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 tenms-ball-seam symmetry (D(2d)) - 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 C(i) 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. (C) 2000 Elsevier Science Ltd.