Detection of copper(ii) and aluminium(iii) by a new bis-benzimidazole Schiff base in aqueous media via distinct routes

Abstract

The synthesis is described of a new bis-benzimidazole appended Schiff base ligand [2-(3,5-bis(1H-benz-imidazol-2-yl)-phenyliminomethyl)phenol] (H₃L) followed by its thorough characterization by elemental analyses, spectroscopic studies (FT-IR, ¹H, ¹³C NMR, ESI-MS, UV/vis, fluorescence) and X-ray single crystal analyses. The excellent selectivity of H₃L towards Cu²⁺ and Al³⁺ via distinct responses in mixed aqueous conditions was established by spectroscopic studies. The selective detection of Cu²⁺ due to the creation of complex 1 in which Cu²⁺ occupied only the salen-type N₂O₂ coordination site and the strong binding with Al³⁺ through both benzimidazole and salen moieties to yield complex 2 was confirmed by various studies. The disparate detection of these cations by H₃L was substantiated by comparative studies, performed under analogous conditions, of the precursor compound 3,5-bis(1H-benzimidazol-2-yl)-aniline (BBA). The distinct interaction of H₃L with Cu²⁺ and Al³⁺ and the sensing mechanisms were investigated in detail by spectroscopic studies and were supported by theoretical studies (Density Functional Theory). It has been clearly shown that the use of appropriate substituents may facilitate the design and development of probes suitable for the real time detection of more than one analyte.