Bis-Heteroleptic Ruthenium(II) Complex of Pendant Urea Functionalized Pyridyl Triazole and Phenathroline for Recognition, Sensing, and Extraction of Oxyanions

A new bis-heteroleptic Ru^II complex based ditopic receptor, 1[PF₆]₂, having an anion binding triazole −CH unit and appended 4-fluorophenyl urea arm has been developed. ¹H NMR and isothermal titration calorimetry (ITC) experiments showed binding of 1[PF₆]₂ toward oxyanions such as phosphates (e.g., H₂PO₄^- and HP₂O₇^3-) and carboxylates (e.g., CH₃CO₂^- and C₆H₅CO₂^-) anions selectively. ¹H NMR studies showed that highly basic phosphate anions such as HP₂O₇^3-/H₂PO₄^- are bound by both −CH and −NH units of complex 1[PF₆]₂. However, comparatively less basic CH₃CO₂^-, C₆H₅CO₂^- anions interacted with the urea −NH protons only. Thermodynamic parameters obtained from ITC experiments suggested that binding of all the interacting anions with complex 1[PF₆]₂ are highly enthalpy and entropy driven processes. Importantly, complex 1[PF₆]₂ showed extraction of H₂PO₄^-, CH₃CO₂^-, and C₆H₅CO₂^- anions from aqueous solution via liquid-liquid extraction with efficiencies of 28%, 74%, and 80%, respectively. The influential role of the urea moiety in the course of extraction is demonstrated by comparison with a model complex, 2[PF₆]₂. Additionally, complex 1[PF₆]₂ is capable of selective sensing of phosphate anions among all investigated anions.