Syntheses and crystal structures of four alicyclic diols which crystallise in different lattices involving helical extensions

Abstract

In an exploration of the possibility of modifying the shape and size of the helical canal host structure known to occur in crystals of several bi- and tri-cyclic diols, we report the syntheses and structures of four further diols: 4,8-dimethyl-2-thiatricyclo[3.3.1.1^3,7]decane-syn-4,syn-8-diol 5; 4,8-dimethyl-2-thiatricyclo[3.3.1.1^3,7]decane-syn-4,anti-8-diol 6; 2,7-dimethyltricyclo[4.3.1.1^3,8]undecane-syn-2,anti-7-diol 7; and 2,8-dimethyltricyclo[5.3.1.1^{3 9}]dodecane-anti-2,anti-8-diol 8. All four comprise a class of diols with crystal structures involving hydrogen bonded helices, and all but 7 are resolved into conglomerates on crystallisation. Diols 5 and 6 form closely-related helical columns in space group P4₁ and P4₃ respectively, with only van der Waals attractions between adjacent columns. These structures also involve intramolecular S ⋯ H–O hydrogen bonds giving five-membered cycles which persist in solution. Diol 7 crystallises in space group Pna2₁ with a three-dimensional hydrogen bonded structure involving recurved spirals with a 4-fold diol repeat. The final diol 8 crystallises in space group P3₁21 as a further member of the helical tubuland canal structural family, but with void spaces insufficient for inclusion of guest molecules. The structures are discussed with respect to crystal engineering aspects of synthesis.