Direct Guest Exchange Induced Single-Crystal to Single-Crystal Transformation Accompanying Irreversible Crystal Expansion in Soft Porous Coordination Polymers

Two flexible porous coordination materials, [Mn(pybimc)₂]·2H₂O·G (G = toluene, 1_tol; THF, 1_thf), where pybimc = 2-(2′-pyridyl)-benzimidazole-5-carboxylate, featuring identical one-dimensional chain structure have been characterized. Guest exchange studies have exhibited that 1_tol cannot be converted to 1_thf through direct replacement of guest toluene molecules by THF molecules, but, of particular interest, 1_thf is actually converted to 1_tol and 1_aromatic (where aromatic = o-, m-, p-xylene) upon the exchange of THF to toluene and other aromatic molecules, respectively. This signifies a single-crystal to single-crystal transformation accompanied irreversible crystal expansion. In-depth analyses reveal that the nature of the weak yet sufficiently strong framework-guest C-H···π interactions, rather than the guest size, observed in this system plays a key role in guiding the adsorption of liquid-phase aromatics in the soft crystalline materials. (Figure Presented).