Abstract
The solid-state structures of the complexes of calix[4]arenediphosphonic acid with piroxicam and 9-aminoacridine are described, in both cases, the classical interdigitated dimer formed by calix[4]arenediphosphonic acid is no longer present. For the 9-aminoacridine complex, a π–π stacked dimer of 9-aminoacridine is surrounded by calix[4]arenediphosphonic acid molecules with dimethyl sulfoxide included in the calix arene cavity. In the case of the piroxicam complex the piroxicam molecule forms a true inclusion complex and the pyridinium ring projects out to hydrogen bond to an opposing calix[4]arenediphosphonic acid, thus spanning the bilayer.
Graphical Abstract
The structures of the complexes of calix[4]arenediphosphonic acid with piroxicam and 9-aminoacridine show a breakdown in the classical interdigated calix-arene dimer with formation of trus inclusion complexes and exo-complexation.