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

Abstract

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.