Ca(C2O)4 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms. The Ca(1)-O(1) bond length is 2.59 Å. The Ca(1)-O(3) bond length is 2.52 Å. There is one shorter (2.43 Å) and one longer (2.64 Å) Ca(1)-O(2) bond length. There is one shorter (2.44 Å) and one longer (2.49 Å) Ca(1)-O(4) bond length. There are eight inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(4), one O(2), and one O(4) atom. The C(1)-C(4) bond length is 1.45 Å. The C(1)-O(2) bond length is 1.22 Å. The C(1)-O(4) bond length is 1.22 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(1), and one O(3) atom. The C(2)-C(3) bond length is 1.41 Å. The C(2)-O(1) bond length is 1.24 Å. The C(2)-O(3) bond length is 1.24 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one C(2), one C(5), and one C(7) atom. The C(3)-C(5) bond length is 1.41 Å. The C(3)-C(7) bond length is 1.42 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one C(1), one C(6), and one C(8) atom. The C(4)-C(6) bond length is 1.38 Å. The C(4)-C(8) bond length is 1.45 Å. In the fifth C site, C(5) is bonded in a bent 120 degrees geometry to one C(3) and one C(7) atom. The C(5)-C(7) bond length is 1.50 Å. In the sixth C site, C(6) is bonded in a bent 120 degrees geometry to one C(4) and one C(8) atom. The C(6)-C(8) bond length is 1.44 Å. In the seventh C site, C(7) is bonded in a bent 120 degrees geometry to one C(3) and one C(5) atom. In the eighth C site, C(8) is bonded in a bent 120 degrees geometry to one C(4) and one C(6) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted L-shaped geometry to one Ca(1) and one C(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(1) atom. In the third O site, O(3) is bonded in an L-shaped geometry to one Ca(1) and one C(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one C(1) atom. Linkers: 2 [O]C(=O)c1[c][c]c(C([O])=O)[c][c]1. Metal clusters: 2 [Ca]. RCSR code: bex. The MOF has largest included sphere 5.75 A, density 0.90 g/cm3, surface area 4557.83 m2/g, accessible volume 0.57 cm3/g