EXAFS STUDIES OF MIXED SALT COBR2 LIBR-PEO COMPLEXES/

X-ray absorption spectroscopy at the Co K edge was used to study the C o coordination in CoBr2 (PEO)(16) and [0.45 CoBr2 + 0.55 LiBr](PEO)(16 ) at 25 degrees C. In CoBr2 (PEO)(16) the salt consists of mostly undi ssociated CoBr2 coordinated with six oxygens from the PEG. The respect ive Co-Br and Co-O bond lengths are 2.36 Angstrom, and 2.49 Angstrom. In [0.45 CoBr2 + 0.55 LiBr](PEO)(16) the Co is coordinated with three Br atoms with a bond distance of 2.40 Angstrom and between two and thr ee O atoms with a bond distance of 2.27 Angstrom. On the addition of L iBr the Co coordination changes from a mixture of octahedral and tetra hedral species to exclusively tetrahedral coordination. The anomalous conductivity behaviour of the mixed salt CoBr2/LiBr-(PEO) complex is r elated to the formation of CoBr3- complexes and a reduction in crossli nking of the PEO by the CoBr2.