Calix[4]arene-based 1,3-diconjugate of salicylyl imine having dibenzyl amine moiety (L): synthesis, characterization, receptor properties toward Fe²⁺, Cu²⁺, and Zn²⁺, crystal structures of its Zn²⁺ and Cu²⁺ complexes, and selective phosphate sensing by the [ZnL]

Abstract

A calix[4]arene conjugate bearing salicylyl imine having dibenzyl moiety (L) has been synthesized and characterized, and its ability to recognize three most important essential elements of human system, viz., iron, copper, and zinc, has been addressed by colorimetry and fluorescence techniques. L acts as a sensor for Cu²⁺ and Fe²⁺ by exhibiting visual color change and for Zn²⁺ based on fluorescence spectroscopy. L shows a minimum detection limit of 3.96 ± 0.42 and 4.51 ± 0.53 ppm and 45± 4 ppb, respectively, toward Fe²⁺, Cu²⁺, and Zn²⁺. The in situ prepared [ZnL] exhibits phosphate sensing among 14 anions studied with a detection limit of 247 ± 25 ppb. The complexes of Zn²⁺, Cu²⁺, and Fe²⁺ of L have been synthesized and characterized by different techniques. The crystalline nature of the zinc and copper complexes and the noncrystalline nature of simple L and its iron complex have been demonstrated by powder XRD. The structures of Cu²⁺ and Zn²⁺ complexes have been established by single crystal XRD wherein these were found to be 1:1 monomeric and 2:2 dimeric, respectively, using N₂O₂ as binding core. The geometries exhibited by the Zn²⁺ and the Cu²⁺ complexes were found to be distorted tetrahedral and distorted square planar, respectively. The iron complex of L exists in 1:1 stoichiometry as evident from the mass spectrometry and elemental analysis.