Alkali-metal-regulated construction of superhydrophilic ZnII and CdII coordination polymers with perhalogenated terephthalate ligands

Abstract

By simply introducing different alkali metal ions as structure-directing agents, four new coordination polymers with the formulae [Cd₃(BDC-F₄)₃(DMF)₂(MeOH)₆]_n (1), [Cd(BDC-F₄)(DMF)₂(H₂O)₂]_n (2), [Zn₂Na₂(BDC-Cl₄)₃(DMF)₄(μ₂-MeOH)]_n (3) and [ZnK(BDC-Cl₄)_1.5(DMF)(Me₂NH)]_n (4) (BDC-F₄ = 2,3,5,6-tetrafluoro-benzenedicarboxylate; BDC-Cl₄ = 2,3,5,6-tetrachloro-benzenedicarboxylate; DMF = dimethylformamide and Me₂NH = dimethylamine) have been synthesized and structurally characterized. Complex 1 presents an open three-dimensional (3D) 3-nodal (3,4)-connected framework, 2 has a one-dimensional (1D) chain structure, 3 features a 3D 4-nodal (3,4,5,6)-connected coordination network constructed from the new Zn^II–Na^I heterometallic tetranuclear cluster, and 4 shows a 3D 4-nodal (3,5,6)-connected network based on the unique Zn^II–K^I heterometallic tetranuclear cluster. The results reveal the significant influence of alkali-metal ions on the structural topologies of complexes 1–4. Interestingly, compounds 1–4 all exhibit high water solubility, and futher evaporation of their water solution will result in a 1D coordination polymer {[Cd₄(BDC-F₄)₄(H₂O)₁₁]·3.5H₂O}_n (5) consisting of the unprecedented polymeric [Cd^II–H₂O]_n chain, and a zero-dimensional (0D) complex [Zn(H₂O)₆]·(BDC-Cl₄)·4H₂O (6) containing the discrete [Zn(H₂O)₆]²⁺ cationic and BDC-Cl₄ dianionic moieties. Furthermore, the solution chemistry of complexes 5 and 6 has been investigated by electrospray ionization (ESI) mass spectrometry and molar electrical conductivity. The photoluminescent properties of complexes 1–6 have also been explored, which interestingly indicate a strong blue emission of complex 1 in the solid state at room temperature.