Bis-Heteroleptic Ruthenium(II) Complex of a Triazole Ligand as a Selective Probe for Phosphates

A new bis-heteroleptic ruthenium­(II) complex (1) of 2-(1-methyl-1H-1,2,3-triazol-4-yl) pyridine (L) ligand was extensively explored for anion sensing studies. 1[PF6]2 shows selective sensing of dihydrogen phosphate (H2PO4–)/hydrogen pyrophosphate (HP2O73–) among halides, HCO3–, AcO–, NO3–, ClO4–, HSO4–, OH–, BzO–, H2PO4–, and HP2O73– in acetonitrile. Enhancement of emission intensity of 1[PF6]2 along with a 10 nm red shift of the emission maximum is observed in the presence of H2PO4–/HP2O73– selectively. The photoluminescence (PL) titration experiment of 1[PF6]2 results in binding constants (Ka) of 5.28 × 104 M–1 and 4.67 × 104 M–1 for H2PO4– and HP2O73–, respectively, which is in good agreement with the Ka values obtained from UV–vis titration experiments (2.97 × 104 M–1 and 2.45 × 104 M–1 for H2PO4– and HP2O73–, respectively). High selectivity of 1[PF6]2 toward these two anions in acetonitrile is further confirmed by PL intensity measurement of 1[PF6]2 upon addition of these two anions in the presence of a large excess of other competitive anions. Further, considerable changes in the lifetime (τ) as well as in the decay pattern of 1[PF6]2 in the presence of H2PO4–/HP2O73– among all tested anions support the selective binding property of 1[PF6]2 toward these two anions. Significant downfield shift of the triazole −CH proton of 1[PF6]2 with 1 equiv of H2PO4– (Δδ = 0.26 ppm) and HP2O73– (Δδ = 0.23 ppm) in deuterated dimethyl sulfoxide proclaim binding mechanism via C–H···anion interaction in solution state. Finally, single-crystal X-ray structural analysis confirms the first example of dihydrogen pyrophosphate (H2P2O72–) recognition via solitary C–H···anion interactions.