Exchange coupled Co(ii) based layered and porous metal-organic frameworks: structural diversity, gas adsorption, and magnetic properties

Four new Co(ii) based metal-organic frameworks (MOFs) ({[Co-3(L)(TDCA)(3)(DMF)(2)](n)2nCH(3)CN}) (1), ({[Co-3(L)(2)(BDCA)(3)](n)2nCH(3)CN}) (2), {[Co-2(L)(2)(CA)(2)](n)4nCH(3)CN} (3) and {[Co-2(L)(OBBA)(2)](n)3nCH(3)CN} (4) are synthesized, where L is [4 '-(4-methoxyphenyl)-4,2 ':6 ',4 ''-terpyridine], a V-shaped flexible neutral spacer, and the four dicarboxylates are TDCA = thiophene 2,5-dicarboxylic acid, BDCA = benzene 1,4-dicarboxylic acid, CA = (1R,3S)-(+)-camphoric acid and OBBA = 4,4 '-oxybisbenzoic acid. Structural analysis reveals that 1 and 2 are two dimensional (2D) layered structures having interesting sql and hxl topologies respectively with trinuclear SBUs (secondary building units). Compound 3 has a 3D structure, whereas 4 has a 2-fold interpenetrated 3D packing structure with a paddlewheel dinuclear SBU and both have pcu topology. Magnetic investigation revealed that 1, 3 and 4 show dominant antiferromagnetic behavior, while 2 shows ferromagnetic interaction at very low temperature. Interestingly 4 shows a sharp decrease in the chi T-M value from room temperature and this may be because of the direct Co(ii)Co(ii) interaction. Gas sorption studies reveal that 1, 2 and 3 show surface areas of 11.8 m(2) g(-1), 8.3 m(2) g(-1) and 28.5 m(2) g(-1) respectively and better adsorption behavior for CO2 over CH4, whereas 4 is nonporous in nature due to its 2-fold interpenetrated structure.