Nickel dithiolenes containing pendant thiophene units: precursors to dithiolene–polythiophene hybrid materials

Abstract

The synthesis, electrochemical and spectroscopic properties of the new thiophene-substituted metal dithiolene complexes [Ni(b-3ted)₂] (3) and [NBu₄][Ni(b-3ted)₂] ([NBu₄][3]) are described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene] and compared with new studies of the known compounds [Ni(b-2ted)₂] (2) and [NBu₄][Ni(b-2ted)₂] ([NBu₄][2]). X-Ray structures were determined for the neutral complexes 2 and 3 and both showed planar nickel dithiolene units with thiophene groups twisted out of the molecular plane, precluding close molecular π-stacking. Electrochemical investigations revealed two redox processes corresponding to interconversion between neutral, monoanionic and dianionic species for 3, analogous to 2. Oxidation of 0.1 mM [3]⁻ in CH₃CN was shown to give a green molecular film of 3 which, in contrast to as-prepared crystals of 3, showed significant conductivity. Electrochemical polymerisation of 3 carried out at different concentrations resulted in films; electrochemical, SNIFTIRS and UV-Vis results were consistent with incorporation of the intact metal dithiolene complex in these films. In contrast, electrochemical polymerisation of 2 gave a film charateristic of a polymerised thiophene but with no evidence of incorporation of the intact metal dithiolene complex. Copolymerisation of 3 with thiophene gave a gold-coloured electropolymerised film of significant conductivity that, upon dissolution in CH₂Cl₂, showed the characteristic low energy absorption of the Ni-dithiolene complex, confirming its incorporation. This copolymerisation approach offers a versatile route to the synthesis of metal dithiolene–polythiophene hybrid films.