Adaptive crystals of homothiacalix[4]arene capable of molecular recognition, with preferential uptake of benzene over cyclohexane

Unique responsive and selective behaviour of homothiacalix[4]arene crystals is reported. A benzene disolvate adopting the <i>1,3-alternate</i> conformation (HTCA-s_1,3) can be converted to a guest-free non-porous phase (HTCA-a_1,3) upon heating, with the host molecules retaining the same <i>1,3-alternate</i> conformation. The process is reversible, with non-porous apohost crystals 'opening up' upon exposure to benzene vapour to reaccommodate the solvent molecules, as confirmed by SCXRD and sorption studies monitored <i>in situ via</i> PXRD analysis. The gate opening mechanism is selective, preventing cyclohexane molecules from passing through, which creates the opportunity to apply this system, for example, in benzene capture/separation. Furthermore, with a higher energy boost, the crystal of the HTCA-a_1,3 apohost undergoes a significant conformational change, resulting in HTCA-a_1,2, an apohost in which the host molecules adopt the <i>1,2-alternate</i> conformation.