X-ray powder diffraction patterns revealed that 1',1'''-diheptyl- and 1',1'''-dioctyl-1,1 "-biferrocenium triiodides obtained from he,vane and from dichloromethane have a layered structure with longer interlayer distances. 1',1'''-Diheptyl-1,1 "-biferrocenium triiodide falls under the category reported before, while 1', 1'''-dioctyl-1,1 " biferrocenium triiodide becomes exception; it shows a valence detrapping with increasing temperature despite the longer interlayer series. The difference in the crystal structure between longer and shorter interlayer distance series was reflected in the difference of the space group, 1',1'''-Diheptyl-1,1(")-bifenocenium triiodide (C34H46-Fe2I3) crystallizes in the monoclinic space group P2(1)/c with unit cell parameters a = 27.209(10) Angstrom, b = 9.6480(6) Angstrom, c = 14.012(10) Angstrom beta = 98.572(4)degrees, and Z = 4, while 1',1'''-dioclyl-1,1 "-biferrocenium triiodide (C36H50Fe2I3) crystallizes in the monoclinic space group P2(1)/c with a = 20.758(6) Angstrom, b = 9.80(1) Angstrom, c = 37.88(2) Angstrom beta = 90.44(3)degrees, and Z = 8. Both salts in the present study have a space group of P2(1)/c, which is different from the shorter interlayer series; 1',1'''-dihexyl- and 1',1'''-didodecyl-1,1 "-biferrocenium triiodides have a space group of P (1) over bar. The difference in the structure between the 1',1'''-diheptyl derivative and the 1',1'''-dioctyl derivative is also discussed. There is a difference in the symmetry of the monocation between the two salts, while both show the unsymmetrical triiodide anion. The difference between them makes the difference of the cation-cation interaction. The structure of the cations agrees with the result of Fe-57 MBssbauer spectroscopy. The cation-cation interaction in the stacking is observed in 1',1'''-dioctyl derivative, while such interaction is disturbed by the adjacent stacking in 1',1'''-diheptyl derivative.