A Cyanuric Acid Platform Based Tripodal Bis-heteroleptic Ru(II) Complex of Click Generated Ligand for Selective Sensing of Phosphates via C–H···Anion Interaction

A new
bis-heteroleptic trinuclear Ru­(II) complex (1[PF6]6) has been synthesized from electron deficient
cyanuric acid platform based copper-catalyzed azide–alkyne
cycloaddition, i.e., CuAAC click generated ligand, 1,3,5-tris [(2-aminoethyl-1H-1,2,3-triazol-4-yl)-pyridine]-1,3,5-triazinane-2,4,6-trione
(L1). Complex 1[PF6]6 displays weak luminescence (ϕf = 0.002) at room
temperature with a short lifetime of ∼5 ns in acetonitrile.
It shows selective sensing of hydrogen pyrophosphate (HP2O73–) through 20-fold enhanced emission
intensity (ϕf = 0.039) with a 15 nm red shift in
emission maxima even in the presence of a large excess of various
competitive anions like F–, Cl–, AcO–, BzO–, NO3–, HCO3–, HSO4–, HO–, and H2PO4– in acetonitrile. Selective change in the
decay profile as well as in the lifetime of 1[PF6]6 in the presence of HP2O73– (108 ns) further supports its selectivity toward
HP2O73–. UV–vis and
photoluminescence titration profiles and corresponding Job’s
plot analyses suggest 1:3 host–guest stoichiometric binding
between 1[PF6]6 and HP2O73–. High emission enhancement of 1[PF6]6 in the presence of HP2O73– has resulted in the detection limit
of the anion being as low as 0.02 μM. However, 1[PF6]6 shows selectivity toward higher analogues
of phosphates (e.g., ATP, ADP, and AMP) over HP2O73–/H2PO4– in 10% Tris HCl buffer (10 mM)/acetonitrile medium. Downfield shifting
of the triazole C–H in a 1H NMR titration study
confirms that the binding of HP2O73–/H2PO4– is occurring via
C–H···anion interaction. The single crystal
X-ray structure of complex 1 having NO3– counteranion, 1[NO3]6 shows binding of NO3– with complex 1 via C–H···NO3– interactions.