Complexation Behavior of Uranyl Ion With Amide Functionalized Ionic Liquids: Synthesis, Complexation, and Spectroscopic Study

ABSTRACT

Task‐specific ionic liquids (TSILs) featuring an amide functional group grafted covalently to an alkyl‐substituted triazolium cation was successfully synthesized and characterized, using ¹ H NMR spectroscopy, FTIR spectroscopy, and ESI‐MS analysis. The coordination behavior and complexation thermodynamics of UO ₂ ²⁺ ions of the synthesized TSILs namely (1‐benzyl‐4‐N‐(benzylacetamido)‐1,2,4‐triazol‐4‐ium) bis(trifluoromethanesulfonyl) imide) [TSIL‐1] and (1‐butyl‐4‐((benzylacetamido)‐1,2,4‐triazol‐4‐ium) bis(trifluoromethane sulfonyl)imide) [TSIL‐2] was systematically investigated in two methylimidazolium‐based ionic liquids (C ₄ mim•NTf ₂ and C ₈ mim•NTf ₂ ) using UV–Vis spectroscopy and Photoluminescence measurements. On increasing the aliphatic nature of the substituent from benzyl to butyl enhances the complexation strength with uranyl cations due to reduced steric hinderance and improved electron donation. Among the two TSIL, it was found that TSIL‐2 demonstrated more predominant ML ₄ complexes with logβ =  11.55 ± 0.07 and— ΔG (kJ) =  66.38 ± 0.40 in C ₄ mim•NTf ₂ ionic liquid medium and logβ =  11.27 ± 0.13 and ΔG (kJ) =  −64.77 ± 0.75 in C ₈ mim•NTf ₂ ionic liquid medium, whereas the TSIL‐1 exhibited predominant formation of the ML ₃ type complexes having logβ =  7.67 ± 0.07 and— ΔG (kJ) =  −44.08 ± 0.40 & logβ =  7.26 ± 0.15 and ΔG (kJ) =  −41.72 ± 0.86 in C ₄ mim•NTf ₂ and C ₈ mim•NTf ₂ respectively. The effect of temperature on stability constants was also examined by performing titration also at 40 °C and 50 °C to access the influence of the thermal variation on the stability of complexes. In both the TSILs, the plot of logβ v/s 1/T showed linearity indicating an enthalpically driven interaction.