A Chemodosimetric Approach for Fluorimetric Detection of Hg²⁺ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

Abstract

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N 2 O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn 3 L 2 (OAc) 4 ] (1) and [Cd 3 L 2 (OAc) 4 ] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg 2+ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg 2+ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV−vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, 1 H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

In Situ Assembled Polynuclear Zinc Oxo Clusters Using Modified Schiff Bases as Ligands

“…To understand in detail the electronic transition behavior of 1, 2 , and 4 , DFT calculations 24 for 1 were performed. DFT calculations show that the transition corresponding to 352.79 nm is for the H-2 → L/H-3 → L/H-4 → L/H-1 → L/H-6 → L molecular orbital (MO) transition of an oscillator strength ( f ) of 0.0116, which is close to the experimental value of 355 nm ( Table S5 ).…”

Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors

“…In addition, the electrospun fibrous strips with grafted TPE and dithioacetal moieties are designed for the detection of trace Hg 2+ with the visual change of color strip from green to blue [107]. Abani et al [108] reported a trinuclear Zn(II)/Cd(II) Schiff base complexes 80 and 81 for the detection of Hg 2+ in aqueous medium via chemodosimetric approach (Figure 27). Two absorption maxima at 388 nm and 390 nm were red-shifted and the colorless solution turned to distinct yellow.…”

Insight into two unusual stable homomultinuclear copper (II)‐based bis (salamo)‐type complexes

“…Over the years, salen‐type N 2 O 2 ‐donor ligands, [ 1–5 ] as building units of polymetallic systems, have attracted more and more attention. [ 6–8 ] These N 2 O 2 ‐donor ligands can form a variety of complexes and exhibit unique optical [ 9–11 ] and catalysis properties [ 12,13 ] and are currently of interest because of their potential applications in the preparation of new optical or catalysis materials and perfect probes. [ 14,15 ] In addition, they have outstanding performance in supermolecular building and chiral complexes.…”