The structures of c i s-polyacetylene and highly conducting derivatives

Abstract

The structures of cis‐polyacetylene and polyacetylene–iodine derivatives have been investigated by x‐ray diffraction and crystal packing analysis. Results obtained for cis‐polyacetylene are consistent with the space group Pnma with one CH per asymmetric unit and a chain symmetry (m1̄)_t. Hence, the structure is analogous to that of orthorhombic polyethylene. For a structure with such a concentration of π electrons there is minimal overlap between parallel π orbitals. The π orbitals are almost orthogonal for four of the six closest neighbors of a given chain. Based on x‐ray diffraction and spectroscopic results, a model is proposed for the structure of the highly conducting polyacetylene–iodine complexes. According to this model, linear arrays of polyhalide ions (principally in the form of I⁻₃) substitute in positions of displaced polyacetylene chains. At high dopant concentrations, alternate close‐packed layers of polyacetylene are separated by a layer consisting of such polyhalide arrays. This model predicts a limiting charge transfer of 0.11 electron on the average per carbon atom in the polyacetylene chain.