A multitechnique approach with theoretical insights has been employed to understand the complexation of trivalent lanthanides with two β-diketones, viz. 1-phenyl-1,3-butanedione (L 1 ) and 4,4,4-trifluoro-1-phenyl-1,3-butanedione (L 2 ), in an ionic liquid (C6mim·NTf2). UV–vis spectral analysis of complexation using Nd3+ revealed the predominance of ML2 + and ML4 – species. The stability constants for the PB complexes were higher (β2 ∼ 10.45 ± 0.05, β4 ∼ 15.51 ± 0.05) than those for the TPB (β2 ∼ 7.56 ± 0.05, β4 ∼ 13.19 ± 0.06). The photoluminescence titration using Eu3+ corroborated the same observations with slightly higher stability constants, probably due to the higher ionic potential of Eu3+. The more asymmetric (AL2 ML4 ∼ 5.2) Eu-L2 complex was found to contain one water molecule in the primary coordination sphere of Eu3+ with more covalency of the Eu3+-O bond (Ω2 L1 = 8.5 × 10–20, Ω4 L1 = 1.3 × 10–20) compared to the less asymmetric Eu-L1 complex (AL1 ML4 ∼ 3.5) with two water molecules having less Eu–O covalency (Judd-Offelt parameters: Ω2 L1 = 7.3 × 10–20, Ω4 L1 = 1.0 × 10–20). Liquid–liquid extraction studies involving Nd3+ and Eu3+ revealed the formation of the ML4 – complex following an ‘anion exchange’ mechanism. The shift of the enol peak from 1176 to 1138 cm–1 on the complexation of the β-diketones with Eu3+ was confirmed from the FTIR spectra. 1H NMR titration of the β-diketones with La­(NTf2)3 evidenced the participation of α-H of the β-diketones and protons at C2, C4, and C5 positions of the methylimidazolium ring. For the ML2 complex, 4 donor O atoms are suggested to coordinate to the trivalent lanthanides with bond distances of 2.3297–2.411 Å for La–O, 2.206–2.236 Å for Eu–O, and 2.217–2.268 Å for Nd–O, respectively, while for the ML4 complex, 8 donor O atoms were coordinated with bond lengths of 2.506–2.559 Å for La–O, 2.367–2.447 Å for Eu–O, and 2.408–2.476 Å for Nd–O. The Nd3+ ion was higher by 9.7 kcal·mol–1 than that of the La3+ ion for the 1:4 complex. The complexation energy with L1 was quite higher than that with L2 for both 1:2 and 1:4 complexes. Using cyclic voltammetry, the redox behavior of trivalent lanthanides Eu and Gd with β-diketonate in ionic liquid medium was probed and their redox energetic and kinetic parameters were determined.