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 (1(a) of 5.28 X 10(4) M-1 and 4.67 X 10(4) M-1 for H2PO4- and HP2O73-, respectively, which is in good agreement with the K-a values obtained from UV-vis titration experiments (2.97 X 10(4) M-1 and 2.45 X 10(4) 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 (tau) as well as in the decay pattern of 1[PFe6](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- (Delta delta = 0.26 ppm) and HP2O73- (Delta delta = 0.23 ppm) in deuterated dimethyl sulfoxide proclaim binding mechanism via C-H center dot center dot center dot 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 center dot center dot center dot anion interactions.