Exploring the complexation behavior of NpO2+ with diglycolamide in an ionic liquid vs. aqueous solution

Abstract

Complexation of NpO2+ with tetramethyl diglycolamide (TMDGA) was investigated in an ionic liquid (IL: 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, Bumim.Tf2N) with an objective to understand its complexation behaviour and its optical properies in IL and aqueous media. We successfully prepared NpO2(Tf2N) salt and its complexation with TMDGA was studied by absorption spectroscopy. Similar to aqueous medium, TMDGA formed a perfectly centrosymmetric [NpO2L2]+ complex which was evident from the disappearance of the 980 nm absorption band of neptunyl cation. The formation constant (logβ) was arrived as 3.82±0.11 and 7.13±0.24 for [NpO2L]+ and [NpO2L2]+ complexes, respectively. The logβ values were several times higher in IL medium than the values found in aqueous medium (1.37±0.05 and 2.47±0.71). Our results indicated that though the NpO2+ cation forms stronger complex with TMDGA in IL medium vis-a-vis aqueous medium, the nature of the bonding and the structural conformations in both the media are identical.