Abstract
A new three-dimensional (3D) bi-porous metal-organic framework (MOF), {[(Me2NH2)(2)]center dot[Cd-3(5-tbip)(4)]center dot 2DMF}(n) (1) (5-tbipH(2): 5-tert-butylisophthalic acid) has been synthesized. The 5-tbip ligand containing a hydrophobic t-butyl group and hydrophilic carboxylate groups is used to synthesize the bi-porous framework. This 3D MOF contains two types of channels, a wide mouth hydrophilic channel of dimension 7.448 x 7.676 angstrom(2) and a narrow mouth hydrophobic channel of dimension 2.33 x 1.926 angstrom(2). Hydrophilic channels are lined with the orderly arranged dimethyl ammonium (DMA) cations which neutralize the anionic 3D framework. The guest-free form of the MOF (1 ') showed interesting CO2 selectivity over other gases such as N-2, CH4, and H-2. Since the effective pore size of the desolvated compound 1 ' (similar to 0.6 nm: from the pore size distribution curve of CO2 adsorption measurement) is much more than the kinetic diameter of all measured gases (CO2 = 3.3 angstrom, CH4 = 3.76 angstrom, N-2 = 3.64 angstrom and H-2 = 2.8 angstrom), selective capture of CO2 by 1' could be ascribed to the strong electrostatic interaction of CO2 with the framework. Compound 1' also shows reversible iodine uptake (1'. 4I(2): based on the sample weight measurements and TGA data) with visible color change of the compound. Interestingly, the iodine-loaded MOF showed similar to 76 times increase in electrical conductivity compared to 1'.