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, <b>1</b>_<b>tol</b>; THF, <b>1</b>_<b>thf</b>), where pybimc = 2-(2′-pyridyl)-benzimidazole-5-carboxylate, featuring identical one-dimensional chain structure have been characterized. Guest exchange studies have exhibited that <b>1</b>_<b>tol</b> cannot be converted to <b>1</b>_<b>thf</b> through direct replacement of guest toluene molecules by THF molecules, but, of particular interest, <b>1</b>_<b>thf</b> is actually converted to <b>1</b>_<b>tol</b> and <b>1</b>_{<b>aromatic</b>} (where aromatic = <i>o</i>-, <i>m</i>-, <i>p</i>-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