K2CaZrH16(CO3)8 crystallizes in the tetragonal I-4 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(5) atoms. All K(1)-O(1) bond lengths are 2.82 Å. All K(1)-O(5) bond lengths are 2.94 Å. In the second K site, K(2) is bonded in a 8-coordinate geometry to four equivalent O(4) and four equivalent O(6) atoms. All K(2)-O(4) bond lengths are 2.74 Å. All K(2)-O(6) bond lengths are 2.96 Å. Ca(1) is bonded in a 8-coordinate geometry to four equivalent O(3) and four equivalent O(4) atoms. All Ca(1)-O(3) bond lengths are 2.42 Å. All Ca(1)-O(4) bond lengths are 2.51 Å. Zr(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. All Zr(1)-O(1) bond lengths are 2.25 Å. All Zr(1)-O(2) bond lengths are 2.21 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(3) atom. The C(1)-O(1) bond length is 1.28 Å. The C(1)-O(3) bond length is 1.25 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one O(2) and one O(4) atom. The C(2)-O(2) bond length is 1.30 Å. The C(2)-O(4) bond length is 1.24 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 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 0.99 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 1.00 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(6) atom. The H(4)-O(6) bond length is 0.98 Å. There are six inequivalent O sites. In the first O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one C(1) atom. In the second O site, O(4) is bonded in a distorted single-bond geometry to one K(2), one Ca(1), and one C(2) atom. In the third O site, O(5) is bonded in a water-like geometry to one K(1), one H(1), and one H(2) atom. In the fourth O site, O(6) is bonded in a water-like geometry to one K(2), one H(3), and one H(4) atom. In the fifth O site, O(1) is bonded in a 1-coordinate geometry to one K(1), one Zr(1), and one C(1) atom. In the sixth O site, O(2) is bonded in a bent 120 degrees geometry to one Zr(1) and one C(2) atom. Linkers: 4 [O]C(=O)C([O])=O. Metal clusters: 2 [K] ,1 [Ca] ,1 [Zr]. The MOF has largest included sphere 1.48 A, density 2.04 g/cm3, surface area 2420.73 m2/g, accessible volume 0.06 cm3/g