Supramolecular crystalline construction based on a mandelic acid source. Host design, inclusion formation and X-ray crystal structures of a methanol inclusion complex and free host structures in racemic and optically resolved forms

Abstract

A new host compound in optically resolved and racemic forms for selective crystalline inclusion formation derived from natural mandelic acid was synthesized. Inclusion properties of the two optical species are discussed, involving comparison with a lactic acid-based host analogue. Inclusion compounds with amines, ketones and heterocyclics and specifically with small unbranched alcohols were isolated. The crystal and molecular structures of the optically resolved and racemic forms of the free host at room temperature and the methanol inclusion complex of the resolved host at 255 K were determined by x-ray analysis. Two different binding schemes characterize the packing of these structures, in which one hydroxyl group is responsible for the formation of dimers and chains while in the free host the other hydroxyl group is involved in OH···phenyl interactions. A survey of the OH ···phenyl interactions based on the Cambridge Structural Data Base (October 1994 version) reveals that π-electron bonding occurs in a wide range of crystal structures. The approximation of the hydrogen appears to take place in an asymmetric way. Several calculations for the ab initio prediction of the crystal structures were performed.