From 1D to 2D coordination polymers based on benzimidazole and dicarboxylate: Syntheses, structures, and fluorescence properties

Abstract

Three new Zn(II)/Cd(II) coordination polymers (CPs), {[Zn(4pybbp)(fumarate)_0.5(NO₃)]·(DMA)₂·(H₂O)_2.25}_n (1), {[Zn(4pybbp)(glutarate)]·H₂O}_n (2), [Cd(4pybbp)(isophthalate)]_n (3) (4pybbp = 2-(6-(1H-Benzo[d]imidazole-2-yl)pyridine-2-yl)-1-(pyridine-4-methylpyridine-1H-benzo[d]imidazole; DMA = dimethylacetamide) have been prepared using solvothermal method by introducing different dicarboxylate anion. Single crystal analysis shows that CP 1 and 2 are one-dimensional (1D) trapezoidal double-stranded and linear single-stranded structures, respectively, while CP 3 is two-dimensional (2D) planar structure. The structural disparities among the three coordination polymers can be ascribed to the size of d¹⁰ metal ions and the coordination mode of ligands. The solid-state fluorescence properties indicate that the fluorescence peaks of the coordination polymers 1–3 belong to the π*-π transition of the ligand 4pybbp, which occur significant blue-shift and enhancement. The order of fluorescence blue-shift is 1 > 2 > 3, which is consistent with the bond length order of Zn/Cd-N_pyridine. The stronger fluorescence of the CPs than the ligand is due to the immobilization of the ligand through coordination, which reduces the energy loss of thermal vibration. Moreover, the fluorescence intensity of coordination polymers increases with the skeleton structure from 1D to 2D. Therefore, coordination and skeleton structure will affect the fluorescence of the coordination polymers.