Sulphide and iodide anion recognition by a selective copper hydrogel of a chloro substituted terpyridine ligand

Abstract

2,2′:6′,2″-Terpyridines (tpy) are well known for their ability to form a gel in the presence of transition metals. Due to the strong binding affinities towards transition metal ions aided by non-covalent interactions, tpy tends to form hydrogel with more than one metal ion. Interestingly, a simple chloro substituted 2,2′:6′,2″-terpyridine ligand L selectively forms a gel with only Cu(II) ion in a mild acidic medium. The hydrogel has a fibrous structure and is sensitive to S2− and I− anions, which is confirmed by both morphological analysis and rheological study. The copper complex was characterized using a variety of techniques, including HRMS, ESR, FTIR, elemental analysis, and DFT calculations. Further, DFT calculations were used to study the non-covalent interactions within the complex and to understand why the hydrogel responds to specific anions. The free energies of the CuI and CuS precipitate formation were calculated to get an idea of the feasibility of the process. Notably, UV–visible absorption spectroscopic study shows that the copper(II) complex CuCl2L selectively detected S2− and I− anions in aqueous acetonitrile with LOD of 2.63 and 2.08 μM, respectively.