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Direct Crystallographic Observation of Catalytic Reactions inside the Pores of a Flexible Coordination Polymer

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Abstract

A new flexible porous coordination polymer (PCP), {[Gd2(L)3(dmf)4]4 DMF3 H2O}n (1), was synthesized under solvothermal condition by reacting [Gd(NO3)3]6 H2O with the ligand 2,6,2′,6′-tetranitro-biphenyl-4,4′-dicarboxylic acid (H2L). Compound 1 had a 3D coordination polymeric structure with two types of 1D channels (A and B) that were occupied by DMF and water molecules. When crystals of 1 were separately exposed to vapors of various aromatic aldehydes, either the lattice or both the lattice and metal-bound solvent molecules were replaced by aldehyde molecules. The aldehyde molecules inside the pores spontaneously underwent cyanosilylation and Knoevenagel condensation reactions upon exposure to vapors of trimethylsilyl cyanide and malononitrile, respectively. These reactions took place at ambient temperature and pressure. Moreover, both the reactants and the products translocated from one cavity to another. The products that occupied the cavity were expunged upon exposure to the vapors of an aldehyde. Because crystallinity was maintained during these chemical transformations, direct crystallographic observation was possible. Herein, we showed that confinement of the reactants inside the void spaces of the PCP led to the products; we also assessed catalytic activities of this PCP in bulk quantities.

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