Synthesis, band structure and multi-responsive luminescence sensing behavior of two Cd(II) coordination polymers

Abstract

Rapid and sensitive sensing of toxic aromatic compounds has become one of the most important issues. Herein, we use the multifunctional 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) to assemble with the Cd(II) ion in the presence of the N-donor bis(imidazole) ligand 1,2-bis(imidazol-1-yl-methyl)benzene (obix) and 1,4-bis(imidazole-l-yl)butane (bib) to construct coordination polymers with pleasing supramolecular architectures and potential interesting luminescent sensing properties. As a result, two Cd(II) coordination polymers, namely, {[Cd(ATBIP)(obix)2(H2O)]·3H2O}n (1) and [Cd(ATBIP)(bib)]n (2), were obtained successfully using the typical solution evaporation method. Single-crystal X-ray diffraction analyses reveal that (1) shows tubular chain structure, while (2) is a necklace-like chain. The central Cd(II) ions in (1) and (2) show slightly distorted octahedral geometry. The ATBIP2- ligand shows monodentate coordination mode in (1) and bischelating coordination mode in (2). With the aid of the hydrogen bonding and the C-Br⋯π interaction, (1) and (2) further extend into a 3D supramolecular network. The analysis of the solid-state diffuse reflectance UV–Vis spectrum reveals that the wide indirect band gaps Eg exist in (1) and (2), which are confirmed by the theoretical calculation based on the density functional theory (DFT). Interestingly, the fluorescence properties of (1) and (2) are greatly dependent on the solvents. Both compounds show multi-responsive sensitive “turn-on” sensing for toluene and “turn-off” sensing for some nitro aromatics (NACs). The sensing limits for toluene and NACs reach to ppm level.