Ca2Cu(HCOO)6 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded to one O(1), one O(3), one O(6), two equivalent O(4), and two equivalent O(5) atoms to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Cu(1)O6 octahedra and edges with two equivalent Ca(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 41°. The Ca(1)-O(1) bond length is 2.34 Å. The Ca(1)-O(3) bond length is 2.57 Å. The Ca(1)-O(6) bond length is 2.27 Å. There is one shorter (2.40 Å) and one longer (2.66 Å) Ca(1)-O(4) bond length. There is one shorter (2.36 Å) and one longer (2.42 Å) Ca(1)-O(5) bond length. Cu(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form distorted CuO6 octahedra that share corners with two equivalent Ca(1)O7 pentagonal bipyramids and edges with two equivalent Cu(1)O6 octahedra. Both Cu(1)-O(3) bond lengths are 1.99 Å. There are two shorter (1.97 Å) and two longer (2.56 Å) Cu(1)-O(2) bond lengths. There are three 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(2) atom. The C(1)-H(1) bond length is 1.10 Å. The C(1)-O(1) bond length is 1.25 Å. The C(1)-O(2) bond length is 1.29 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one H(2), one O(3), and one O(4) atom. The C(2)-H(2) bond length is 1.11 Å. The C(2)-O(3) bond length is 1.28 Å. The C(2)-O(4) bond length is 1.26 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one H(3), one O(5), and one O(6) atom. The C(3)-H(3) bond length is 1.11 Å. The C(3)-O(5) bond length is 1.28 Å. The C(3)-O(6) bond length is 1.26 Å. There are three 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. In the third H site, H(3) is bonded in a single-bond geometry to one C(3) atom. There are six inequivalent O sites. In the first O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Cu(1) and one C(1) atom. In the second O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Cu(1), and one C(2) atom. In the third O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(2) atom. In the fourth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one C(3) atom. In the fifth O site, O(6) is bonded in a distorted linear geometry to one Ca(1) and one C(3) atom. In the sixth O site, O(1) is bonded in a bent 150 degrees geometry to one Ca(1) and one C(1) atom. Linkers: 12 [O]C=O. Metal clusters: 4 [Ca] ,2 [Cu]. The MOF has largest included sphere 1.42 A, density 2.22 g/cm3, surface area 3117.73 m2/g, accessible volume 0.01 cm3/g