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, [Co2(L)(HBTC)2(μ2-H2O)(H2O)2]·3H2O (1), [Co3(L)2(BTC)2]·4H2O (2) and [Co2(L)(BTC)(μ2-OH)(H2O)2]·2H2O (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.