Two cobalt(II) metal-organic frameworks based on mixed 1,2,4,5-benzenetetracarboxylic acid and bis(benzimidazole) ligands

Two cobalt(II) metal-organic frameworks constructed from 1,2,4,5-benzenetetracarboxylic acid and flexible bis(5,6-dimethylbenzimidazole) ligands, namely {[Co-1.5(Hbtec)(L1)(1.5)(H2O)(2)]center dot(H2O)} (n) and {[Co(H(2)btec)(L2)]center dot(L2)(0.5)(H2O)(2)} (n) [L1 = 1,4-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, L2 = 1,4-bis(5,6-dimethylbenzimidazole)butane], have been hydrothermally synthesized and characterized by physicochemical and spectroscopic methods and by single-crystal X-ray diffraction. The cobalt atoms present different coordination environments, with trigonal-bipyramidal and octahedral geometries in 1, and a tetrahedral geometry in 2. Complex 1 has a 2D (6,3) wave like layer structure, which is further linked by hydrogen bonding to generate a 3D supramolecular architecture. It is a trinodal (4,4,4)-connected topology with a point symbol of {4(2)center dot 6 center dot 8(3)}(2){4(2)center dot 6(2)center dot 8(2)}{4(3)center dot 6(3)}(2). Complex 2 is a 2D (6,3) honeycomb net, further linked into a 3D supramolecular network via two modes of pi-pi stacking interactions. The degradation of methyl orange in a Fenton-like process using complexes 1 and 2 as catalysts has been investigated.