Structure and conformation of the hydrate of 8,11-dihydroxypentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8,11-carbolactam

The crystalline modification of the title compound from aqueous medium depends critically on factors such as concentration and pH. Crystallographic analysis of a hydrated crystal showed that this effect related to the formation of an extended network of hydrogen bonds that requires the water molecule, as H₂O, to be hydrogen bonded three ways. The crystals are monoclinic, C2/c, a = 10.030 (1), b = 9.840 (2), c = 21.625 (2) Å, β = 90.87 (1)°, Z = 8. The hydrogen-bond network between water of hydration and the functional groups on the cage compound has identical geometries for both chiralities and during crystallization there is hence no discrimination between enantiomers. Both forms are thus accommodated at the same sites in random distribution, causing disorder of the molecular fragment remote from the functional region. The final arrangement is similar to a hydrated solid solution of the two enantiomers with an IR spectrum sufficiently different from the anhydrous form to suggest a different molecular arrangement.

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