Synthesis, molecular structure and supramolecular chemistry of a new nickel-quinoxaline dithiolate system [Bu₄N]₂[Ni(6,7-qdt)₂] (6,7-qdt = quinoxaline-6,7-dithiolate) and comparison of its electronic and electrochemical properties with those of [Bu₄N]₂[Ni(qdt)₂] (qdt = quinoxaline-2,3-dithiolate)

Abstract

The new nickel bis(dithiolene) complex [Bu₄N]₂[Ni(6,7-qdt)₂] (1) (6,7-qdt = quinoxaline-6,7-dithiolate) has been synthesized, starting from quinoxaline-6,7-dithiol, nickel chloride and tetrabutylammonium bromide in methanol. Compound 1 crystallizes in P2₁/c space group (monoclinic system). Its crystal structure has been characterized by interesting C— H···S and C— H···N weak interactions resulting in a three dimensional supramolecular network. Complex 1 shows solvent sensitive absorption band (broad feature) in the visible region, which is attributed to charge transfer (CT) transition involving electronic excitation from a HOMO that is a mixture of dithiolate (Π) and metal (d) orbital character to a LUMO which is a Π^* orbital of the dithiolate. This CT transition absorbs at low energy region in comparison to the CT band of the [Bu₄N]₂[Ni(qdt)₂] in the visible region. Interestingly, compound 1 undergoes reversible oxidation at very low oxidation potential (E_1/2 = + 0.12 V vs Ag/AgCl) compared to that of [Ni(qdt)₂]^2- (E_1/2 = + 0.41 V vs Ag/AgCl) in MeOH solutions.