A homobimetallic nickel(II) complex for discriminative chromogenic recognition of aqueous cyanide and silver(I) from medicinal products: Role of end-on thiocyanate bridging

Abstract

Herein, a homobimetallic azomethine-functionalized nickel(II) complex, [Ni₂L₂(van)(μ_1,1-NCS)] (AMR-1, where L = 2-[(2-Hydroxy-1,1-dimethyl-ethylimino)-methyl]-6-methoxyphenol, molecular weight = 788.20 (found)) has been judiciously synthesized with N-coordinated end-on thiocyanate. AMR-1 exhibited promising chromogenic variation from pale green to colourless with hypochromic shifting in the visible region in the presence of silver(I). Herein, the exposed sulfur site of the co-ligand acts as chemodosimetric recognition site for highly selective detection of a soft metal pollutant, silver ion (Ag⁺) with the limit of detection (LOD) of 0.37 ppm. Along with this, aqueous cyanide (CN⁻) recognition was accomplished in a mutually independent way with distinct chromogenic variation from pale green to yellowish color within ∼5 s. This led to the LOD of 0.46 ppm, which is much lower than the safe limit, set by the World Health Organization (WHO). The stability constant value for cyanide interaction with AMR-1 is obtained to be 1.49 × 10³ M⁻¹ as per 1:1 binding stoichiometry. Experimental findings, obtained from UV–Vis, HR-MS, FT-IR, and ¹H NMR spectroscopic studies in conjugation with the decreased HOMO-LUMO energy gap from 3.40 eV to 2.07 eV, obtained from density functional theory studies, support the mechanistic pathway of interaction. Implementing molecular logic platforms benefits from fabricating three-input-two-output logic circuits by imitating variable spectroscopic outcomes. Real-time multifarious applications of AMR-1 have been accomplished with paper strip-based solid-state assay and recognition of the target-specific analytes from targeted medicinal specimens and from both cyanogenic as well as non-cyanogenic food sources. To the best of our knowledge, this is probably the first nickel(II) complex derived sensory receptor that is effectually implemented towards recognition of another metal ion, silver (I) along with CN⁻ from aqueous as well as from real specimens.