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)]center dot H2O}(n) (1) and {[Cu-4(L)(2)(H2O)(4)]center dot 4DMF center dot 8H(2)O}(n) (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, {[Cu-4(L)(2)(ATZ)(2)(H2O)]center dot 5DMF center dot 5H(2)O}(n) (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.