MgH18(C17O4)2 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.10 Å. Both Mg(1)-O(3) bond lengths are 2.09 Å. There are seventeen inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one C(2), one C(6), and one C(7) atom. The C(1)-C(2) bond length is 1.39 Å. The C(1)-C(6) bond length is 1.42 Å. The C(1)-C(7) bond length is 1.49 Å. In the second C site, C(2) is bonded in a distorted single-bond geometry to one C(1), one C(3), and one H(1) atom. The C(2)-C(3) bond length is 1.38 Å. The C(2)-H(1) bond length is 0.95 Å. In the third C site, C(3) is bonded in a distorted trigonal planar geometry to one C(2), one C(4), and one H(2) atom. The C(3)-C(4) bond length is 1.40 Å. The C(3)-H(2) bond length is 0.95 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one C(16), one C(3), and one C(5) atom. The C(4)-C(16) bond length is 1.50 Å. The C(4)-C(5) bond length is 1.38 Å. In the fifth C site, C(5) is bonded in a distorted single-bond geometry to one C(4) and one H(3) atom. The C(5)-H(3) bond length is 0.95 Å. In the sixth C site, C(6) is bonded in a distorted single-bond geometry to one C(1) and one H(4) atom. The C(6)-H(4) bond length is 0.95 Å. In the seventh C site, C(7) is bonded in a trigonal planar geometry to one C(1), one C(7), and one C(8) atom. The C(7)-C(7) bond length is 1.42 Å. The C(7)-C(8) bond length is 1.40 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 H(5) atom. The C(8)-C(9) bond length is 1.40 Å. The C(8)-H(5) bond length is 0.95 Å. In the ninth C site, C(9) is bonded in a trigonal planar geometry to one C(10), one C(8), and one C(9) atom. The C(9)-C(10) bond length is 1.50 Å. The C(9)-C(9) bond length is 1.39 Å. In the tenth C site, C(10) is bonded in a trigonal planar geometry to one C(11), one C(15), and one C(9) atom. The C(10)-C(11) bond length is 1.40 Å. The C(10)-C(15) bond length is 1.38 Å. In the eleventh C site, C(11) is bonded in a distorted single-bond geometry to one C(10) and one H(6) atom. The C(11)-H(6) bond length is 0.95 Å. In the twelfth C site, C(12) is bonded in a distorted single-bond geometry to one C(13) and one H(7) atom. The C(12)-C(13) bond length is 1.38 Å. The C(12)-H(7) bond length is 0.95 Å. In the thirteenth C site, C(13) is bonded in a trigonal planar geometry to one C(12), one C(14), and one C(17) atom. The C(13)-C(14) bond length is 1.39 Å. The C(13)-C(17) bond length is 1.49 Å. In the fourteenth C site, C(14) is bonded in a distorted trigonal planar geometry to one C(13), one C(15), and one H(8) atom. The C(14)-C(15) bond length is 1.40 Å. The C(14)-H(8) bond length is 0.95 Å. In the fifteenth C site, C(15) is bonded in a distorted single-bond geometry to one C(10), one C(14), and one H(9) atom. The C(15)-H(9) bond length is 0.95 Å. In the sixteenth C site, C(16) is bonded in a distorted bent 120 degrees geometry to one C(4), one O(1), and one O(2) atom. The C(16)-O(1) bond length is 1.24 Å. The C(16)-O(2) bond length is 1.27 Å. In the seventeenth C site, C(17) is bonded in a distorted bent 120 degrees geometry to one C(13), one O(3), and one O(4) atom. The C(17)-O(3) bond length is 1.23 Å. The C(17)-O(4) bond length is 1.30 Å. There are nine inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(2) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(3) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(5) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(6) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one C(8) atom. In the sixth H site, H(6) is bonded in a single-bond geometry to one C(11) atom. In the seventh H site, H(7) is bonded in a single-bond geometry to one C(12) atom. In the eighth H site, H(8) is bonded in a single-bond geometry to one C(14) atom. In the ninth H site, H(9) is bonded in a single-bond geometry to one C(15) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(16) atom. In the second O site, O(2) is bonded in a single-bond geometry to one C(16) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one C(17) atom. In the fourth O site, O(4) is bonded in a single-bond geometry to one C(17) atom. Linkers: 1 [CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]O[Mg][O].[C][CH].[C][CH].[C][CH].[C][C].[C][C].[C][C].[C][C].[C][C]/C([C]=[CH])=C(\[C])[C]/[C]=[C]\[C].[C][C]=[CH].[C][C][C].[C][C][C]([C])[C].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[Mg].[Mg].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O] ,1 [CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C]/C=[C]\[C]=C/[C].[C]/C=[C]\[C]=C/[C].[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=[CH].[C]=[CH].[C]=[C][CH].[C][CH].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C]=[CH].[C][C][C].[C][C][C].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[Mg].[Mg].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O][C]=O.[O][C]=O.[O][Mg][O] ,1 [CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C]/[C]=[C]\[CH][C].[C]/[C]=[C]\[C].[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C]/[C]=[C]\[C].[C][C]=[CH].[C][C][C].[C][C][C].[C][C][C].[C][C]c1ccc(C([O])=O)cc1.[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[Mg].[Mg].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O] ,1 [CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH]=[C][C]/C=C\[C][C]=O.[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C]/[C]=[C]\C=[C].[C]/[C]=[C]\[C].[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C][CH].[C][CH].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C]/[C]=C(\[C])c1ccc(C([O])=O)cc1.[C][C][C].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[Mg].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O][C]=O.[O][C]O[Mg] ,1 [CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[CH].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C].[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=O.[C]=[CH].[C][CH].[C][CH].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C].[C][C]=O.[C][C][C].[C][C][C].[C][C][C].[C][C][C]=[C].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[H].[Mg].[Mg].[Mg].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O].[O][C]=O.[c]1[c][c][c][c][c]1. Metal clusters: 1 [O][C]=O.[O][C]=O.[O][C]O[Mg]O[C][O]. The MOF has largest included sphere 9.88 A, density 0.76 g/cm3, surface area 5050.35 m2/g, accessible volume 0.80 cm3/g