Synthesis, Structures And Properties Of The Functional Complexes Constructed From 2-Propy-1H-Imidazole-4,5-Dicarboxylic Acid

We used an organic ligand 2-Propyl-1H-Imidazole-4,5-Dicarboxylic acid (H3L) to react with transition metal ions or main group metal ions in hydrothermal method, and obtained nine novel complexes. Their syntheses, crystal structures, fluorescent behaviors and thermogravimetric (TG) analysis were studied.Firstly, H3L was used to react with Cd(Ⅱ), Ni(Ⅱ), Co(Ⅱ) or Mn(Ⅱ) ions, and hydrothermally got four mononuclear complexes:[Cd(H2L)2(2,2'-bipy)] (1), [Ni(H2L)2(H2O)2] (2), [Co (H2L)2(H2O)2] (3) and [Mn (H2L)2(H2O)2] (4). At the same time, the reaction of Co(Ⅱ) ion with ligand H3L produces one tetranuclear complex: [Co4(L)4(2,2'-bipy)4] (5). In 1-5, central metal Cd(Ⅱ), Ni(Ⅱ), Co(Ⅱ) and Mn(Ⅱ) ions all show six coordination environment, and form a slightly distorted octahedral geometry.Secondly, we also used H3L to react with Ca(Ⅱ), Sr(Ⅱ), Ba(Ⅱ), Pb(Ⅱ) ions through hydrothermal reaction, and got four novel coordination polymers:[Ca(H2O)2(HL)]n (6), [Sr(H2L)2(H2O)2]n (7), [Ba(H2L)2(H2O)3]n (8) and [Pb3(HL)3]n (9). In compound 6, each ligandμ5-η8 bridges Ca(II) ion forming 3-D structure, this coordination mode of the coordination polyers constructed from ligand H3L is found in the first time; In compound 7, each Sr(II) shows eight coordination environment, and form a dodecahedron geometry. Each ligandμ2-η3 bridges Sr(II) ion forming 2-D sheet. In compound 8, each Ba(II) shows seven coordination environment, and form a single-cap octahedron geometry. Each ligandμ2-L bridges Ba(II) ion forming 1-D chain; In compound 9, each ligandμ4-η7 bridges Pb(Ⅱ) ion forming 3-D structure.Finally, thermostabilities of complexes 1-9 were determined by TG and DSC testing. Solid-state fluorescent properties of these complexes were also studied. The solid-state emission spectra of complexes 1-4 showed that introduction the metal ions can enhance or weaken the intraligand transitions L*→L of H3L. While in the main group metal complexes 6-9, Fluorescence emission peaks of 6 and 8 can be explained by charge transfer transition luminescence between the ligand and the central metal ion, fluorescence emission peak of 7 is attributed to charge transfer transition luminescence within the ligand, fluorescence emission peak of 9 is attributed toπ-π* transition and n-π* transition after ligand coordination. In the UV spectrum, the absorption peaks of the complexes 1-9 can be attributed toπ-π* absorption band of the ligand.