The structure of metallic complexes of polyacetylene with alkali metals

Abstract

The crystal structures of sodium,potassium,rubidium, and cesium doped polyacetylene have been determined using crystal packing and x‐ray diffraction analyses. Each of these metallic complexes is tetragonal, with the polyacetylene chains forming a host lattice in which the alkali metal ions are present in channels. Lithium appears to be too small to stabilize the channel structure and an amorphous structure is observed. Predicted unit cell parameters and x‐ray diffraction intensities are in agreement with observed values. Similarities with the alkali metaldopedgraphite suggest that hybridization between carbon p z orbitals and metals orbitals occurs. Such hybridization is expected to result in a high conductivity component normal to the chain direction. On the other hand, direct overlap between polymer chains appears small, since alkali metal columns separate polymer chains. Compositions calculated for the channel structures (from meridional diffraction spacings, the intensity of equatorial diffraction lines, measured volume expansion, and distances in model complexes) all range from y=0.12 to 0.18 for (CHM y ) x , where M is sodium,potassium,rubidium, or cesium.