Synthesis, crystal structures, and luminescence properties of seven tripodal imidazole-based Zn/Cd(ii) coordination polymers induced by tricarboxylates†
Seven tripodal imidazole-based metal coordination polymers, [Zn3(L1)2(tib)2]n·(H2O)4n (1), [Cd3(L1)2(tib)2(H2O)2]n·(H2O)6n (2), [Zn3(L2)2(tib)2]n·(H2O)n (3), [Cd3(L2)2(tib)2]n·(H2O)6n (4), [Zn3(L3)2(tib)2]n·(H2O)4.5n (5), [Zn2(HL3)2(tib)2]n·(H2O)n (6), and [Cd3(L3)2(tib)2(H2O)2]n·(H2O)4n (7), with different structures have been designed and prepared based on the hydrothermal reaction between Zn(OAc)2·2H2O or Cd(OAc)2·2H2O and tib ligands in the presence of three asymmetric semi-rigid V-shaped tricarboxylate ligands, H3L1–3, where tib, H3L1, H3L2, and H3L3 ligands represent 1,3,5-tris(1-imidazolyl)benzene, 3-(2-carboxyphenoxy)phthalic acid, 4-(2-carboxyphenoxy)phthalic acid, and 3-(4-carboxyphenoxy)phthalic acid, respectively. All of these compounds, sharing three-dimensional (3D) networks, have been clearly identified by single crystal X-ray diffraction analysis. Among complexes 1–7 (except 6), the common 3D skeletons are composed of tib N-donor ligands bridging two-dimensional (2D) sheets made of L1–3 ligands and metal ions. Compound 6 also exhibits a 3D network constructed from partly deprotonated L3 ligands attached to right- and left-helices made of tib ligands and Zn ions. In these compounds, the diversity of the tib ligand-based metal building units is tuned by the molecular conformation of the tricarboxylates and the coordination geometry of the metal ion. In addition, the thermal stability and emission spectroscopy for the series of seven complexes have also been investigated.