The Idiosyncrasies of Tetrabenzo[24]crown-8 in the Solid State

In the solid state, the macrocyclic polyether, tetrabenzo[24]crown-8 (TB24C8), is an interesting molecule. When crystallized from MeCN solution, a bis-MeCN clathrate is formed, in which the TB24C8 macroring—by adopting a conformation with approximate tennis-ball-seam symmetry (D2d)—forms C–H⋯π-linked supramolecular chains. However, when crystallized from CHCl3/Et2O solution, the TB24C8 crystallizes alone—adopting a self-filling ‘flattened-out’ conformation with Ci symmetry—forming C–H⋯π-linked sheets which stack upon one another by virtue of—yet again (!)—C–H⋯π hydrogen bonds. By contrast, the solid-state superstructure of the [2]pseudorotaxane formed between TB24C8 and dibenzylammonium hexafluorophosphate (DBA·PF6), contains no C–H⋯π interactions. However, a multitude of more enthalpically favorable C–H⋯F hydrogen bonds—to a highly-ordered matrix of PF6− anions—stabilizes the formation of the [2]pseudorotaxane array.