Theoretical studies in local coordination and vibrational spectra of M+CH3O(CH2CH2O)nCH3 (n = 2-7) complexes (M = Na, K, Mg and Ca)

Solid polymer electrolytes (SPE) comprised of poly(ethylene oxide) (PEO) oligomers complexed with alkali metal salt of weakly coordinating anions have been of a great interest due to their high ionic conductivity. Ion pair formation influence the number of charge carriers and is an important factor underlying the ion transport phenomenon. In this work, the electronic structure and vibrational spectra of the metal ion-PEO oligomer represented by M-CH3O(CH2CH2O)nCH3 (n = 2-7) (M = Na+, K+, Mg2+ and Ca2+) are obtained by employing the ab initio and hybrid density functional methods. Structural and spectral consequences of PEO oligomers to the alkali- and alkaline earth-metal ion coordination in different chemical environments have been presented. In metal ion-PEO oligomer ion-pairs the Mg2+ ion binds strongly to ether oxygens of polyether complexes. The density functional calculations predict the heptaglyme (n = 7 in the above series) binds strongly to the metal ion. The frequency shifts of characteristics vibrations induced by the metal ion-coordination in CH3O(CH2CH2O)nCH3-M (n = 2-7) complexes have been discussed.