Colorimetric Detection of Pollutant Trivalent Cations and HSO4− in Aqueous Media Using a New Schiff-base Probe: An Experimental and DFT Studies

Synthesis, crystal structure, Hirshfeld surface analysis, energy frameworks and computational studies of Schiff base derivative

The compound (E)-ethyl 3-(2-(2,4-dinitrophenyl)hydrazono)butanoate (3) was synthesised and crystallized using ethanol as a solvent. The compound was characterized by ¹H NMR, and single crystal X-ray diffraction. The compound crystallizes in the monoclinic crystal system with the space group P2₁/c. The intermolecular interactions and the interaction energies responsible for the stabilization of the molecules were determined by Hirshfeld surface analysis and energy framework calculations. The structure of the compound was optimized by Density Functional Theory calculations and HOMO–LUMO energy gap was calculated. The non–covalent interactions were revealed by reduced density gradient analysis. The Mulliken atomic charges and natural atomic charges were calculated by density functional theory calculations. The reactive sites present in the molecule are shown by molecular electrostatic potential map. The inter and intra molecular charge transfer were investigated by NBO analysis.

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Crystal structure was confirmed by X-ray diffraction analysis and the atomic coordinates were optimized by DFT calculations.

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Hirshfeld surface analysis and energy frameworks calculations were carried out.

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HOMO - LUMO frontier molecular orbitals and molecular electrostatic potential were studied.

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Reduced density gradient (RDG), and topology analyses were performed.

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Natural bond orbital analysis was performed to study intramolecular charge transfer.

Tailoring an HSO4- anion hybrid receptor based on a phenazine derivative

A catechol-functionalized phenazine imidazole (PD) was tailored with 2,3-diaminophenazine and 3,4-dihydroxy benzaldehyde, and it served as a hybrid acceptor for capturing HSO₄^- anions. The selectivity and sensitivity of the PD receptor for anion sensing were studied. It was found that the PD receptor could not only display a preferable sensitivity to HSO₄^- ions with a "turn-off" fluorescence response, but also have a strong anti-interference ability toward other common anions, especially basic anions such as CH₃COO^-, HPO₄^2-, and H₂PO₄^-. The anion recognition mechanism of PD towards HSO₄^- is based on multiple hydrogen bond interactions. Finally, the strips for anion detection were prepared, which were verified to be a convenient and high-efficiency test kit for detecting HSO₄^- ions with the naked eye.