A series of five zeolitic imidazolate frameworks (ZIFs) have been synthesized using zinc(II) acetate and five different 4,5-functionalized imidazole units, namely ZIF-25, -71, -93, -96, and -97. These 3-D porous frameworks have the same underlying topology (RHO) with Brunauer-Emmet-Teller surface areas ranging from 564 to 1110 m(2)/g. The only variation in structure arises from the functional groups that are directed into the pores of these materials, which include -CH(3), -OH, -Cl, -CN, -CHO, and -NH(2); therefore these 3-D frameworks are ideal for the study of the effect of functionality on CO(2) uptake. Experimental results show CO(2) uptake at approximately 800 Torr and 298 K ranging from 0.65 mmol g(-1) in ZIF-71 to 2.18 mmol g(-1) in ZIF-96. Molecular modeling calculations reproduce the pronounced dependence of the equilibrium adsorption on functionalization and suggest that polarizability and symmetry of the functionalization on the imidazolate are key factors leading to high CO(2) uptake.

We report CO2 adsorption data for four zeolitic imidazolate frameworks (ZIFs) to 55 bar, namely ZIF-7, ZIF-11, ZIF-93, and ZIF-94. Modification of synthetic conditions allows access to different topologies with the same metal ion and organic link: ZIF-7 (ZIF-94) having sod topology and ZIF-11 (ZIF-93) having the rho topology. The varying topology, with fixed metal ion and imidazolate functionality, makes these systems ideal for studying the effect of topology on gas adsorption in ZIFs. The experiments show that the topologies with the smaller pores (ZIF-7 and 94) have larger adsorptions than their counterparts (ZIF-11 and 93, respectively) at low pressures (<1 bar); however, the reverse is true at higher pressures where the larger-pore structures have significantly higher adsorption. Molecular modeling and heat of adsorption measurements indicate that while the binding potential wells for the smaller-pore structures are deeper than those of the larger-pore structures, they are relatively narrow and cannot accommodate multiple CO2 occupancy, in contrast to the much broader potential wells seen in the larger pore structures.