CaC6H2O5 crystallizes in the triclinic P-1 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), one O(5), one O(6), one O(7), and one O(9) atom. The Ca(1)-O(2) bond length is 2.38 Å. The Ca(1)-O(4) bond length is 2.51 Å. The Ca(1)-O(5) bond length is 2.49 Å. The Ca(1)-O(6) bond length is 2.38 Å. The Ca(1)-O(7) bond length is 2.30 Å. The Ca(1)-O(9) bond length is 2.37 Å. In the second Ca site, Ca(2) is bonded in a hexagonal planar geometry to two equivalent O(6), two equivalent O(8), and two equivalent O(9) atoms. Both Ca(2)-O(6) bond lengths are 2.42 Å. Both Ca(2)-O(8) bond lengths are 2.54 Å. Both Ca(2)-O(9) bond lengths are 2.80 Å. In the third Ca site, Ca(3) is bonded in an octahedral geometry to two equivalent O(1), two equivalent O(10), and two equivalent O(5) atoms. Both Ca(3)-O(1) bond lengths are 2.31 Å. Both Ca(3)-O(10) bond lengths are 2.33 Å. Both Ca(3)-O(5) bond lengths are 2.33 Å. There are twelve inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.49 Å. The C(1)-O(1) bond length is 1.26 Å. The C(1)-O(2) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted trigonal planar geometry to one C(1), one C(3), and one O(3) atom. The C(2)-C(3) bond length is 1.35 Å. The C(2)-O(3) bond length is 1.37 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2) and one H(1) atom. The C(3)-H(1) bond length is 0.93 Å. In the fourth C site, C(4) is bonded in a single-bond geometry to one C(5) and one H(2) atom. The C(4)-C(5) bond length is 1.34 Å. The C(4)-H(2) bond length is 0.93 Å. In the fifth C site, C(5) is bonded in a distorted single-bond geometry to one C(4), one C(6), and one O(3) atom. The C(5)-C(6) bond length is 1.48 Å. The C(5)-O(3) bond length is 1.37 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(5), one O(4), and one O(5) atom. The C(6)-O(4) bond length is 1.25 Å. The C(6)-O(5) bond length is 1.27 Å. In the seventh C site, C(7) is bonded in a distorted bent 120 degrees geometry to one C(8), one O(6), and one O(7) atom. The C(7)-C(8) bond length is 1.47 Å. The C(7)-O(6) bond length is 1.26 Å. The C(7)-O(7) bond length is 1.24 Å. In the eighth C site, C(8) is bonded in a distorted single-bond geometry to one C(7), one C(9), and one O(8) atom. The C(8)-C(9) bond length is 1.34 Å. The C(8)-O(8) bond length is 1.37 Å. In the ninth C site, C(9) is bonded in a distorted single-bond geometry to one C(8) and one H(3) atom. The C(9)-H(3) bond length is 0.93 Å. In the tenth C site, C(10) is bonded in a distorted single-bond geometry to one C(11) and one H(4) atom. The C(10)-C(11) bond length is 1.35 Å. The C(10)-H(4) bond length is 0.93 Å. In the eleventh C site, C(11) is bonded in a 3-coordinate geometry to one C(10), one C(12), and one O(8) atom. The C(11)-C(12) bond length is 1.48 Å. The C(11)-O(8) bond length is 1.37 Å. In the twelfth C site, C(12) is bonded in a distorted bent 120 degrees geometry to one C(11), one O(10), and one O(9) atom. The C(12)-O(10) bond length is 1.24 Å. The C(12)-O(9) bond length is 1.26 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(3) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(4) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(9) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(10) atom. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Ca(3) and one C(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ca(1) and one C(1) atom. In the third O site, O(3) is bonded in a water-like geometry to one C(2) and one C(5) atom. In the fourth O site, O(4) is bonded in a distorted L-shaped geometry to one Ca(1) and one C(6) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one C(6) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(2), and one C(7) atom. In the seventh O site, O(7) is bonded in a distorted linear geometry to one Ca(1) and one C(7) atom. In the eighth O site, O(8) is bonded in a distorted water-like geometry to one Ca(2), one C(11), and one C(8) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Ca(2), and one C(12) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Ca(3) and one C(12) atom. Linkers: 2 [O]C(=O)c1ccc(C([O])=O)o1. Metal clusters: 4 [Ca]. The MOF has largest included sphere 5.78 A, density 1.17 g/cm3, surface area 3769.15 m2/g, accessible volume 0.48 cm3/g