Vibrational Study of the Crystalline Phases of (CH3(OCH2CH2)2OCH3)2LiSbF6 and P(EO)6LiMF6 (M = P, As, Sb)

The structure of (CH 3 (OCH 2 CH 2 ) 2 OCH 3 ) 2 LiSbF 6 was solved by single-crystal X-ray diffraction techniques. The compound crystallizes in the orthorhombic Pccn space group with a unit cell containing four lithium ions, each of which is coordinated by two CH 3 (OCH 2 CH 2 ) 2 OCH 3 or diglyme molecules. The SbF 6 - anion does not directly interact with the cation, similar to its isolated environment in crystalline, high molecular weight P(EO) 6 LiSbF 6 . A comparative vibrational spectroscopic study of (CH 3 (OCH 2 CH 2 ) 2 OCH 3 ) 2 LiSbF 6 and P(EO) 6 LiSbF 6 demonstrated that the ethylene oxide vibrations in both systems were essentially decoupled and could be analyzed in terms of a single diglyme or PEO molecule, respectively. A spectroscopic comparison of the isostructural crystalline P(EO) 6 LiAsF 6, P(EO) 6 LiPF 6, and P(EO) 6 LiSb 6 compounds demonstrated that the band frequencies in the former compound are consistently higher by a few wavenumbers than those of the latter two systems. This was attributed to the effect of the Li−O distances.