Pseudopolymorphic Clathrate Structures Formed by an Alicyclic Dialcohol Inclusion Host

Dialcohol host 2,7-dimethyltricyclo[4.3.1.0^3,8]undecane-syn-2,syn-7-diol 1 can form either ellipsoidal clathrate or helical tubulate inclusion compounds where only dispersion forces operate between the hosts and guests. The former (tetragonal space group I4₁/acd), built from two interpenetrating sublattices containing both diol enantiomers, encloses the guests in rugby ball-shaped cavities. The latter (trigonal space group P3₁21 or P3₂21), containing only one diol enantiomer, traps the guests within parallel tubes. Which inclusion type is produced is determined by the guest size and shape and, hence, control is possible over these structures. At room temperature, cyclohexane gives the tetragonal structure, but fluorocyclohexane yields the trigonal structure. Chloroform produces both pseudopolymorphs: the tetragonal form at higher and the trigonal form at lower temperatures. Powder and single-crystal structural X-ray data are reported for these clathrate compounds.