Three Co(II) Metal-Organic Frameworks with Diverse Architectures for Selective Gas Sorption and Magnetic Studies

Three Co(II) metal-organic frameworks, namely, {[Co-2(L)(2) (OBA)(2) (H2O)(4)]center dot xG}(n) (1), {[Co(L)(0.5)(OBA)]center dot xG}(n) (2), and {[Co-2(L)(2)(OBA)(2)(H2O)]center dot DMA center dot xG}(n) (3) [where L = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene, H(2)OBA = 4,4'-oxybisbenzoic acid, DMF = dimethylformamide, DMA = dimethylacetamide, and G denotes disordered guest molecules], have been synthesized under diverse reaction conditions through self-assembly of a bent dicarboxylate and a linear spacer with a Co(II) ion. While 1 is crystallized at room temperature in DMF to form a 2D layer structure, 2 is formed by the assembly of similar components under solvothermal conditions with a 3D network structure. On the other hand, changing the solvent to DMA, 3 could be crystallized at room temperature with a 3D architecture. Out of the three, activated sample 2 was found to be permanently microporous in nature, with a BET surface area of 385 m(2)/g, and exhibited moderately high uptake capacity for C2H2 and CO2 while taking up much less CH4 and N-2 at ambient conditions. As a result, high ideal adsorbed solution theory (LAST) separation selectivities are obtained for CO2/N-2 (15:85), CO2/CH4(50:50), and C2H2/CH4(50:50) gas mixtures, making 2 a potential candidate for those important gas separations at ambient conditions. Moreover, the magnetic properties of 1-3 were studied. 1 and 2 show antiferromagnetic interaction between the Co(II) centers, whereas 3 displays ferromagnetic behavior arising from a counter-complementary effect between two types of links among Co(II) centers in 3.