PREPARATION, X-RAY CRYSTAL-STRUCTURE AND SPECTRAL INVESTIGATION OF THE PENTAMERIZED TTF ION-RADICAL SALT - (TTF)5[PT(CN)4]2(CH3CN)2

Crystals of (TTF)5[Pt(CN)4]2(CH3CN)2 obtained electrochemically have b een shown to be to better quality than those obtained by the diffusion method. More accurate X-ray crystal structure analysis and optical in vestigations are performed. The presence of a mixed-valence state is a rgued from the charge-transfer band absorbance at 5850 cm-1, in spite of a measured room temperature d.c. conductivity of only 10(-5) OMEGA- 1 cm-1. The optical properties are interpreted in terms of a model tha t includes electron-molecular vibration coupling and an extended Hubba rd Hamiltonian for centrosymmetrical isolated pentamers with four hole s each.