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RESEARCH PRODUCT

Insight into the Mechanism of Water Adsorption/Desorption in Hydrophilic Viologen-Carboxylate Based PCP

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A water stable and highly hydrophilic porous coordination polymer based on viologen-carboxylate type ligand, the 4,4′-bipyridinium,1,1-bis(3-carboxyphenyl) (pc2), is obtained by the solvothermal method: [Cd3(pc2) (BTC)2(H2O)2]·6H2O ([1(H2O)2]·6H2O; BTC3– = 1,3,5-carboxybenzene). Its crystal structure and the ones of two partially dehydrated phases have been determined, allowing insight into the mechanism of water adsorption/desorption of this PCP material. It is shown that the dehydrated compound [1] first adsorbs two water molecules which fill the pores, leading to [1]·2H2O. On the other hand, the partial dehydration of the as-synthesized compound leads to the intermediate phase [1(H2O)]·3H2O in which one H2O molecule is bound to Cd2+ ions of trinuclear building units, and three others are localized in the pores. The structural analysis also reveals that the pyridinium N+ Lewis sites, which interact with water molecules in [1(H2O)2]·6H2O, interact with carboxylate groups after structural reorganization i...