Disorder versus symmetry in the helical tubuland inclusion host lattice—a successful trishomocubyl diol probe

Abstract

New examples of the helical tubuland diol host family may be targeted for synthesis by consideration of structural rules which result in formation of the specific hydrogen bonding arrangement required. To test crystal engineering requirements of symmetry and substitution in these diols, the 4,7, 11-trimethylpentacyclo[6.3.0.0^2,6.0^3,10,0^5,9]undecane-4,7-diol isomer 8a has been prepared and its X-ray structure determined: [C₁₄H₂₀O₂, P3₁21, a 12.609(2), c 7.209(2)Å, Z 3, R 0.032]. This diol is a further example of the helical tubuland family despite it lacking C₂ symmetry. Instead, overall C₂ symmetry results in the solid state by means of crystallographic disorder. The C11 methyl group which is equally disposed over its two possible positions reduces the canal unobstructed cross-sectional area to only 8.9 Ų, but demonstrates that disruption of the lattice type can be avoided provided substituents are placed within the parallel canals. These observations now allow prediction of a much wider range of helical tubuland structures. The diol isomer 8b[C₁₄H₂₀O₂, P2₁/c, a 12.795(1), b 6.4608(4), c 15.003(1)Å, β 111.846(4)°, Z 4, R 0.043] forms a layer structure involving (–OH)₄ cycles in common with other diols of closely related structure.