Aromatic guest-induced layer expansion and phase switching in a 2D square lattice coordination network

Switching coordination networks (CNs) that exhibit guest-induced phase transformations hold promise for molecular recognition and separation, yet their responsiveness to different adsorbates remains underexplored. Herein, we further investigate the previously reported guest-induced layer expansion and phase switching behavior of a 2D square lattice (sql) topology CN, [Co(4,4′-bipyridine)₂(NCS)₂]_n (sql-1-Co-NCS), in the presence of a new group of aromatic guests, methylbenzene (MB), nitrobenzene (NB), and 1,3,5-trimethylbenzene (TMB). Overall, aromatic guest-induced open phases can be classified into three categories based on the number of guest molecules accommodated per formula unit, H·xG (x = 2, 3, 4), with interlayer distances spanning 5.92–9.61 Å. The TMB-loaded phase is unusual as it exhibits an alternating layered arrangement with two distinct interlayer distances of 8.29 and 8.80 Å. Vapor adsorption studies of sql-1-Co-NCS revealed that MB vapor triggers phase switching at a lower relative pressure than C₈ aromatics, indicating a stronger host framework response and highlighting the potential of this material for the separation of substituted benzene derivatives.