K2MgRu2(CO3)4 crystallizes in the orthorhombic Pccn space group. K(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. The K(1)-O(2) bond length is 2.95 Å. There is one shorter (2.68 Å) and one longer (3.17 Å) K(1)-O(1) bond length. There is one shorter (3.03 Å) and one longer (3.08 Å) K(1)-O(3) bond length. Mg(1) is bonded in an L-shaped geometry to two equivalent O(6) atoms. Both Mg(1)-O(6) bond lengths are 2.07 Å. Ru(1) is bonded in a distorted square pyramidal geometry to one O(1), one O(2), one O(3), one O(4), and one O(5) atom. The Ru(1)-O(1) bond length is 2.03 Å. The Ru(1)-O(2) bond length is 2.03 Å. The Ru(1)-O(3) bond length is 2.26 Å. The Ru(1)-O(4) bond length is 2.02 Å. The Ru(1)-O(5) bond length is 2.01 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(3) atom. The C(1)-O(1) bond length is 1.29 Å. The C(1)-O(2) bond length is 1.30 Å. The C(1)-O(3) bond length is 1.26 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one O(4), one O(5), and one O(6) atom. The C(2)-O(4) bond length is 1.29 Å. The C(2)-O(5) bond length is 1.31 Å. The C(2)-O(6) bond length is 1.26 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ru(1), and one C(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Ru(1), and one C(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ru(1), and one C(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Ru(1) and one C(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Ru(1) and one C(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(2) atom. Linkers: 16 [O]C([O])=O. Metal clusters: 8 [K] ,4 [Mg] ,8 [Ru]. The MOF has largest included sphere 4.16 A, density 2.08 g/cm3, surface area 2196.31 m2/g, accessible volume 0.13 cm3/g