Versatile inclusion behaviour of a dinitrocalix[4]arene having two ester pendants -: Preparation and X-ray crystal structures of complexes

An upper-rim dinitro-substituted calix[4]arene possessing two lower-rim ethyl ester pendant groups (1) has been shown to form solid inclusion compounds with acetone (1:1) (1a), DMF (1:1) (1b), DMSO (1:1) (1c) and n-BuOH (2:1) (1d). X-ray crystal structures of the four complexes 1a-d are reported and comparatively discussed, including isostructurality calculations. Although the solid-state conformation of the dinitrocalix[4]arene moiety, stabilized by two intramolecular O-H...O bonds, is maintained in the four inclusion compounds, and all four co-crystals have similar unit cell dimensions and identical space group symmetries, only three of them (1a-c) are homostructural. Depending on the nature of the guest molecule, either the upper or the lower rim site of the calixarene is involved in the complexation, demonstrating either cavitate- or clathrate-type of supramolecular interactions, respectively. Moreover, due to the different guest recognition modes, the calixarene host in 1d is rotated through a non-crystallographic virtual rotation of 180 degrees within the unit cell, in relation to the host molecules in each of the other three homostructural compounds 1a-c, thus giving rise to supramolecular morphotropism - to our knowledge the first case ever described.