Physical and structural properties of organomineral conductors: TTF radical cation salts with metal halides

A series of tetrathiafulvalene radical cation salts with unusual 2d organization have been prepared by electrochemistry, involving different dianions of metal chlorides as counter-ions. These mixed-valence compounds are semiconductors with a complex stoichiometry which has been established by a room temperatre crystal structure determination. Except for the cadmium chloride compound, they appear to be isomorphous and behave like (TTF)14(CoCl4)4. This salt is monoclinic C2/m with two presumably neutral TTF and two inequivalent pairs of trimers. The optical properties are in agreement with this peculiar structural organization. By polarized reflectivity and absorption experiments, the authors observed a plasma edge around 8000 cm-1 and a C.T. band with doublets of IR vibronic lines. This is due to different electron-molecular vibration coupling inside each trimer.