pH-Dependent cobalt(II) frameworks with mixed 3,3 ', 5,5 '-tetra(1H-imidazol-1-yl)-1,1 '-biphenyl and 1,3,5-benzenetricarboxylate ligands: synthesis, structure and sorption property

An exploration of reactions of 3,3', 5,5'-tetra(1H-imidazol-1-yl)-1,1'-biphenyl (L) and 1,3,5-benzenetricarboxylic acid (H3BTC) with Co(II) salt has led to the formation of three new complexes with different framework structures, [Co-2(L)(HBTC)(2)(mu(2)-H2O)(H2O)(2)]center dot 3H(2)O(1), [Co-3(L)(2)(BTC)(2)]center dot 4H(2)O (2) and [Co-2(L)(BTC)(mu(2)-OH)(H2O)(2)]center dot 2H(2)O (3). They were obtained as pH-dependent products. The H3BTC ligand is partially deprotonated in 1, but completely in 2 and 3. Furthermore, a bridging OH-is present in 3. Complex 1 consists of infinite Co(II)-L chains bridged into a layered structure via carboxylate groups of HBTC2-. In case of 2, it has a Co(II)-L 2D network which is further linked by BTC3- resulting the formation of a final 2D structure (2D + 2D -> 2D). While in 3, it is a 3D framework with Co(II)-L layers connected by BTC3-. The results showed that the pH plays an important role in determining the structure of the frameworks. The sorption properties of the complexes were investigated.