Cation concentration and local ligand field of polyether–salt complexes

Picturing the ion-chain local configuration of polyether–salt materials as forming oxygen-lined helical turns, with the cation located within the polymer cavity, the local environment of each cation is described in terms of a first coordination shell, characterized by the cation and by its nearest oxygen ligands. The interaction energy between nearest shells, ε, for the eutectic concentration of europium-based poly(ethylene oxide), PEO, electrolytes, is calculated by two separate processes: One relating the empirical value of the nearest-ligands local-field energy with the variation of Eu3+ concentration, n, and the other involving a two-electron polarization potential. This last procedure, besides determining the minimum intershells distance for the eutectic phase, permits the number of Eu3+–nearest oxygens to be fixed. The value obtained by the first procedure was ε=554.2 cm−1; while by the second, were ε=520.3 cm−1, for 10 nearest oxygens, and ε=572.4 cm−1, for 11 oxygens, for a mean radius of the first coordination shell R̄=2.4 Å and a minimum distance between nearest shells R0=5.3 Å. This model of chains of interacting coordination shells is extended to other polyether–salt complexes modified by mono and divalent cations. The corresponding two-electron interaction potential is calculated for a few monovalent-based crystalline PEO, complexes, while for noncrystalline divalent electrolytes only an upper limit is estimated.