A comparison of the crystal packing in benzene with the geometry seen in crystalline cyclophane-benzene complexes: guidelines for rational receptor design

Abstract

Self-recognition in crystalline benzene is compared with the recognition of benzene in inclusion complexes of three cyclophane receptors. It is shown that the structural organization of aromatic rings, which determines the packing in the molecular crystal and the binding geometry in the preorganized cavity of the cyclophane host molecules, follows the same principles. It is concluded that the examination of the spatial requirements of the aromatic-aromatic interaction motifs found in crystals should allow one to design host bonding skeletons with high binding selectivity and affinity for a specific aromatic guest.

Substituent Effects on the Stability of Arene−Arene Complexes: An AM1 Study of the Conformational Equilibria ofcis-1,3-Diphenylcyclohexanes

“…Although coplanar (or displaced coplanar) arene rings are found in many arene complexes, in a number of cases, the lowest energy form of arene complexes is not a π-stacked but rather an edge-to-face, or “T-shaped”, complex. ,− In order to assess the energetic preference of the two phenyl rings in 1 − 3 to adopt either a π-stacked or edge-to-face orientation, energy profiles were calculated for 1 and 3 (X, Y = H) as a function of the torsional angle τ, which is defined by C-6, C-1, C-1‘, and C-2‘. The profile calculated for 1 shows two pairs of symmetry-related minima, one corresponding to the π-stacked orientation at τ = 0° and 180° and the other to an edge-to-face orientation at τ = 90° and 270° (Figure ).…”

Conformation of Acyclic Derivatives of 1,1,4,4-Tetraphenyl-1,3-butadiene

“…This indicates that rotation of the bulky substituents about the ==C---C~ bond is sterically hindered, which introduces features of 'soft' chirality into the molecular structure (in solution the molecules equilibrate rapidly between inverted configurations). It also suggests that favourable aryl-aryl 7r-Tr interactions between the overlapping rings contribute significantly to the stabilization of the observed conformation (Klebe & Diederich, 1993;Burley & Petsko, 1986). Variation of packing forces in the crystal structures of (I)-(III) and the presence of extensive intermolecular hydrogen bonding in the ethanol solvate of (II) seem to have little effect on the molecular conformation of the title entity.…”

Molecular Recognition in Organic Crystals: Directed Intermolecular Bonds or Nonlocalized Bonding?

“…Thus, the A, B, and C nearestneighbor pairs have been used as a basis for designing molecules with special affinity for specific aromatic guests. [50] The computational results inform us about how a given molecule in the benzene crystal structure interacts with its neighbors but they do not explain why benzene adopts the particular crystal structure that it does and not some other structure. Indeed, the main lesson to be drawn is that the observed benzene crystal structure depends on a subtle balance of long-range, cooperative effects, and that to describe it as being driven by favorable contacts between positively charged H atoms and negatively charged C atoms is a vast oversimplification.…”