Lanthanide-Nitrate Interaction in Anhydrous Acetonitrile and Coordination Numbers of the Lanthanide Ions: FT-IR Study

Article abstract of DOI:10.1002/hlca.19930760316

The interaction between lanthanide ions Ln^III (Ln = La, Nd, Sm-Dy, Er, Yb) and nitrate ions is investigated by FT-IR spectroscopy in dilute anhydrous MeCN solution.The work is performed for ratios R = _t/III>_f ranging from 0 to 8 and for solutions generally 0.05 M in Ln^III, prepared from anhydrous lanthanide perchlorates Ln(ClO4)3.When nitrate is progressively added to the Ln(ClO4)3 solutions, the formation of n>^(3-n)+ species is clearly evidenced by the FT-IR spectra.All the NO3(1-) ions are coordinated and bidentate.A quantitative study was performed using the v₁ and v₆ vibrational modes for coordinated NO3(1-) ions.The average coordination numbers estimated for Nd, Eu, Tb, and Er in solutions of trinitrates are 9.0, 9.1, 8.3, and 8.2, respectively ( +/- 0.3 unit).In presence of an excess NO3(1-), these numbers become 9.8, 10.2, 10.0, 9.8, 9.9, and 9.9 (+/- 0.3 unit) for La, Nd, Eu, Tb, Er, and Yb, respectively.No hexanitrato species forms under the experimental conditions used (R up to 8).The structural aspect of the various nitrato species is also investigated.In the pentanitrato species, all the ligands appear to be equivalent, while large inequivalences are observed for Ln(NO3)3 solutions.Since for the latter most of the absorption bands assigned to nitrate vibrations contain several components, a curve-fitting procedure has been used for decomposing the v₂, v₄, and v₆ vibrations.There is a considerable difference between Ln^III ions, the nitrate inequivalences being larger in the middle of the series.