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Guest‐Induced Supramolecular Isomerism in Inclusion Complexes of T‐Shaped Host 4,4‐Bis(4′‐hydroxyphenyl)cyclohexanone
Author(s) -
Aitipamula Srinivasulu,
Nangia Ashwini
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500400
Subject(s) - chemistry , phenol , hydrogen bond , supramolecular chemistry , cyclohexanone , crystallography , molecule , phenols , aniline , stereochemistry , organic chemistry , catalysis
The T‐shaped host molecule 4,4‐bis(4′‐hydroxyphenyl)cyclohexanone ( 1 ) has an equatorial phenol group and a cyclohexanone 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 / m ‐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, m ‐cresol, o ‐chlorophenol, and m ‐bromophenol) compared with a size of 10×13 Å for phenol and aniline inclusion. The ladder host framework of 1 is chiral ( P 2 1 ) with phenol, whereas the inclusion of isosteric o ‐ and m ‐fluorophenol results in a novel polar brick‐wall assembly (7×11 Å voids) as a result of auxiliary CH⋅⋅⋅F interactions. The conformational flexibility of strong OH⋅⋅⋅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, CH⋅⋅⋅F interactions) drive the crystallization of T‐host 1 towards 1D 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, 1 H NMR spectroscopy, and thermogravimetry‐infrared (TG‐IR) analysis. The T onset value (140 °C) of aniline in the TGA is higher than those of phenol and the higher‐boiling cresol guests ( T onset =90–110 °C) because the former structure has more OH⋅⋅⋅N/NH⋅⋅⋅O hydrogen bonds than the clathrate of 1 with phenol which has OH⋅⋅⋅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 CH⋅⋅⋅F interactions ( o ‐ and m ‐fluorophenol) can change the molecular arrangement in strongly hydrogen‐bonded crystal structures.