UV VISIBLE SPECTROSCOPY STUDIES OF NI(II) COORDINATION IN POLY(ETHYLENE GLYCOL)

Electrolyte solutions formed by low-molecular-weight poly(ethylene glycol) (PEG) are model systems for understanding the ion-ion and ion-polymer bonding in high-molecular-weight, poly(ethylene oxide)-based solid polymer electrolytes. The electronic absorption spectra of Ni(II) in solutions of NiBr2 in PEG were analyzed to obtain information about the Ni(II) coordination environment. The results show that Ni(II) is partitioned between octahedral and tetrahedral complexes. The former are likely to be of the type [NiO6]2+ or a variation which includes Br(-I) ions. They represent Ni(II) trapped by association with the polymer chains. The latter appear to be free Ni(II) in the form of [NiBr4]2- complex ions. The equilibrium between the two Ni(II) forms shifts with salt concentration and can be correlated with changes in the viscosity and ionic conductivity of the electrolytes.