Location of a divalent cation absorbed in an anodically produced crown-ether polymer

Abstract

The structure of poly(dibenzo-18-crown-6) complexed with the divalent cation Sr²⁺ has been examined by extended X-ray absorption fine structure (EXAFS) spectroscopy in order to study what influence the electrical charge on the cation has on the interaction between the complexed cation and the heteroatoms of the polymer framework. The Sr²⁺ ion is found to be situated at the centre of the crown formed by six oxygen and 12 carbon atoms. It is shown that the local structural environment of the Sr²⁺ ion consists of 4 Sr–O bonds of length 2.512 Å and two slightly longer Sr–O bonds of length 2.639 Å. This work confirms our earlier findings, where it was shown that the monovalent cations Ag⁺ and Cs⁺ also sit at the centre of the polymer crown. This work also indicates that the localised structure surrounding these cations is the same irrespective of whether the complex is in the monomeric or polymeric form.