2,7-Dimethyltricyclo[4.3.1.13,8]undecane-syn-2,syn-7-diol: structural analysis of the ellipsoidal clathrate and hemihydrate crystal forms

Abstract

The ellipsoidal clathrate (containing benzene)1B and hemihydrate 1W crystal structure forms of 2,7-dimethyltricyclo[4.3.1.1^3,8]undecane-syn-2,syn-7-diol determined by X-ray crystallography are described and contrasted with the previously reported solvent-free 1 and helical tubulate (containing ethyl acetate)1E structures. The superlattice comprising structure 1B[(C₁₃H₂₂O₂)₄·(C₆H₆)I4₁/acd, a,b 23.021(1), c 18.889(2)Å, Z 8, R 0.035] is assembled from two identical interpenetrating sublattices which are inversion related. Each of these is constructed from a three-dimensional network of hydrogen bonded diol molecules. Benzene guests occupy D₂ sites in ellipsoidal cavities between neighbouring sublattices. The hemihydrate structure 1W[(C₁₃H₂₂O₂)₂·(H₂O). Pbca, a 13.4829(6), b 13.6657(5), c 26.4388(9)Å, Z 8, R 0.051] involves diol and water molecules hydrogen bonded together in a spirocyclic manner to create a layer structure. Reasons for formation of the alternative structures in particular circumstances are discussed.