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)]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 CO2 over N2 and H2O over CH3OH. In addition, the adsorption value
of CO2 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 CO2 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.