Jean-Claude Bunzli - Ft-Ir and Fluorometric Investigation of Rare-Earth and Metal-Ion Solvation .10. Inner-Sphere Interaction Between Perchlorate and Lanthanide Ions in Anhydrous Acetonitrile

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  Bunzli,J.C.G., Kasparek,V. Inorganica Chimica Acta  1991 182 (1) 101-107

  Abstract: The interaction between perchlorate   and Ln(III) ions has been investigated in anhydrous acetonitrile   for Ln = La, Pr, Sm, Gd, Dy, Ho, Tm and Yb. Control experiments   have been carried out with Ln = Nd, Eu and Er. Vibrations   assigned to unassociated (u), monodentate (m) and bidentate (b)   perchlorate anions were identified in 0.05 M solutions of   Ln(ClO4)3. Quantitative FT-IR measurements allowed the   determination of the number of uncoordinated perchlorate ions,   ClO4-(u), per Ln(III) ion, n(u), which increases from 1.43 (La)   to 1.8-1.9 (Pr-Gd) and to 2.0-2.1 (Tb-Yb). Examination of other   parameters such as the value and the variation of the   nu-4(E)-nu-1(A1) and nu-8(B2)-nu-1(A1) splittings for ClO4-(m)   and ClO4-(b) ions, respectively, the area of vibrational bands   assigned to ClO4-(m), and the hypsochromic shift of vibrations   assigned to bonded acetonitrile molecules, leads to the following   interpretation. Both ClO4-(m) and ClO4-(b) ions are in the inner   coordination sphere and the quantitative data point to a   complicated situation in which several equilibria take place   between species differing by the number of coordinated   perchlorate ions, by the coordination mode of the perchlorate   ions, and, probably, by the number of coordinated acetonitrile   molecules. Changes in the average coordination number of the   Ln(III) ions occur between La and Pr and at Gd. The equilibrium   ratios for the formation of the monoperchlorato species could be   evaluated for the heavier lanthanides: log K1 ranges between 1.8   and 2.7. Water molecules replace bonded perchlorate ions in the   inner coordination sphere and so do chloride ions. The affinity   of Ln(III) ions for chloride ions relative to perchlorate ions   has been calculated to be log K(Cl/ClO4) = 1.1, 1.2 and 0.5 for   La, Nd and Er, respectively. Finally, an estimate of the   formation constant of the monochloro complex of Er yielded log   K(Cl) = 2.6 +/- 0.7

  Address (URL): WOS:A1991FQ48900016