Vibrational study of the crystalline phases of (CH3(OCH2CH2)(2)OCH3)(2)LiSbF6 and P(EO)(6)LiMF6 (M = P, As, Sb)

The structure of (CH3(OCH2CH2)(2)OCH3)(2)LiSbF6 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 CH3(OCH2CH2)(2)OCH3 or diglyme molecules. The SbF6- anion does not directly interact with the cation, similar to its isolated environment in crystalline, high molecular weight P(EO)(6)LiSbF6. A comparative vibrational spectroscopic study of (CH3(OCH2CH2)(2)OCH3)(2)LiSbF6 and P(EO)6LiSbF6 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)LiAsF6, P(EO)(6)LiPF6, and P(EO)(6)LiSb6 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.