The crystal and molecular structures of bridged spherands: The host C₅₂H₅₂O₈, its complex C₅₂H₅₂O₈·Li⁺, and the complexes C₅₀H₄₈O₆·Li⁺ and C₅₂H₅₂O₆·Li⁺

Abstract

The structures of the title novel hosts and host-guest complexes, synthesized by D. J. Cram and his colleagues, were determined by direct methods from diffractometer data and refined by least-squares. The hosts C₅₂H₅₂O₈,I, C₅₀H₄₈O₆,II, and C₅₂H₅₂O₆,III, are di-bridged derivatives of the prototype spherand C₄₈H₄₈O₆,IV. InIV, six 4-methylanisole units are joined in the 2,6 positions. InI two -CH₂CH₂OCH₂CH₂- bridges replace four of the methoxy methyl groups, joining pseudo-meta oxygen atoms; these two bridges are on the same face of the macrocycle (syn). InII andIII, trimethylene and tetramethylene bridges, respectively, are similarly situated, again replacing four methoxy methyls ofIV. CompoundsIa,IIa andIIIa are Li⁺ complexes of these hosts. The lithium ion is essentially hepta-coordinated inIa, penta-coordinated inIIa and hexa-coordinated inIIIa. These structures are extremely rigid, and the aromatic rings in them are greatly deformed. There are intramolecular oxygen contacts in each complex only slightly greater than 2.5 Å, about 10 percent shorter than the sum of the usual van der Waals radii for oxygen atoms. Thus the structures provide useful data for parameterizing potential functions for molecular mechanics calculations.