Two new zinc MOFs with similar "pillar-layered" framework structures based on 1,1'-biphenyl-2,2',6,6'-tetracarboxylic acid (H(4)bpta) and two different bipyridine pillar ligands, namely {[Zn-4(bpta)(2)(4-pna)(2)(H2O)(2)] center dot 4DMF center dot 3H(2)O (1) and {[Zn-2(bpta)(bpy-ea)-(H2O)]center dot 2DMF center dot H2O} (2) (4-pna = N-(4-pyridyl)isonicotinamide and bpy-ea = 1,2-bis(4-pyridyl)ethane), have been synthesized and investigated with their CO2 adsorption properties. By analysis of the structure properties and the CO2 adsorption performances of these two MOFs, it was found that the introduction of polar acylamide groups via 4-pna resulted in 1 with enhanced CO2 capacity and CO2/CH4 selectivity at low pressure. In contrast, the framework of 2 shows flexible properties originating from the flexibility of the ethanediylidene group in the bpy-ea ligand, which benefits the sieve effect of pores to give higher CO2/CH4 selectivity at a relatively high pressure range.