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

Abstract

A new bis-heteroleptic Ru II complex based ditopic receptor, 1 [PF 6 ] 2, having an anion binding triazole −CH unit and appended 4-fluorophenyl urea arm has been developed. 1 H NMR and isothermal titration calorimetry (ITC) experiments showed binding of 1 [PF 6 ] 2 toward oxyanions such as phosphates (e.g., H 2 PO 4 – and HP 2 O 7 3– ) and carboxylates (e.g., CH 3 CO 2 – and C 6 H 5 CO 2 – ) anions selectively. 1 H NMR studies showed that highly basic phosphate anions such as HP 2 O 7 3– /H 2 PO 4 – are bound by both −CH and −NH units of complex 1 [PF 6 ] 2 . However, comparatively less basic CH 3 CO 2 –, C 6 H 5 CO 2 – 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 [PF 6 ] 2 are highly enthalpy and entropy driven processes. Importantly, complex 1 [PF 6 ] 2 showed extraction of H 2 PO 4 –, CH 3 CO 2 –, and C 6 H 5 CO 2 – 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 [PF 6 ] 2 . Additionally, complex 1 [PF 6 ] 2 is capable of selective sensing of phosphate anions among all investigated anions.