Synthesis and physicochemical properties of charge transfer compounds derived from the reaction of tetrathiafulvalene with copper(II)

Charge transfer compounds with the general formula (TTF)(4)CuX2 (TTF=tetrathiafulvalene; X = NCS, NO3, Cl, Br, NCO and NO2) were prepared by the reaction of excess TTF with the precursor Cu(Sp)X-2[Sp = ()-sparteine] complexes in dichloromethane. The TTF radical patterns were observed in EPR spectra and a signal attributable to Cu(11) was not detected in the solid state for the prepared compounds, indicating that there is charge transfer from the TTF donors to the copper metal(11) ions and that the copper center in (TTF)(4)CuX2 is in a diamagnetic Cu(I) state. The powdered electrical conductivities of some (TTF)(4)CuX2 (X = NCS, NO3, Cl and Br) compounds are in the semiconductor region (sigma(r.t) = 10(0)-10(1) Scm(-1)), whereas the other compounds (X = NCO and NO2) are in the insulator range (sigma(r.t) < 10(-4) Scm(-1)) at room temperature. The electrical conductivities of the prepared six compounds are closely related to the charge transfer rate from TTF to Cu(Sp)X-2 in the formation of (TTF)(4)CuX2 and the reduction potential of the precursor Cu(Sp)X-2 complexes. (C) 2004 Elsevier Ltd. All rights reserved.