The idiosyncrasies of tetrabenzo[24]crown-8 in the solid state

In the solid state, the macrocyclic polyether, tetrabenzo[24]crown-8 (TB24C 8), is an interesting molecule. When crystallized from MeCN solution, a bis -MeCN clathrate is formed, in which the TB24C8 macroring-by adopting a conf ormation with approximate tennis-ball-seam symmetry (D-2d)-forms C-H...pi-l inked supramolecular chains. However, when crystallized from CHCl3/Et2O sol ution, the TB24C8 crystallizes alone-adopting a self-filling 'flattened-out ' conformation with Ci symmetry-forming C-H...pi-linked sheets which stack upon one another by virtue of-yet again (!)-C-H...pi hydrogen bonds. By con trast, the solid-state superstructure of the [2]pseudorotaxane formed betwe en TB24C8 and dibenzylammonium hexafluorophosphate (DBA-PF6), contains no C -H...pi 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 Lt d. All rights reserved.