Understanding the Pseudoflexibility of a Co-btc Coordination Polymer

A new functionalized coordination polymer (CP), [Co 2 (DMA) 3 (btc)Cl]n ( CP 1 ) was developed starting from 1,3,5-trimesic acid (H 3 btc), cobalt chloride, and N,N-dimethylacetamide (DMA). In the presence of moisture, the highly active blue-colored CP 1 was transformed into a solid pink-colored CP, [Co 3 (btc) 2 ·12H 2 O] n ( CP 2 ). The structures of CP 1 and CP 2 were confirmed by single-crystal X-ray diffraction (SCXRD) studies. Remarkably, CP 2 can be transformed back into CP 1 in the presence of DMA. The drastic reversible structural transformation between CP 1 and CP 2 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, CP 1 actually degrades to CP 2 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 ( CP 1 ) from the stable, well-ordered CP ( CP 2 ). This unique phenomenon of CP transformation can be termed as “pseudoflexibility” of CPs.