Four New Metal–Organic Supramolecular Networks Based on Aromatic Acid and Flexible Bis(imidazole) Ligand: Synthesis, Structures and Luminescent Properties

Abstract

Four new metal–organic supramolecular networks, namely, [Zn(H2pdc)2(H2O)2]·2H2O·bbi (1), {[Cd(Hpdc)2]·2H2O2·H2bbi}n (2), [Zn(BA)2(bbi)]n (3), and {[Cd(BA)2(bbi)]·H2O}n (4) (H3pdc = 3,5-pyrazoledicarboxylic acid, HBA = 3-hydroxybenzoic acid and bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) have been synthesized under hydrothermal conditions and characterized by IR spectra, elemental analyses, and single-crystal X-ray diffraction analyses. Compound 1 possesses zero-dimensional (0D) structure, which is finally extended into a two-dimensional (2D) supramolecular network via O–H···O and C–H···O hydrogen bonds. Complex 2 displays a 2D network structure built from Cd2+ atoms interconnected by Hpdc2− ligands. The adjacent networks are further assembled into three-dimensional (3D) supramolecular structure through O–H···O hydrogen bonds. Compounds 3 and 4 show similar one-dimensional (1D) chains, in which four-coordinated Zn(II) atoms and six-coordinated Cd(II) atoms are bridged by bbi ligands. Through O–H···O and C-H···O hydrogen bonding interactions, the 1D chains are further packed into 2D and 3D supramolecular frameworks for 3 and 4, respectively. Obviously, the structural differences among compelxes 1–4 are attributed to the different central metal atoms and organic ligands. In addition, compounds 1–4 exhibit blue fluorescent emission in the solid state at room temperature.