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

A new bis-heteroleptic RuII 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 HP2O73-) and carboxylates (e.g., CH3CO2- and C6H5CO2-) anions selectively. 1H NMR studies showed that highly basic phosphate anions such as HP2O73-/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.