Syntheses, structures and properties of two dinuclear mercury(II) iodide compounds containing tetradentate tripodal amine/pentadentate N-donor Schiff base: Control of molecular and crystalline architectures by varying ligand matrices

Efficient removal of Hg2+, Cd2+ and Pb2+ from aqueous solution and mixed industrial wastewater using a designed chelating ligand, 2-pyridyl-N-(2'-methylthiophenyl) methyleneimine (PMTPM)

The present study is focused on the removal of Hg²⁺, Cd²⁺ and Pb²⁺ ions from aqueous solution using a tridentate chelating agent, 2-pyridyl-N-(2'-methylthiophenyl) methyleneimine (PMTPM); and applicability of such removal from industrial wastewater using PMTPM is also investigated. The results showed that the metal ions removal efficiency using PMTPM was in the order of Hg²⁺(99.46%) > Cd²⁺(95.42%) > Pb²⁺(94.54%) under optimum reaction conditions (L:M²⁺ = 3:1, pH = 9, time = 24 h, temp. = 30 °C). Formed chelated complexes such as [Hg(PMTPM)Cl₂] (1), [Cd(PMTPM)Cl₂] (2) and [Pb(PMTPM)Cl₂] (3) were characterized by numerous spectroscopic tools and X-ray structure determination of a representative complex of Hg²⁺. In the X-ray structure of [Hg(PMTPM)Cl₂], 1, the Hg²⁺ adopted a distorted tetrahedral coordination geometry surrounding two N donors of PMTPM and two chloride ions. A similar coordination geometry surrounding the respective metal centres in 2 and 3 was established. The thermogravimetric analysis (TGA) revealed a stability order of [Cd(PMTPM)Cl₂] > [Hg(PMTPM)Cl₂] > [Pb(PMTPM)Cl₂]. Further the comparative metal leaching behaviour of these chelate complexes exhibited higher stability in alkaline solution than in acidic. Moreover, PMTPM was applied in real mixed industrial wastewater with alkaline pH, and adequate removals of toxic metals were achieved.