Assembly of two porous cadmium(II) frameworks: Selective adsorption and luminescent property

摘要

Two microporous cadmium(II) metal-organic frameworks, [Cd(cptpy)(Ac)(H _2O)(DMA)(H _2O)] _n (1) and [Cd(cptpy) _2(DMF) _2] _n (2) (Hcptpy = 4-(4-carboxyphenyl)-2, 2′:4′,4′-terpyridine, DMA = N,N-dimethylacetamide, DMF = dimethylformamide) have been solvothermally synthesized under different reaction conditions. Complex 1 is a double-interpenetrating 3D network, while 2 is a noninterpenetrating (3,5)-connected 2D framework. The dehydrated forms of compounds 1 and 2 exhibit selective adsorption of CO _2 over N _2 and H _2O over CH _3OH. In addition, the adsorption value of CO _2 for 2 is higher than that of 1. The contents of uncoordinated pyridine nitrogen (Lewis basic sites) per formula unit of 1 and 2 are 2.16 and 4.36%, respectively. Obviously, the grafting of more uncoordinated pyridine nitrogen into compound 2 could enhance adsorption of the acidic CO _2 molecule. Notably, both 1 and 2 display strong photoluminescence. The nature of electronic transitions for complex 1 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.