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

The T-shaped host molecule 4,4-bis(4'-hydroxyphenyl)cyclohexa-none (1) has an equatorial phenol group and a cyclohexanone group along the arms and an axial phenol ring as the stem. ne equatorial phenyl ring adopts a "shut" or "open" conformation, like a windowpane, depending on the size of the guest (phenol or o/m-cresol), for the rectangular voids of the hydrogen-bonded ladder host framework. The adaptable cavity of host 1 expands to 11 x 15-18 angstrom through the inclusion of water with the larger cresol and halophenol guests (o-cresol, m-cresol, o-chlorophenot, and m-bromophenol) compared with a size of 10 x 13 angstrom for phenol and aniline inclusion. The ladder host framework of 1 is chiral (P2(1)) with phenol, whereas the inclusion of isosteric o- and m-fluorophenol results in a novel polar brick-wall assembly (7 x 11 angstrom voids) as a result of auxiliary C-(HF)-F-... interactions. The conformational flexibility of strong O-(HO)-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 1D ladder and 2D brick-wall structures, that is, supramolecular isomerism. Host I exhibits selectivity for the inclusion of aniline in preference to phenol as confirmed by X-ray diffraction, H-1 NMR spectroscopy, and thermogravimetry-infrared (TG-IR) analysis. The T-onset value (140 degrees C) of aniline in the TGA is higher than those of phenol and the higher-boiling cresol guests (T-onset = 90-110 degrees C) because the former structure has more O-(HN)-N-.../N-(HO)-O-... hydrogen bonds than the clathrate of 1 with phenol which has O-(HO)-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 I 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.