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 {[Cu2(HL)(H2O)2]·2DMF·2H2O}n (1), {[Co2(L)(DMA)]·H2N(Me)2}n (2), {[Co2(L)(H2O)]·H2N(Me)2}n (3), {[Mn2(L)(DMF)(H2O)]·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 [Cu2(COO)4] paddlewheel SBU, wherein six SBUs are connected by twelve HL4− to get an unprecedented Cu12 hendecahedron nanocage. 2–4 possess similar dinuclear [M2(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-P21/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. [ABSTRACT FROM AUTHOR]