Guest-induced supramolecular isomerism in inclusion complexes of T-shaped host 4,4-bis(4′-hydroxyphenyl)cyclohexanone

Abstract

The T-shaped host molecule 4,4-bis(4′-hydroxyphenyl)cyclohexanone (1) has an equatorial phenol group and a cyclohexanonc group along the arms and an axial phenol ring as the stem. The equatorial phenyl ring adopts a "shut" or "open" conformation, like a windowpane, depending on the size of the guest (phenol or o/w-cresol), for the rectangular voids of the hydrogen-bonded ladder host framework. The adaptable cavity of host 1 expands to 11 × 15-18 Å through the inclusion of water with the larger cresol and halophenol guests (o-cresol, wz-cresol, o-chlorophenol, and w-bromophenol) compared with a size of 10×13 Å for phenol and aniline inclusion. The ladder host framework of 1 is chiral (P21) with phenol, whereas the inclusion of isosteric o- and w-fluorophenol results in a novel polar brick-wall assembly (7×11 Å voids) as a result of auxiliary C-H⋯F interactions. The conformational flexibility of strong O-H⋯O hydrogen-bonding groups (host 1, phenol guest), the role of guest size (phenol versus cresol), and weak but specific intermolecular interactions (herringbone T-motif, C-H⋯F interactions) drive the crystallization of T-host 1 towards 1 D ladder and 2D brick-wall structures, that is, supramolecular isomerism. Host 1 exhibits selectivity for the inclusion of aniline in preference to phenol as confirmed by X-ray diffraction, 1H NMR spectroscopy, and thermogravimetry-infrared (TG-IR) analysis. The Tonset value (140°C) of aniline in the TGA is higher than those of phenol and the higher-boiling cresol guests (Tonset = 90-110°C) because the former structure has more O-H⋯N/N-H⋯O hydrogen bonds than the clathrate of 1 with phenol which has O-H⋯O hydrogen bonds. Guest-binding selectivity for same-sized phenol/aniline molecules as a result of differences in hydrogen-bonding motifs is a notable property of host 1. Host-guest clathrates of 1 provide an example of spontaneous chirality evolution during crystallization and a two-in-one host-guest crystal (phenol and aniline), and show how weak C-H-F interactions (o- and m-fluorophenol) can change the molecular arrangement in strongly hydrogen-bonded crystal structures. © 2005 Wiley-VCH Verlag GmbH & Ca KGaA, Weinheim.