Effect of Solvation? Complexation of Neodymium(III) with Nitrate in an Ionic Liquid (BumimTf2N) in Comparison with Water

Abstract

Complexation of neodymium(III) with nitrate has been investigated in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (i.e., BumimTf2N), at variable temperatures (20, 50, and 70oC) by optical absorption spectroscopy. Luminescence of Eu(III) in the same ionic liquid was studied to help evaluate the complexation of nitrate with Nd(III), and lanthanides(III) in general, in BumimTf2N. In contrast to the weak complexation between Nd(III) and nitrate in water where only Nd(NO3)2+ and Nd(NO3)2 + with very low stability constants have been found, up to six successive nitrate complexes of Nd(III), Nd(NO3)j (3-j)+ where j = 1 – 6, have been observed in dry BumimTf2N. The Nd(III) nitrate complexes in dry BumimTf2N are fairly strong, with the stability constant of Nd(NO3)2+ being seven orders of magnitude higher than that in water. Data obtained by optical absorption, diffuse reflectance, and EXFAS spectroscopy helped to illustrate the coordination mode of nitrate in the Nd(III)/nitrate complexes in dry BumimTf2N. The drastic difference in the thermodynamic parameters between BumimTf2N and water was discussed in terms of the effect of solvation and electrostatic interactions in different media.