Four new 3D metal-organic frameworks constructed by the asymmetrical pentacarboxylate: gas sorption behaviour and magnetic properties

By using an asymmetrical rigid pentacarboxylic acid ligand, 2,4-di(3',5'-dicarboxylphenyl)benzoic acid (H5L), four new three-dimensional (3D) metal-organic frameworks (MOFs), namely {[Cu-2(HL)(H2O)(2)]center dot 2DMF center dot 2H(2)O}(n) (1), {[Co-2(L)(DMA)]center dot H2N(Me)(2)}(n) (2), {[Co-2(L)(H2O)]center dot H2N(Me)(2)}n (3), {[Mn-2(L)(DMF)(H2O)]center dot H2N(Me)(2)}n (4), were solvothermally synthesized. H5L in 1-4 shows different coordination modes and can easily form various metal clusters (secondary building units, SBUs) in the final structures. 1 is a 3D porous framework with a (4,4)-connected pts topology based on the [Cu-2(COO)(4)] paddlewheel SBU, wherein six SBUs are connected by twelve HL4- to get an unprecedented Cu-12 hendecahedron nanocage. 2-4 possess similar dinuclear [M-2(COO)(5)] SBUs (M = Co, Mn), which are further extended by L5- to give rise to 3D frameworks with the uncommon (5,5)-connected nia-5,5-P2(1)/c and bnn topologies. In addition, the desolvated framework of 1 contains polar channels decorated with uncoordinated carboxylate groups, leading to selective adsorption for CO2 over CH4 at 195, 273 and 298 K. Moreover, the magnetic properties of 1-4 show that there exist antiferromagnetic interactions between metal ions.