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)

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. 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- (qdt^2-: 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 [Cu^II(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.

Strategic design of thiophene-fused nickel dithiolene derivatives for efficient NLO response

The zwitterionic donor–acceptor group significantly reduces the HOMO–LUMO energy gap resulting in an enormous increase in the first hyperpolarizability values.

Solution, Solid, and Gas Phase Studies on a Nickel Dithiolene System: Spectator Metal and Reactor Ligand

The syntheses of cationic nickel complexes using N,N'-dimethyl piperazine 2,3-dithione (Me2Dt(0)) and N,N'-diisopropyl piperazine 2,3-dithione ((i)Pr2Dt(0)) ligands are reported. These ligands were used in synthesizing bis and tris(dithione)Ni(II) complexes as tetrafluoroborate or hexafluorophosphate salts, i.e., [Ni((i)Pr2Dt(0))2][BF4]2 ([1a][BF4]2), [Ni((i)Pr2Dt(0))2][PF6]2 ([1a][PF6]2), [Ni(Me2Dt(0))2][BF4]2 ([1b][BF4]2), [Ni((i)Pr2Dt(0))3][BF4]2 ([2a][BF4]2), and [Ni((i)Pr2Dt(0))3][PF6]2 ([2a][PF6]2), respectively. Complex [2a][PF6]2 was isolated from a methanolic solution of [1a][PF6]2. Compound [1a][BF4]2 crystallizes in a trigonal crystal system (space group, P31/c) and exhibits unique packing features, whereas [2a][BF4]2 crystallizes in a monoclinic (P21/n) space group. Cyclic voltammograms of [1a][BF4]2 and [1b][BF4]2 are indicative of four reduction processes associated with stepwise single-electron reduction of the ligands. Spectroelectrochemical experiments on [1a][BF4]2 exhibit an intervalence charge transfer (IVCT) transition as a spectroscopic signature of the mixed-valence [Ni((i)Pr2Dt(0))((i)Pr2Dt(1-))](-) species. Analysis of this IVCT band suggests that this ligand based mixed valence complex, [Ni((i)Pr2Dt(0))((i)Pr2Dt(1-))](-), behaves more like a traditional class II/III metal based mixed-valence complex. The density functional theory (DFT) and time dependent DFT calculations provide a theoretical framework for understanding the electronic structures and the nature of excited states of the target compounds that are consistent with their spectroscopic and redox properties. Vibrational spectra of [1a](2+) and [2a](2+) were investigated as discrete species in the gas phase using infrared multiple photon dissociation (IRMPD) spectroscopy.