Bis(quinoxaline‐dithiolato)nickel(III) Complexes [Bu4N][NiIII(6,7‐qdt)2] and [Ph4P]­[NiIII(Ph26,7‐qdt)2]·CHCl3 (6,7‐qdt = Quin­oxaline‐6,7‐dithiolate; Ph26,7‐qdt = Diphenylquinoxaline‐6,7‐dithiolate): Synthesis, Spectroscopy, Electrochemistry, DFT Calculations, Crystal Structures and Hirshfeld Surface Analysis

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.

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Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems

Amb

Heth

Evenson

et al. 2016

Inorg. Chem.

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A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings. The complexes exhibit tunable, intense near-IR (NIR) absorption in the range of 1076-1160 nm with molar absorptivity as high as 25100 M cm in solution. The electronic tunability as well as the desirable solid-state packing arrangements of these systems suggests significant potential as NIR-absorbing materials for optoelectronic applications.

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Cited by 3 publications

References 36 publications

Structure, spectroscopic properties and catalytic activity for epoxide ring-opening of nickel methylxanthate

Structure, spectroscopic properties and catalytic activity for epoxide ring-opening of nickel methylxanthate

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

Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems

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