Multistability in a family of DT–TTF organic radical based compounds (DT–TTF)₄[M(L)₂]₃ (M = Au, Cu; L = pds, pdt, bdt)

The preparation of new charge transfer salts based on the DT–TTF donor and monoanionic square planar transition metal bisdichalcogenide complexes M(L)₂ (M = Au, Cu; L = pds, pdt, bdt, where pds = pyrazine-1,2-diselenolate, pdt = pyrazine-1,2-dithiolate, bdt = benzene-1,2-dithiolate) are reported and these salts are characterized by X-ray diffraction, EPR spectroscopy, electrical conductivity, thermoelectric power and static magnetization measurements, as well as tight-binding band structure calculations. Three compounds, (DT–TTF)₄[Au^III(bdt)₂]₃, (DT–TTF)₄[Cu^III(pds)₂]₃, (DT–TTF)₄[Cu^III(pdt)₂]₃, are members of a general family of compounds of DT–TTF with stoichiometry 4 : 3 as the previously reported (DT–TTF)₄[Au^III(pds)₂]₃. Although not strictly isostructural, all members of this family present a similar crystal packing motif of the donor and acceptor units and present a common pattern of first- and second-order phase transitions as seen in electrical transport and magnetic properties. The second-order phase transition is ascribed to a variation from dynamic to static charge ordering. With [Cu^III(pdt)₂] and DT–TTF a 1 : 1 salt with formula (DT–TTF)[Cu^III(pdt)₂] was also obtained. The structural differences and similarities between the four compounds (DT–TTF)₄[M(L)₂]₃ (M = Au, Cu; L = pds, pdt, bdt), that are related to their physical properties, and the reversible phase transitions observed are discussed.