SYNTHESIS, CRYSTAL-STRUCTURE AND SPECTROSCOPIC STUDIES OF NEW CHARGE-TRANSFER COMPOUNDS DERIVED FROM THE ORGANIC DONOR MOLECULE TETRATHIAFULVALENE, TTF, AND INORGANIC POLYOXOANIONS [M6O19]2-, WHERE M = MO, W

Tetrathiafulvalene, TTF, radical cation salts of polyoxoanions, [M6O19]2-, where M = Mo, W, have been isolated and characterised. (TTF)3[Mo6O19] has been synthesised by an electrochemical technique. Its crystal structure has been solved and it consists of a 1D stack of the donor TTF molecule, which fits into channels formed by the anions. Within the stack, a chain of trimers is identified, the inter-trimeric distance being 3.51 angstrom. The TTF molecules inside the trimer show a <> arrangement, with two different degrees of oxidation, the external being +0.5 and the central one +1. The IR, electronic and XPS spectra suggest the compound is a localised mixed-valence salt. The single-crystal electrical conductivity at room temperature has been found to be sigma = 10(-4) OMEGA-1 cm-1. Compounds corresponding to the chemical formula (TTF)2[M6O19], where M = Mo, W, have also been isolated and the crystal structures of both solved. They consist of isolated (TTF+.)2 dimers, interspersed with the polyoxoanions. In agreement with the crystal structure they are diamagnetic insulators. The spectroscopic properties of all these compounds are interpreted and discussed on the basis of their structural organisation.