8), and two equivalent O(9) atoms. The Ba(1)-O(10) bond length is 2.82 Å. The Ba(1)-O(2) bond length is 2.66 Å. The Ba(1)-O(3) bond length is 2.88 Å. The Ba(1)-O(8) bond length is 2.70 Å. There is one shorter (2.76 Å) and one longer (2.86 Å) Ba(1)-O(9) bond length. In the second Ba site, Ba(2) is bonded in a 5-coordinate geometry to one O(10), one O(11), one O(2), and two equivalent O(1) atoms. The Ba(2)-O(10) bond length is 2.78 Å. The Ba(2)-O(11) bond length is 2.81 Å. The Ba(2)-O(2) bond length is 2.77 Å. There is one shorter (2.69 Å) and one longer (2.84 Å) Ba(2)-O(1) bond length. In the third Ba site, Ba(3) is bonded in a distorted hexagonal planar geometry to one O(3), one O(8), two equivalent O(5), and two equivalent O(6) atoms. The Ba(3)-O(3) bond length is 2.72 Å. The Ba(3)-O(8) bond length is 2.81 Å. There is one shorter (2.70 Å) and one longer (2.93 Å) Ba(3)-O(5) bond length. There is one shorter (2.72 Å) and one longer (2.75 Å) Ba(3)-O(6) bond length. There are twelve inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one C(11), one C(2), and one C(3) atom. The C(1)-C(11) bond length is 1.40 Å. The C(1)-C(2) bond length is 1.50 Å. The C(1)-C(3) bond length is 1.39 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one C(1), one O(1), and one O(2) atom. The C(2)-O(1) bond length is 1.25 Å. The C(2)-O(2) bond length is 1.26 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one C(1), one C(4), and one C(5) atom. The C(3)-C(4) bond length is 1.50 Å. The C(3)-C(5) bond length is 1.40 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(3), and one O(4) atom. The C(4)-O(3) bond length is 1.26 Å. The C(4)-O(4) bond length is 1.26 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one C(3), one C(6), and one C(7) atom. The C(5)-C(6) bond length is 1.50 Å. The C(5)-C(7) bond length is 1.39 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(5), one O(5), and one O(6) atom. The C(6)-O(5) bond length is 1.25 Å. The C(6)-O(6) bond length is 1.27 Å. In the seventh C site, C(7) is bonded in a trigonal planar geometry to one C(5), one C(8), and one C(9) atom. The C(7)-C(8) bond length is 1.52 Å. The C(7)-C(9) bond length is 1.40 Å. In the eighth C site, C(8) is bonded in a distorted bent 120 degrees geometry to one C(7), one O(7), and one O(8) atom. The C(8)-O(7) bond length is 1.25 Å. The C(8)-O(8) bond length is 1.24 Å. In the ninth C site, C(9) is bonded in a trigonal planar geometry to one C(10), one C(11), and one C(7) atom. The C(9)-C(10) bond length is 1.49 Å. The C(9)-C(11) bond length is 1.39 Å. In the tenth C site, C(10) is bonded in a distorted bent 120 degrees geometry to one C(9), one O(10), and one O(9) atom. The C(10)-O(10) bond length is 1.27 Å. The C(10)-O(9) bond length is 1.26 Å. In the eleventh C site, C(11) is bonded in a trigonal planar geometry to one C(1), one C(12), and one C(9) atom. The C(11)-C(12) bond length is 1.52 Å. In the twelfth C site, C(12) is bonded in a distorted bent 120 degrees geometry to one C(11), one O(11), and one O(12) atom. The C(12)-O(11) bond length is 1.25 Å. The C(12)-O(12) bond length is 1.27 Å. There are twelve inequivalent O sites. In the first O site, O(9) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one C(10) atom. In the second O site, O(10) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(10) atom. In the third O site, O(11) is bonded in a single-bond geometry to one Ba(2) and one C(12) atom. In the fourth O site, O(12) is bonded in a single-bond geometry to one C(12) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Ba(2) and one C(2) atom. In the sixth O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(2) atom. In the seventh O site, O(3) is bonded in a single-bond geometry to one Ba(1), one Ba(3), and one C(4) atom. In the eighth O site, O(4) is bonded in a single-bond geometry to one C(4) atom. In the ninth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent Ba(3) and one C(6) atom. In the tenth O site, O(6) is bonded in a distorted single-bond geometry to two equivalent Ba(3) and one C(6) atom. In the eleventh O site, O(7) is bonded in a single-bond geometry to one C(8) atom. In the twelfth O site, O(8) is bonded in a single-bond geometry to one Ba(1), one Ba(3), and one C(8) atom. Linkers: 8 [O]C(=O)c1c(C([O])=O)c(C([O])=O)c(C([O])=O)c(C([O])=O)c1C([O])=O. Metal clusters: 24 [Ba]. The MOF has largest included sphere 8.78 A, density 1.65 g/cm3, surface area 2268.39 m2/g, accessible volume 0.32 cm3/g