CaC6H2SO4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(3), one O(6), one O(7), and two equivalent O(2) atoms to form distorted CaO6 pentagonal pyramids that share  an edgeedge with one Ca(1)O6 pentagonal pyramid and  an edgeedge with one Ca(2)O5 square pyramid. The Ca(1)-O(1) bond length is 2.50 Å. The Ca(1)-O(3) bond length is 2.48 Å. The Ca(1)-O(6) bond length is 2.29 Å. The Ca(1)-O(7) bond length is 2.36 Å. There is one shorter (2.29 Å) and one longer (2.44 Å) Ca(1)-O(2) bond length. In the second Ca site, Ca(2) is bonded to one O(1), one O(3), one O(4), one O(5), and one O(8) atom to form edge-sharing CaO5 square pyramids. The Ca(2)-O(1) bond length is 2.43 Å. The Ca(2)-O(3) bond length is 2.34 Å. The Ca(2)-O(4) bond length is 2.26 Å. The Ca(2)-O(5) bond length is 2.30 Å. The Ca(2)-O(8) bond length is 2.32 Å. There are twelve inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one C(2), one C(9), and one S(1) atom. The C(1)-C(2) bond length is 1.47 Å. The C(1)-C(9) bond length is 1.37 Å. The C(1)-S(1) bond length is 1.71 Å. In the second C site, C(2) is bonded in a bent 120 degrees geometry to one C(1), one O(1), and one O(2) atom. The C(2)-O(1) bond length is 1.26 Å. The C(2)-O(2) bond length is 1.26 Å. In the third C site, C(3) is bonded in a trigonal planar geometry to one C(10), one C(4), and one S(1) atom. The C(3)-C(10) bond length is 1.36 Å. The C(3)-C(4) bond length is 1.47 Å. The C(3)-S(1) bond length is 1.71 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(3), and one O(7) atom. The C(4)-O(3) bond length is 1.26 Å. The C(4)-O(7) bond length is 1.25 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one C(12), one C(8), and one S(2) atom. The C(5)-C(12) bond length is 1.49 Å. The C(5)-C(8) bond length is 1.35 Å. The C(5)-S(2) bond length is 1.72 Å. In the sixth C site, C(6) is bonded in a distorted single-bond geometry to one C(7) and one H(1) atom. The C(6)-C(7) bond length is 1.35 Å. The C(6)-H(1) bond length is 0.93 Å. In the seventh C site, C(7) is bonded in a trigonal planar geometry to one C(11), one C(6), and one S(2) atom. The C(7)-C(11) bond length is 1.49 Å. The C(7)-S(2) bond length is 1.71 Å. In the eighth C site, C(8) is bonded in a distorted single-bond geometry to one C(5) and one H(2) atom. The C(8)-H(2) bond length is 0.93 Å. In the ninth C site, C(9) is bonded in a distorted single-bond geometry to one C(1) 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(3) and one H(4) atom. The C(10)-H(4) bond length is 0.93 Å. In the eleventh C site, C(11) is bonded in a distorted bent 120 degrees geometry to one C(7), one O(4), and one O(5) atom. The C(11)-O(4) bond length is 1.24 Å. The C(11)-O(5) bond length is 1.24 Å. In the twelfth C site, C(12) is bonded in a distorted bent 120 degrees geometry to one C(5), one O(6), and one O(8) atom. The C(12)-O(6) bond length is 1.26 Å. The C(12)-O(8) bond length is 1.25 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(6) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(8) 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 two inequivalent S sites. In the first S site, S(1) is bonded in an L-shaped geometry to one C(1) and one C(3) atom. In the second S site, S(2) is bonded in an L-shaped geometry to one C(5) and one C(7) atom. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Ca(1), one Ca(2), and one C(2) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to two equivalent Ca(1) and one C(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Ca(1), one Ca(2), and one C(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ca(2) and one C(11) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Ca(2) and one C(11) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Ca(1) and one C(12) atom. In the seventh O site, O(7) is bonded in an L-shaped geometry to one Ca(1) and one C(4) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Ca(2) and one C(12) atom. Linkers: 8 [O]C(=O)c1ccc(C([O])=O)s1. Metal clusters: 8 [Ca]. The MOF has largest included sphere 5.61 A, density 1.11 g/cm3, surface area 3907.40 m2/g, accessible volume 0.41 cm3/g