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

Four new metal–organic supramolecular networks, namely, [Zn(H 2 pdc) 2 (H 2 O) 2 ]·2H 2 O·bbi ( 1 ), {[Cd(Hpdc) 2 ]·2H 2 O 2 ·H 2 bbi} n ( 2 ), [Zn(BA) 2 (bbi)] n ( 3 ), and {[Cd(BA) 2 (bbi)]·H 2 O} n ( 4 ) (H 3 pdc = 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 Cd 2+ atoms interconnected by Hpdc 2− 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.