Theoretical insights into PF6− and its alkali metal ion pairs: geometries and vibrational frequencies

The structures, vibrational frequencies, infrared and Raman intensities of hexafluorophosphate anion (PF6−) and M+PF6− (M+ = Li+, Na+, K+, Rb+ and Cs+) ion pairs have been studied by ab initio calculations. It is shown that the tridentate coordination of cation by PF6− is the most stable structure in gas phase. The vibrational spectroscopies of the most stable geometries were calculated and the changes in band position were used to probe the ion associations.