Proton and Electron Transfer in the Formation of a Copper Dithiolene-Based Coordination Polymer.

Metal bis(dithiolene) complexes are promising building blocks for electrically conductive coordination polymers. -Heterocyclic dithiolene complexes allow their cross-linking via the coordination of N-donor atoms to additional transition metal ions. In this study, we present the formal copper(II) and copper(III) 6,7-quinoxalinedithiolene complexes [Cu(qdt)] and [Cu(qdt)] (qdt: 6,7-quinoxalinedithiolate), as well as the 2D coordination polymer Cu[Cu(Hqdt)(qdt)] (). The dithiolene complexes were isolated as (BuN)[Cu(qdt)] (), Na[Cu(qdt)]·4HO (), [Na(acetone)][Cu(qdt)] (), and [Ni(MeOH)][Cu(qdt)]·2HO (). Their crystal structures reveal nearly planar complexes with a high tendency of π-stacking. For a better understanding of their coordination behavior, the electronic properties are investigated by UV-vis-NIR spectroscopy, cyclic voltammetry, and DFT simulations. The synthesis of the 2D coordination polymer involves the reduction and protonation of the monoanionic copper(III) complex. A combination of powder X-ray diffraction, magnetic susceptibility measurements, as well as IR and EPR spectroscopy confirm that formal [Cu(Hqdt)(qdt)] units link trigonal planar copper(I) atoms to a dense 2D coordination polymer. The electrical conductivity of at room temperature is 2 × 10 S/cm. Temperature dependent conductivity measurements confirm the semiconducting behavior of with an Arrhenius derived activation energy of 0.33 eV. The strong absorption of in the visible and NIR regions of the spectrum is caused by the small optical band gap of = 0.65 eV, determined by diffuse reflectance spectroscopy. This study sheds light on the coordination chemistry of -heterocyclic dithiolene complexes and may serve as a reference for the future design and synthesis of dithiolene-based coordination polymers with interesting electrical and magnetic properties.