Ionic Liquid Assisted Exothermic Complexation of Trivalent Lanthanides with Fluorinated β Diketone: Multitechnique Approach with Theoretical Insight
Adityamani Nagar, Arijit Sengupta, Sk. Musharaf Ali, Prasanta K. Mohapatra
Abstract
The complexation of the betadiketone,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (HFOD) was studied with trivalent lanthanide ions, viz. Nd 3+, La 3+, and Eu 3+ in several methylimidazolium-based ionic liquids (C n mim•NTf 2, where, n = 4,6,8). In C 6 mim•NTf 2, predominant formation of ML 2 + and ML 4 – species was evidenced from the UV–vis absorption (Nd 3+ ) as well as luminescence (Eu 3+ ) spectral studies with log β 2 ≈ 5.88 ± 0.04, log β 4 ≈ 10.95 ± 0.06. The formation constants followed the trend C 4 mim•NTf 2 > C 6 mim•NTf 2 > C 8 mim•NTf 2 . The asymmetry factors for the ML 2 + and ML 4 – species were found to be 1.2 and 1.59, respectively. The ML 4 – complex was found to have one primary coordination sphere water molecule with enhanced covalency between Eu 3+ and O from HFOD (Judd Offelt constants Ω 2 and Ω 4 ≈ 17.2 and 2.35) compared to Eu 3+ aq, yet comparable to other β diketones. Complexation-induced temperature increase was confirmed by calorimetric measurements, indicating the exothermic complexation reaction (Δ H complexation ≈ −13.7 kJ mol –1 ), which is also spontaneous in nature (Δ G ≈ −68.1 kJ mol –1 ), with an enhancement in the entropy values. Due to complexation, the shifts in the peak positions (1686.66 cm –1, 1633.53 cm –1 ) associated with β diketone/ketone functional groups were evidenced. Density functional theory (DFT) calculation was performed to optimize the structural parameters including bond distance, bond angles, and energetics associated with the complexation.