Luminescent sulfonate coordination polymers: synthesis, structural analysis and selective sensing of nitroaromatic compounds

Abstract

With a flexible anthracene-based redox active ligand (9,10-bis((1H-imidazol-1-yl)methyl)anthracene (BIA)), a sulfonic acid coligand (1,5-naphthalenedisulfonic acids (NDS) and 5-sulfoisophthalic acid sodium salt (SIA)), six Zn(II) and Cd(II) coordination polymers (CPs), viz. [Zn(BIA)₃(NDS)₂] (CP-1a), [Zn(BIA)(SIA)] (CP-1b), [Cd(cis-BIA)₂(NDS)₂(DMF)₂] (CP-1c), [Cd(trans-BIA)₂(SIA)₂(DMF)₂] (CP-1d), [Cd₂(BIA)₂(NDS)₂(DMF)] (CP-1e) and [Cd·Na(BIA)₂(SIA)₂(DMF)₂(H₂O)] (CP-1f), were synthesized hydrothermally. These coordination polymers were characterized by IR spectroscopy, thermogravimetric analysis (TGA) and single crystal X-ray crystallography. All these CPs, with strong photoluminescence in suspensions, have been used for sensing of nitroaromatic compounds. The luminescence properties of these CPs are selectively enhanced by picric acid (PA), dinitrotoluene (DNT) and nitroaniline (NA). The effect of picric acid on the surface of the CPs was also analyzed by scanning electron microscopy. The electronic properties of the BIA ligand and CP-1b were analyzed by cyclic voltammetry. Theoretical studies were performed by DFT calculation to understand the sensing mechanism of these polymers towards PA. Gas adsorption analysis of the Cd-CPs showed negligible uptake of N₂, CO₂ and CH₄ whereas the Zn-CPs showed moderate uptake of these gases.