The anion ClO4- and the ion pair of Li+ClO4- have been studied by ab initio quantum chemical methods. Optimized geometries for monodentate, bidentate, and tridentate structures have been determined up to the MP2/6-311+G* level of theory. Vibrational frequencies were determined for the ClO4- anion and the Li+ClO4- ion pair up to the HF/6-311+G* level of theory. Comparisons are made with experimental Raman spectra of electrolyte solutions. At the highest level of theory, the bidentate structure was found to be preferred over monodentate or tridentate configurations.