Crystal Structures of Poly(Ethylene Oxide)3:LiBF4 and (Diglyme)n:LiBF4 (n = 1,2)

The crystal structures of PEO3:LiBF4, (diglyme)2:LiBF4, and (diglyme):LiBF4 have been determined and are compared. The helical conformation of each polymer chain and the stacking of neighboring chains in the structure of the PEO complex is similar to that found in the complexes with Li imide and Li triflate salts of the same PEO:salt ratio. Both PEO3:LiBF4 and (diglyme):LiBF4 have similar coordination around Li+, i.e., 3 ether oxygens and 2 fluorines from two BF4- anions. However, in the former each anion bridges two neighboring Li+ cations located along the PEO chain axis forming a continuous chain −BF4-−Li+−BF4-−Li+− whereas in (diglyme):LiBF4 two BF4- anions bridge between pairs of Li+ forming discrete diglyme−Li+−(BF4-)2−Li+−diglyme units that are linked to their neighbors predominantly by van der Waals bonding. The (diglyme)2:LiBF4 structure is compared with those of PEO6:LiSbF6 (no PEO6:LiBF4 exists) and (diglyme)2:LiSbF6. In both cases the Li+ cations are 6-coordinated by three ether oxygens from t...