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

本研究对两种柔性多孔配位材料[Mn(pybimc)₂]·2H₂O·G（G分别为甲苯（toluene，记为1tol）、四氢呋喃（THF，记为1thf），其中pybimc=2-(2'-吡啶基)苯并咪唑-5-羧酸根）进行了表征，二者具有完全一致的一维链状结构。客体交换实验结果显示，1tol无法通过直接将客体甲苯替换为四氢呋喃分子转化为1thf；而尤为值得关注的是，1thf分别与甲苯、其他芳香族分子进行客体交换后，可转化为1tol与1aromatic（其中aromatic指代邻、间、对二甲苯）。该过程伴随单晶到单晶转变与不可逆的晶体膨胀。深入分析表明，本体系中观测到的弱但强度足够的框架-客体C-H···π相互作用，而非客体尺寸，在指导软晶材料液相芳烃吸附的过程中起到了关键调控作用。