The redox properties of copper, nickel, and cobalt complexes (MePh 3 P)[M(bdt) 2 ] with the ligand benzene-1,2-dithiolate (bdt) and synthesized complexes (MePh 3 P)[M(bdtCl 2 ) 2 ] with the ligand 3,6-dichlorobenzene-1,2-dithiolate (bdtCl 2 ) have been studied by cyclic voltammetry and in situ EPR−UV/vis/NIR spectroelectrochemistry. The addition of chlorine substituents to the 3-and 6-positions of the benzene ring not only facilitates the reduction of [M(bdtCl 2 ) 2 ] − complexes but also leads to the remarkable stabilization of [M(bdtCl 2 ) 2 ] 2− dianions in solution. In contrast to the EPR-silent copper complexes, the solutions of nickel samples exhibit a broad singlet EPR signal at room temperature which becomes anisotropic at 100 K with a characteristic rhombic pattern. Cathodic reduction of copper and cobalt complexes leads to paramagnetic species having an EPR signal with splitting from 63,65 Cu for copper and from 59 Co for cobalt samples, confirming a strong contribution of the central atom with substantial delocalization of the unpaired spin onto the central atom. B3LYP/6-311g*/pcm calculations of the monoanions as well as of their oxidized and reduced forms were performed. The spin density of all open-shell ground states calculated for the investigated complexes in different redox states corresponds well to the experimental spectroelectrochemical data.

Template condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde S-methylisothiosemicarbazone with pentane-2,4-dione and triethyl orthoformate at elevated temperature resulted in metal complexes of the type MIIL, where M = Ni, Cu and H2L = novel tetradentate organic ligand. These complexes are relevant to the active site of the copper enzymes galactose oxidase and glyoxal oxidase. Demetallation of NiIIL with gaseous hydrogen chloride in chloroform afforded the metal-free ligand H2L. Then by the reaction of H2L with Zn(CH3COO)2·2H2O in 1:1 molar ratio in chloroform/methanol 1:2 the complex ZnIIL(CH3OH) was prepared. The three metal complexes and the prepared ligand were characterized by spectroscopic methods (IR, UV–vis and NMR spectroscopy), X-ray crystallography and DFT calculations. Electrochemically generated one-electron oxidized metal complexes [NiL]+, [CuL]+ and [ZnL(CH3OH)]+ and the metal-free ligand cation radical [H2L]+• were studied by EPR/UV–vis–NIR and DFT calculations. These studies demonstrated the interaction between the metal ion and the phenoxyl radical.

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The redox behavior of the series of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f]quinolines with R(7), R(8) = H, COOC(2)H(5), COOCH(3), COOH, COCH(3), and CN has been studied by in situ EPR and EPR/UV-vis spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigma-dimer (σ-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV-vis cyclovoltammetric experiments. The site of the dimerization in the σ-dimer and the mapping of the unpaired spin density both for radical anions and σ-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.

DFT = density functional theory,P ROXYL = 2,2,5,5-tetramethyl-1-pyrrolidinyloxy,TEMPO = 2,2,6,6-tetramethyl-1-piperidinyloxy.Supporting informationfor this article can be found under: https://doi.

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Turning on and off associations between molecules by a reversible change in their redox states is a convenient way of controlling self‐assembly and hence for advancing supramolecular chemistry. Here we present systematic studies on a selection of extended tetrathiafulvalenes with thienoacene spacers. By cyclic and differential pulse voltammetry and in situ EPR/UV‐Vis‐NIR spectroelectrochemistry, in combination with computations, we have elucidated how the number and orientations of thiophene rings in the spacer between the two dithiafulvene rings influence both the donor strength and association properties. The radical cations and their associates were found to cover a remarkable large region of the UV‐Vis‐NIR spectrum, but the appearance of the absorption spectrum of the radical cations as well as of the unassociated dications also depended strongly on the exact molecular structure.