Understanding the Pseudoflexibility of a Co-btc Coordination Polymer

A new functionalized coordination polymer (CP), [Co₂(DMA)₃(btc)Cl]n (<b>CP 1</b>) was developed starting from 1,3,5-trimesic acid (H₃btc), cobalt chloride, and N,N-dimethylacetamide (DMA). In the presence of moisture, the highly active blue-colored <b>CP 1</b> was transformed into a solid pink-colored CP, [Co₃(btc)₂·12H₂O]_n (<b>CP 2</b>). The structures of <b>CP 1</b> and <b>CP 2</b> were confirmed by single-crystal X-ray diffraction (SCXRD) studies. Remarkably, <b>CP 2</b> can be transformed back into <b>CP 1</b> in the presence of DMA. The drastic reversible structural transformation between <b>CP 1</b> and <b>CP 2</b> involves the breakage and reformation of metal-carboxylate bonds, amendments in the coordination geometry around Co(II) centers, as well as changes in the coordination mode of the btc^3- ligand. A plausible mechanistic study reveals that, instead of a solvent-induced flexible structural transformation between these CPs, <b>CP 1</b> actually degrades to <b>CP 2</b> along with hydrated cobalt chloride. Here, we have shown that even after the degradation of a CP, the CP can be recovered by knowing the proper mechanistic pathway of the reaction. Besides that, a new strategy was developed to make the active and functionalized CP (<b>CP 1</b>) from the stable, well-ordered CP (<b>CP 2</b>). This unique phenomenon of CP transformation can be termed as "pseudoflexibility" of CPs.