Comparative X-ray structural study of laterally mono-ethyl substituted 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra-methoxycalix[4]arene and its non-substituted parent compound including guest free and solvated forms. Chemical straightening of guest channels

Three solvate crystal structures of the laterally ethyl substituted tetra-tert-butyltetramethoxycalix[4]arene 1 [(1·THF (1a), 1·CHCl3 (1b) and 1·CH2Cl2 (1c)] are compared to the corresponding solvent-free structure (1) using single crystal X-ray structure determination, isostructurality and molecular isometricity calculations. To study the effect of the lateral substitution, the laterally non-substituted host with the guest THF (2a) is also included to the comparison. The calixarene molecules in the different structures all adopt the partial cone conformation with different affection of the respective guest molecules, always being positioned interstitially. Depending on the lateral substitution and the size of the included guests, the molecular conformation of the calix[4]arene shows small differences relating to the alignment of the arene units. The channels disposable of the solvent guest molecules in the crystal structures straighten as the effect of lateral substitution of the host calix[4]arene. The orthorhombic crystal structures of 1a–c are isostructural irrespective of the included solvent molecules, while 1 and 2a crystallise in the same monoclinic space group.