Syntheses and electrochemical characterization of heteroleptic cyclopentadienyl–dithiolene d2 tungsten complexes. Structures and magnetic properties of charge-transfer salts†

Abstract

Novel diamagnetic tungsten(IV) complexes of general formula W(η-C₅H₄R)₂(dithiolene) [R = H, SiMe₃ or Bu^t; dithiolene = C₃S₅^2– (4,5-disulfanyl-1,3-dithiole-2-thionate), C₃OS₄^2– (4,5-disulfanyl-1,3-dithiole-2-onate) or dddt^2– (5,6-dihydro-1,4-dithiine-2,3-dithiolate)] have been synthesized and their redox properties investigated by cyclic voltammetry. Two reversible oxidation waves are observed for each complex. The redox half-wave potentials allow [W(cp)₂(dddt)] (cp = η-C₅H₅) to react with the organic acceptor tcnq (tetracyanoquinodimethane) while the C₃S₅^2– and C₃OS₄^2– compounds reduce tcnqf₄ (7,7,8,8-tetracyano-1,2,4,5-tetrafluoroquinodimethane). X-Ray crystallographic studies were carried out on [W(cp)₂(dddt)]^˙+[tcnq]^˙– and [W(η-C₅H₄Bu^t)₂(C₃S₅)]^˙+[tcnqf₄]^˙–. The structural analyses and extended-Hückel calculations showed that the radical anions are strongly dimerised into diamagnetic moieties. The cations form centrosymmetrical dimers and exhibit antiferromagnetic interactions, as deduced from the temperature dependence of the magnetic susceptibility, with T(χ_max) = 18 and 22 K for [W(cp)₂(dddt)]^˙+[tcnq]^˙– and [W(η-C₅H₄Bu^t)₂(C₃S₅)]^˙+[tcnqf₄]^˙– respectively.