A schiff base and its copper(II) complex as a highly selective chemodosimeter for mercury(II) involving preferential hydrolysis of aldimine over an ester group

Abstract

The syntheses of a new Schiff base, diethyl-5-(2-hydroxybenzylidene)aminoisophthalate (HL), and a copper complex, [Cu(L₂)] (1), imparting L^-, have been described. Both the ligand HL and complex 1 have been thoroughly characterized by elemental analyses, electrospray ionization mass spectrometry, FT-IR, NMR (¹H and ¹³C), electronic absorption, and emission spectral studies and their structures determined by X-ray single-crystal analyses. Distinctive chemodosimetric behavior of HL and 1 toward Hg²⁺ has been established by UV/vis, emission, and mass spectral studies. Comparative studies further revealed that the chemodosimetric response solely originates from selective hydrolysis of the aldimine moiety over the ester group and 1 exhibited greater selectivity toward Hg²⁺ relative to HL while the sensitivity order is reversed. Further, these followed different hydrolytic pathways but ended up with the same product analyzed for diethyl-5-aminoisophthalate (DEA). Hg²⁺-induced displacement of Cu²⁺ and subsequent hydrolysis of the −HC═N– moiety in 1 affirmed the identity of the actual species undergoing hydrolysis as HL. The occurrence of Cu²⁺ displacement and Hg²⁺ detection via hydrolytic transformation has been supported by various physicochemical studies.