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

Abstract

Metal bis­(dithiolene) complexes are promising building blocks for electrically conductive coordination polymers. N-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)2]− and [Cu­(qdt)2]2– (qdt2–: 6,7-quinoxalinedithiolate), as well as the 2D coordination polymer Cu­[Cu­(Hqdt)­(qdt)] (3). The dithiolene complexes were isolated as (Bu4N)2[Cu­(qdt)2] (1), Na­[Cu­(qdt)2]·4H2O (2a), [Na­(acetone)4]­[Cu­(qdt)2] (2b), and [Ni­(MeOH)6]­[Cu­(qdt)2]2·2H2O (2c). 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 3 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 [CuII(Hqdt)­(qdt)]− units link trigonal planar copper­(I) atoms to a dense 2D coordination polymer. The electrical conductivity of 3 at room temperature is 2 × 10–7 S/cm. Temperature dependent conductivity measurements confirm the semiconducting behavior of 3 with an Arrhenius derived activation energy of 0.33 eV. The strong absorption of 3 in the visible and NIR regions of the spectrum is caused by the small optical band gap of E g,opt = 0.65 eV, determined by diffuse reflectance spectroscopy. This study sheds light on the coordination chemistry of N-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.

Conductivity and photoconductivity in a two-dimensional zinc bis(triarylamine) coordination polymer

“…[2][3][4] A few examples of conductive 2D C. P. with a single crystal structure exist. [5][6][7] Most are obtained as crystalline powders. 2,3,[8][9][10][11] The lack of single crystal structures has restrained our knowledge of structure-property relationships with atomic precision.…”

Synthesis and coordination behaviour of 1H-1,2,3-triazole-4,5-dithiolates

“…In the course of our studies with sulphur-substituted alkynes we realized that a 1,3-dipolar coupling with azides would open a facile access to triazole dithiolate ligands, which to the best of our knowledge have not been described yet. In contrast, dithiolene ligands with ring fused six-membered aromatic rings bearing N donor centres (pdt 2− : pyrazine-2,3-dithiolate, 17,18–20 qdt 2− : quinoxaline-6,7-dithiolate, 21 and phendt 2− : phenanthroline-5,6-dithiolate, 22 Chart 1) were already utilized as conjugated bridging ligands. In particular, pyrazine-5,6-dithiolate have already shown promising results in the assembly of electrically conductive coordination polymers.…”