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

The ellipsoidal clathrate (containing benzene)1B and hemihydrate 1W crystal structure forms of 2,7-dimethyltricyclo[4.3.1.13,8]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)A, 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)A, 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.