Structural Tuning and Pore Modulation of Three Cu(II)-Organic Frameworks: Enhancement of Stability and Functionality

Through use of an irregular pentacarboxylate ligand, 2,2'-(pyridine-2,6-diyl)diterephthalic acid (H₄L), two Cu(II)-based metal-organic frameworks, {[(Me₂NH₂)_0.5][Cu_0.75(L)_0.5(DMA)_0.375]·H₂O} (1) and {[Cu₄(L)₂(H₂O)₄]·4DMF·8H₂O} (2), have been synthesized. A structural analysis demonstrates that 1 is a 2D layer and 2 shows a 3D framework, which exhibit hopeful possibilities for the selective separations of C₂H₂/CH₄ and CO₂/CH₄. To enhance the adsorption properties, 5-amino-1H-tetrazole (HAT) has been introduced in the synthesis system, and a new framework, {[Cu₄(L)₂(ATZ)₂(H₂O)]·5DMF·5H₂O} (3), has been obtained. 3 is a 3D framework. Especially, 3 is constructed from multiple SBUs and displays an unusual (3,4,6)-connected topology. Furthermore, especially 3 performs better than 1 and 2 in terms of uptake capacity as well as adsorption selectivity, which might be ascribed to the more proper pore space of 3.