Guest-Induced Phase Switching in a Square Lattice Coordination Network to Enable Selective Adsorption of p-Xylene

Flexible coordination networks (CNs) offer the potential for exceptional selectivity to enable hydrocarbon separations. The key to performance in such sorbents is guest-induced structural transformations that result in induced-fit binding. Unfortunately, the underlying mechanisms of such transformations remain largely unexplored. Herein, we report an investigation of the phase switching behavior of the square lattice (sql) CN [Cu(4,4'-bipyridine)₂(CF₃CO₂)₂]_n (sql-1-Cu-CF₃CO₂) induced by xylene adsorption. Competitive adsorption studies in binary and ternary xylene mixtures revealed high p-xylene (PX) selectivity of 10.83 over o-xylene (OX) and of 14.18 over m-xylene (MX), with an overall PX selectivity of 10.01, surpassing most commercial sorbents such as zeolites. Crystallographic studies revealed three distinct xylene-loaded phases with varying pore/channel dimensions and porosity: 1D (void: 33.9%) for PX, 2D (void: 45.8%) for OX, and 3D (void: 48.4%) for MX. The PX-loaded structure exhibited the smallest void but the strongest host-guest interactions, making it the preferred phase for PX separation from xylene mixtures.