Assembly of Two Porous Cadmium(II) Frameworks: Selective Adsorption and Luminescent Property

Two microporous cadmium­(II) metal–organic frameworks, [Cd­(cptpy)­(Ac)­(H₂O)·(DMA)­(H₂O)]_<i>n</i> (<b>1</b>) and [Cd­(cptpy)₂·(DMF)₂]_<i>n</i> (<b>2</b>) (Hcptpy = 4-(4-carboxyphenyl)-2,2′:4′,4″-terpyridine, DMA = <i>N</i>,<i>N</i>-dimethylacetamide, DMF = dimethylformamide) have been solvothermally synthesized under different reaction conditions. Complex <b>1</b> is a double-interpenetrating 3D network, while <b>2</b> is a noninterpenetrating (3,5)-connected 2D framework. The dehydrated forms of compounds <b>1</b> and <b>2</b> exhibit selective adsorption of CO₂ over N₂ and H₂O over CH₃OH. In addition, the adsorption value of CO₂ for <b>2</b> is higher than that of <b>1.</b> The contents of uncoordinated pyridine nitrogen (Lewis basic sites) per formula unit of <b>1</b> and <b>2</b> are 2.16 and 4.36%, respectively. Obviously, the grafting of more uncoordinated pyridine nitrogen into compound <b>2</b> could enhance adsorption of the acidic CO₂ molecule. Notably, both <b>1</b> and <b>2</b> display strong photoluminescence. The nature of electronic transitions for complex <b>1</b> in the photoluminescent process was investigated by means of time-dependent density functional theory (TDDFT) calculations and molecular orbital analyses, which collaborates that the luminescent property is ligand-based