Abstract: The structures of ion-associated species between Na⁺, Li⁺, Mg²⁺ ions and ClO₄^-, NO₃^- were optimized via ab initio calculations. The influences of the cations to the ν₁-frequencies were also investigated and compared with those in SO₄^2- system. For the ion-associated structures, when the numbers of metal ions are not more than 2, the systems of ClO₄^- and NO₃^- are analogous to the SO₄^2- system. That is, the bidentate associated structures are easy to form between the anions and cations. When the numbers of metal ions are more than 2, especially for the clusters with more Mg²⁺ ion which has more positive charge, the repulsions between metal ions will make the clusters instable in the ClO₄^- and NO₃^- systems, while more monodentate structures will form in the SO₄^2- system. The influences of metal ions to the ν₁-frequencies of all three anions are similar, which can confirm the changes of frequencies in unhydrated clusters are less influenced by the characteristic of anion but more by the polarization of cation and associated structures.

Key words: Quantum chemical computation, Ion-associated species, Associated structure, ν₁-Frequency