Impact of intermolecular packing on separation of chlorinated cyclic hydrocarbons using flexible hydrogen-bonded organic frameworks

Abstract

A nonplanar phenothiazine derivative (PTTCN) was synthesized to construct adsorption hydrogen-bonded organic frameworks for separation of chlorinated cyclic hydrocarbons, chlorobenzene (ClBz) and chlorocyclohexane (ClCy). PTTCN can form two distinct organic frameworks in ClBz and ClCy through intermolecular hydrogen bonding. These frameworks exhibit different fluorescence colors, which can be attributed to variations in molecular conformations and packing patterns. Upon heating, both frameworks are capable of releasing the guests; however, their separation performances towards the ClBz/ClCy mixture differ significantly. Specifically, X-HOF-6a derived from ClBz selectively reabsorbs ClBz from the equimolar mixture accompanying a gate-opening process and a small change in intermolecular arrangement, resulting in a purity of 99.4%. Moreover, X-HOF-6a demonstrates excellent reusability. On the other hand, the intermolecular stacking type in X-HOF-7a derived from ClCy is very different from those in X-HOF-a and X-HOF-7, and then X-HOF-7a exhibits non-selective adsorption by capturing both ClCy and ClBz molecules simultaneously. The investigations suggest that selectivity is determined by the extent of alteration in intermolecular stacking upon guest adsorption, with higher selectivity observed for smaller changes.