Y. Chatani, Sigeru Okamura
Oct 1, 1987
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Polymer
Abstract
Abstract The crystal structure of poly(ethylene oxide)-sodium iodide (PEO-NaI) complex, a highly ionic conductor, was determined by the X-ray diffraction method. The crystals belong to the monoclinic system of space group P 2 1 a . The cell constants are a = 18.15 A , b = 8.41 A , c ( chain axis ) = 7.98 A and y = 122.3° (first setting). The molar ratio (EO:NaI) is 3:1, and there are 12 monomer units (two chains) and four NaI ion pairs in the unit cell. The crystal structure is characterized as follows: (1) The polymer chain, in which the asymmetric unit consists of three monomer units, takes a 2 1 helix of conformation (TTGTTGTTḠ)2 (T, trans; G and G, plus and minus gauche, respectively). (2) Na+ and I− ions are linked alternately to form a zigzag chain. (3) The NaI chain is coiled round by the helical polymer chain in such a way that a couple of NaI ion pairs makes the same repeat period to that of the polymer helix. (4) Each Na+ ion is coordinated by three polymer oxygen atoms and two I− ions.