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

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.