The diverse structures of Cd(ii) coordination polymers with 1,3,5-benzenetribenzoate tuned by organic bases

Abstract

The reaction of CdCl₂·1.5H₂O with 1,3,5-benzenetribenzoic acid (H₃BTB) in DMF gave {[Cd₃(BTB)₂(DMF)₄]·3DMF}_n (1), while the reactions of Cd(Ac)₂·2H₂O with H₃BTB in DMF/H₂O (1 : 10) in the presence of py, bpy, and bib generated {(Hpy)[Cd(BTB)(py)]·0.5DMF·3H₂O}_n (2), {Cd[Cd₂(BTB)₂(bpy)]·2bpy·DMF·19H₂O}_n (3), and {[Cd₃(BTB)₂(bib)₃(H₂O)₂]·4H₂O}_n (4), respectively (DMF = N,N′-dimethylformamide, py = pyridine, bpy = 4,4′-bipyridine, bib = 1,4-bis(imidazol-1-yl)butane). X-Ray single-crystal analyses reveal that 1 contains a two-dimensional bilayer structure based on a carboxylate and DMF bridged Cd₃ cluster. In 2, two honeycomb-like [Cd(BTB)]_nⁿ⁻ sheets are interpenetrated with each other to form a 2D network. In 3, the 2D [Cd(BTB)]_nⁿ⁻ honeycomb-like sheets are pillared by bpy to form a 3D framework, and the 3D frameworks are three-fold interpenetrated to generate the framework of 3 with 1D open channels, which are occupied by disordered Cd ions, bpy, DMF and water molecules. Compound 4 consists of a 3D self-penetrated framework constructed by μ₂-bib bridging five-fold interpenetrated 2D bilayers. The results of gas sorption measurements indicate that the desolvated 3 can selectively adsorb CO₂ and H₂ over N₂, with a rare large hydrogen sorption hysteresis. The luminescent properties of 1–4 were also investigated.