Synthesis and structural characterization of several new coordination polymers of 2-(1H-imidazol-1-yl) acetic acid

The combination of the polydentate ligand 2-(1H-imidazol-1-yl) acetic acid (Hima) with metal ions (Pb2+, Li+, Zn2+, Cd2+, Fe2+ and Co2+) leads to seven different coordination polymers: [Pb3(imaH)2Cl6]n (1, layer), [Pb(ima)2(NO3)2]n (2, chain), [Li2H(ima)2(H2O)2Cl]n (3, chain), [Zn(imaH)(ima)Cl]n (4, chain), [Cd(imaH)Cl2]n (5, chain), and [M(ima)2]n (6, M = Fe; 7, M = Co; layer). All compounds were characterized by FT-IR, elemental analysis and TG analysis, and their structures were determined by single crystal X-ray diffraction. According to the structural analysis, compound 1 shows a [Pb3Cl6] layer; compounds 2–4 show an infinite chain, but they were connected with imaH or ima bridges, respectively; compound 5 also has an infinite chain constructed of double chloride bridges; and compounds 6 and 7 exhibit layers without chloride ions involved. In these compounds, the ligand adopts two kinds of forms (anion, ima or zwitterion, imaH) and shows diverse modes of coordination. More interestingly, chloride as the second anion participated in the structural architecture based on its different affinities with metal ions. Solid-state room temperature luminescence spectra revealed that emission bands of compound 1 were located at 455 nm, compound 4 at 425 nm, and compound 5 at 550 nm (λex = 390 nm), which is mainly assigned to the Ligand–Metal Charge Transfer (LMCT).

Graphical abstractSeveral diverse coordination polymers constructed by 2-(1H-imidazol-1-yl) acetic acid and metal ions are reported, the structural architectures affected by the second anion (chloride) are also discussed. Compounds 1, 4 and 5 exhibit visible fluorescence in the solid state at room temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide