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.