FT-IR investigation of the interaction between dimethylsulphoxide (DMSO) and some lanthanide nitrates in acetonitrile solutions

Abstract

The interaction of dimethylsulphoxide (DMSO) with neodymium, terbium and erbium nitrates is studied in dilute anhydrous acetonitrile solutions. The FT-IR difference spectra are measured for ratios R = [DMSO]t [Ln]t ranging from 0 to 6 and for [LnIII] = 0.05 M and the results are compared with those obtained previously for europium solutions. The nitrate ions remain coordinated in a bidentate fashion; dissociation occurs only if R > 9. Bound acetonitrile molecules are present up to R = 2.9 (europium, terbium, erbium) or 4.1 (neodymium). The number of coordinated DMSO molecules per LnIII ion has been determined by the molar ratio method applied to both the v7 (1008 cm-1) and v22 (716 cm-1) absorptions. For R = 6, the values are 3.6 (neodymium), 3.1 (europium), 3.0 (terbium) and 3.0 (erbium), which leads to the following average coordination numbers: 9.6 (neodymium), 9.1 (europium), 9.0 (terbium) and 9.0 (erbium). These coordination numbers depend upon the DMSO concentration. Between R = 2 and R = 6 equilibria take place between eight- and nine-coordinate species (europium, terbium, erbium, lg K9 = 1.8 ± 0.2) or nine- and ten-coordinate species (neodymium, lg K10 = 1.1 ± 0.2). © 1986.