Structure and staging in polyacetylene charge-transfer complexes

A structure is proposed for a stage-2 complex of polyacetylene which contains potassium as the dopant ion. This structure utilizes as a basic motif an alkali-metal column surrounded by four polyacetylene chains; this motif is also found in the tetragonal phase that appears at higher dopant concentrations. In the new structure, each polyacetylene is adjacent to one alkali-metal column, so the phase contains four polymer chains per alkali-metal column as compared with two chains per column for the tetragonal phase. X-ray diffraction and electrochemical data show that a mixture of undoped and doped phases are present at low dopant concentrations. In light of these results, general aspects of staging in n-doped and p-doped polyacetylene are discussed.