Europium (III) complexes of amino acid-derived bis-imine-substituted phenanthroline ligands for phosphate recognition

[Display omitted] Phenanthroline-based chiral hexadentate ligands L1, L2 and L3, as well as their europium (III) complexes 1–3 are synthesized and characterized. The coordination compounds show strong red emission typical for europium (III) derivatives. Various anionic species, F−, Cl−, Br−, I−, SO42−, NO3−, NO2−, HPO42−, CO32−, HCO3− and OAc−, are employed to evaluate the chemo-sensor properties of the complexes using fluorescence spectroscopy. For complex 1, only the addition of HPO42− leads to quenching of luminescence. For the other complexes 2 and 3, NO2− and HPO42− exhibit a strong response in the emission properties. However, complexes 2 and 3 are found to be more sensitive for HPO42− than for NO2−. The corresponding binding constants (logKβ) of the adducts are determined using the Benesi-Hildebrand method. The described studies show that the europium(III) complexes of the hexadentate ligands L1-3 can be considered as highly specific sensors for the recognition of phosphates with some competition by NO2− ions. While phosphate binding is strong in all three examples, the sensitivity for nitrite increases in the order 1