Guest exchange dynamics in a flexible bilayer porous coordination polymer

A novel Cd(II)-organic framework [Cd(bpdc)(bpy)⋅DMF] (1) (H2bpdc = biphenyl-3,4′-dicarboxylic acid, bpy = 4,4′-bipyridine) has been synthesized by the solvothermal reaction of Cd2 + salt with H2bpdc and bpy in N,N-Dimethylformamide (DMF) solvent. Single crystal X-ray diffraction revealed that 1 has a two-dimensional (2D) bilayer structure, and the bilayers of 1 are further mutually interdigitated to form a 3D microporous framework. Guest exchange experiments for 1 with several organic solvents and water were performed, and the results display that ethanol can exchange with the guest DMF molecules in 1, but methanol, acetonitrile and water solvents can only induce 1 to extract its guest DMF molecules. Powder X-ray diffraction shows that 1 undergoes a small framework slip between the adjacent interdigitated bilayers triggered by the guest exchange, and the original framework can be restored after the exchanged samples soaked back in the DMF solvent, which demonstrated that 1 has dynamic and flexible interdigitated bilayer motif. The photoluminescent characterization shows that 1 displays blue-green emission in the solid state at room temperature.