CaCu(HCOO)4 crystallizes in the monoclinic P2/c space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), and four equivalent O(2) atoms. Both Ca(1)-O(3) bond lengths are 2.62 Å. Both Ca(1)-O(4) bond lengths are 2.30 Å. There are two shorter (2.38 Å) and two longer (2.62 Å) Ca(1)-O(2) bond lengths. Cu(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Both Cu(1)-O(3) bond lengths are 1.98 Å. There are two shorter (1.97 Å) and two longer (2.58 Å) Cu(1)-O(1) bond lengths. There are two inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one H(1), one O(1), and one O(4) atom. The C(1)-H(1) bond length is 1.11 Å. The C(1)-O(1) bond length is 1.29 Å. The C(1)-O(4) bond length is 1.25 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one H(2), one O(2), and one O(3) atom. The C(2)-H(2) bond length is 1.11 Å. The C(2)-O(2) bond length is 1.26 Å. The C(2)-O(3) bond length is 1.28 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(2) atom. There are four inequivalent O sites. In the first O site, O(4) is bonded in a bent 150 degrees geometry to one Ca(1) and one C(1) atom. In the second O site, O(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Cu(1) and one C(1) atom. In the third O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Cu(1), and one C(2) atom. Linkers: 8 [O]C=O. Metal clusters: 2 [Ca] ,2 [Cu]. The MOF has largest included sphere 1.37 A, density 2.35 g/cm3, surface area 2828.32 m2/g, accessible volume 0.05 cm3/g