Theoretical studies on blue versus red shifts in diglyme-M+-X− (M=Li, Na, K and X=BF4, ClO4, SCN)

Ab initio Hartree Fock calculations have been used to obtain the electronic structure and the frequencies of normal vibrations in the 1:1:1 solid polymer electrolytes CH3(OCH2CH2)2OCH3-M+-X− (M=Li, Na and K) (X=BF4, ClO4, SCN). The calculations predict stronger binding for the lithium ion towards the ether oxygens of diglyme in these electrolytes. Consequences of diglyme-MX interactions to the infrared spectra have been presented. Natural bond analysis and the electron density topography have been used to explain the direction of the frequency shifts of characteristics normal vibrations of the anion in these electrolytes. Local coordination of the metal ion with ether oxygens is relatively insensitive to the presence of counter-anion (BF4−, ClO4−or SCN−).