2,7-DIMETHYLTRICYCLO[4.3.1.1(3,8)]UNDECANE-SYN-2,SYN-7-DIOL - STRUCTURAL-ANALYSIS OF THE ELLIPOSIDAL CLATHRATE AND HEMIHYDRATE CRYSTAL FORMS

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) angstrom, 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) angstrom, 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.