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 complex based ditopic receptor, 1[PF], having an anion binding triazole -CH unit and appended 4-fluorophenyl urea arm has been developed. H NMR and isothermal titration calorimetry (ITC) experiments showed binding of 1[PF] toward oxyanions such as phosphates (e.g., HPO and HPO) and carboxylates (e.g., CHCO and CHCO) anions selectively. H NMR studies showed that highly basic phosphate anions such as HPO/HPO are bound by both -CH and -NH units of complex 1[PF]. However, comparatively less basic CHCO, CHCO 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] are highly enthalpy and entropy driven processes. Importantly, complex 1[PF] showed extraction of HPO, CHCO, and CHCO 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]. Additionally, complex 1[PF] is capable of selective sensing of phosphate anions among all investigated anions.

Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes toward Selective Sensing of Dihydrogen Phosphate

“…Phosphates play vital roles in numerous essential biological as well as environmental processes. − Thus, the development of superior selective synthetic probes for phosphates are in demand in anion recognition chemistry. ,,− During the past few years, several different heterocyclic ring systems containing neutral/cationic N–H/C–H (e.g., urea, − triazole, ,,− imidazole, − amide, − pyrrole, − etc.) moieties containing receptors have been reported for the selective recognition and sensing of phosphates.…”

“…moieties containing receptors have been reported for the selective recognition and sensing of phosphates. We have been systematically exploring the ruthenium complexes of pyridine triazole/iodotriazole and phenanthroline toward the development of a new class of metal complex based selective probes and extractants for phosphates. ,,− In this regard, initially we developed a bis-heteroleptic Ru­(II) probe containing methyl-substituted pyridyl triazole for selective sensing of H 2 PO 4 – over HP 2 O 7 3– and other common inorganic anions through a solitary C–H···anion interaction . Then we introduced a bis-heteroleptic trinuclear Ru­(II) probe on a cyanuric acid platform for sensing of higher homologue phosphates (pyrophosphate, ADP, and ATP) over dihydrogen phosphate .…”

“…Subsequently, we established a superior halogen-bonding-based bis-heteroleptic Ru­(II) complex with an iodotriazole-based phosphate sensor that showed metal-assisted second-sphere phosphate binding through solitary XB interactions . Furthermore, our group has explored Ru­(II)-polypyridyl-based receptors decorated with various pendant urea moieties for the binding and extraction of phosphates/carboxylates. ,, In all of the above probes, a wide range of other basic anions do not show any photophysical aspect of sensing behavior. Thus, in this class of probes, the basicity of anions might not govern the anion-sensing selectivity.…”

Amide-Functionalized Chalcogen-Bridged Flexible Tetranuclear Rhenacycles: Synthesis, Characterization, Solvent Effect on the Structure, and Guest Binding

“…Moreover, the presence of an amide functional group would facilitate the self-assembly process to achieve molecular systems of higher dimensionality via hydrogen-bonding interaction and selective sensing of anions and neutral molecules by providing hydrogen-bonding pockets to the host. 5 Amides serve as binding sites, although they are self-organized to act cooperatively within some convergent molecular architectures. 5d Thus, the incorporation of organic linkers containing amide functional groups in the formation of the metallacyclic structure is essential and fascinating.…”

“…Metal-containing cyclic amides resemble to the cyclic peptide structures. Moreover, the presence of an amide functional group would facilitate the self-assembly process to achieve molecular systems of higher dimensionality via hydrogen-bonding interaction and selective sensing of anions and neutral molecules by providing hydrogen-bonding pockets to the host . Amides serve as binding sites, although they are self-organized to act cooperatively within some convergent molecular architectures .…”