Spectroscopic study of poly(ethylene oxide)6:: LiX complexes (X = PF6, AsF6, SbF6, ClO4)

The infrared and Raman spectra of the poly( ethylene oxide) chains in the complexes P(EO)(6)LiX (X = PF6, AsF6, SbF6, ClO4) are very similar although the conformational sequences of these chains are known to be different in the first three complexes. It seems that the leading factors in determining the common vibrational signature are the isostructural character of these complexes and their similar coordination of the lithium ion by two oxygens of one chain and three oxygens of a second chain. The P(EO)(6)-LiClO4 complex is confirmed to adopt a similar structure as the former three at room temperature even if its degree of crystallinity is lower. In its molten state, an equilibrium between free ions and contact ion-pairs is clearly evidenced by Raman spectroscopy. In the complexes P(EO)(3)LiX complexes at 25degreesC, PEO exhibits also a unique and specific spectral signature which seems to be characteristic of the P(EO)(3)-LiSO3CF3 type of structure, with the lithium ion coordinated by three oxygens of a PEO chain and two anions.