About the abnormal Valence of the Transition Metal in The CT complex

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Bis (ethylenedithio) tetrathiafulvalene (BEDT-TTF) forms many charge transfer complexes. The crystal of (BEDT-TTF)_4 [Ni(CN)_4] belongs to the triclinic pl with the lattice constants of a=10.994 (2), b=16.443 (2), c=9.703 (1), alpha=97.85 (1), beta=115.15 (1), gamma=95.94 (1)ﾟ. In the crystal, there exists the face to face overlap of the BEDT-TTF molecules along the [201] direction. The intermolecular interaction by the short S ・・・ S contact is also observed along the [201] direction.The room temperature conductivity was about 20S/cm. The crystal was metellic between 230 and 300K and became semi-conductive with an energy gap of 100K below 160K, although the temperature dependence of the conductivity was not obtween 160 and 230K. This kind of resistance behavior may be explained by the phase transition of the crystal between 160 and 230K.The ESR spectrum at 4K consists of the strong band at g=2.013 and the weak band at g=2.056.