Selective and efficient detection of MnO₄^-, CrO₄^2- and Cr₂O₇^2- in aqueous solutions with two novel bis-oxime...

Detection of MnO₄^-, CrO₄^2- and Cr₂O₇^2- in aqueous solutions is of importance for environmental protection. Herein, a new bis-oxime-type ligand H₃L was thoughtfully designed and synthesized, H₃L = ((1E,1'E)-O,O'-((2-hydroxy-5-methyl-1,3-phenylene)bis(methylene))bis(1-(2-hydroxy-3-methoxyphenyl)-2-hydroxy-3- methoxybenzaldehyde oxime)). Two Zn(II) complexes, [Zn₆L₂ (μ₂-OAc)₄(μ₃-OH)₂] (1) and [Zn₄L₂(μ₃-OCH₃)₂·MeOH] (2), were constructed by slow evaporation at room temperature. Considering the excellent performance of the Zn(II) complexes in the field of fluorescence analysis and sensing, fluorescence sensing experiments were conducted on MnO₄^-, CrO₄^2- and Cr₂O₇^2- in aqueous solutions. The experimental results indicate that the two Zn(II) complexes exhibited high selectivity and sensitivity for the detection of MnO₄^-, CrO₄^2- and Cr₂O₇^2- by fluorescence quenching. Both sensors have a relatively low detection limit for MnO₄^-, CrO₄^2- and Cr₂O₇^2-, and have a high quenching constant (The K_sv of 1 for MnO₄^- is 7.29 × 10⁵ M^-1; for CrO₄^2- is 1.40 × 10⁶ M^-1, and for Cr₂O₇^2- is 2.23 × 10⁵ M^-1. The K_sv of 2 for MnO₄^- is 6.59 × 10⁵ M^-1; for CrO₄^2- is 9.26 × 10⁵ M^-1, and for Cr₂O₇^2- is 1.40 × 10⁵ M^-1). Through hirshfeld surface analysis, the presence of hydrogen bonding interactions and π···π interactions in 1 and 2 was calculated. Moreover, sensor-coated portable PMMA (polymethylmethacrylate) luminescent films devices were fabricated for easy and rapid on-site detection of the MnO₄^-, CrO₄^2- and Cr₂O₇^2- in aqueous solutions.