A series of Zn(II) coordination polymers derived from dicarboxylate acids and flexible imidazole-based ligands: Syntheses, crystal structures and photoluminescent properties

Abstract

Five coordination polymers based on 1,4-bis(2-methylimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (bmimx), namely, {[Zn(bmimx)(1,2-BDC)]·3H2O}n (1), [Zn(bmimx)0.5(1,2-BDC)]n (2), [Zn(bmimx)(1,3-BDC)]n (3), {[Zn(bmimx)(1,3-ADC)]·2H2O}n (4) and [Zn(bmimx)0.5(1,3-ADA)]n (5) (1,2-H2BDC=1,2-benzenedicarboxylic acid, 1,3-H2BDC=1,3-benzenedicarboxylic acid, 1,3-H2ADC=1,3-adamantanedicarboxylic acid, 1,3-H2ADA=1,3-adamantanediacetic acid) have been synthesized under hydro(solvo)thermal conditions. Though complexes 1 and 2 have the same starting materials, under the effect of binding modes of the 1,2-H2BDC ligand, complexes 1 and 2 exhibit different 2D structures. Complex 1 shows a sheet structure with hcb topology; complex 2 presents a binodal (3,4)-connected layer with 3,4L83 topology. Employments of the 1,3-H2BDC and 1,3-H2ADC ligands generate two different double chains 3 and 4, respectively. Complex 5 manifests a 2D network containing alternating left- and right-handed helical motifs in the presence of flexible dicarboxylate ligand 1,3-H2ADA, which has the same topological type as 2. The structural differences demonstrate that the backbones of the dicarboxylate acids are a key point to form the final coordination polymers. Moreover, the fluorescent properties of complexes 1–5 were studied in the solid state at room temperature.