Syntheses, Structures and Properties of Zinc(II) Coordination Polymers Constructed by V-Shaped Bis-imidazole and Aromatic Carboxylate Ligands

A V-shaped bis-imidazole ligand 1,1'-(5-methyl-1,3-phenylene)-bis(1H-imidazole) (Bim) in combination with auxiliary V-shaped ligands aromatic carboxylic acids of different symmetry and functional groups was selected to react with ZnSO4 center dot 6H(2)O under solvothermal condition, and two new coordination polymers, {[Zn(Bim)(Bra)(2)]center dot CH3OH}(n) (1) and {[Zn(Bim)(Mpa)]center dot H2O}(n) (2), were obtained (Bra(-)=5-bromonicotinate and Mpa(2-)=5-methylisophthalate). The two compounds were characterized by IR spectra, element analysis, powder X-ray diffraction, single-crystal X-ray diffraction, and thermogravimetric analysis. Compound 1 features Bim-bridged one-dimensional chain structures which stack up through interchain pi center dot center dot center dot pi, C-H center dot center dot center dot pi and Br center dot center dot center dot pi interactions to form a three-dimensional supramolecule. In 2, zinc(II) ions are bridged by Mpa(2-) ligands to form left- and right-handed helical chains which are further linked into (4,4) meso layers through Bim molecules. Finally, a 3D supramolecular framework forms through the interdigitation and double pi center dot center dot center dot pi interactions between the imidazole and phenyl of Bim molecules in adjacent layers. Solid state fluorescence measurements confirm that at room temperature both free ligand Bim and complexes 1 similar to 2 displays interesting multiple emissions, and the four coordinated Zn (II) center in 1 can notably sensitize the high-energy emission of Bim. CCDC: 1061914, 1; 1061915, 2.