The compound [Ni(QM)2], QM = 4,6-di-tert-butyl-N-(2-methylthiomethylphenyl)-o-iminobenzoquinone, is a singlet diradical species with approximately planar configuration at the tetracoordinate metal atom and without any Ni-S bonding interaction. One-electron oxidation results in additional twofold Ni-S coordination (dNi-S ≈2.38 Å) to produce a complex cation of [Ni(QM)2](PF6) with hexacoordinate Ni(II) and two distinctly different mer-configurated tridentate ligands. The O,O'-trans arrangement in the neutral precursor is changed to an O,O'-cis configuration in the cation. The EPR signal of [Ni(QM)2](PF6) has a very large g anisotropy and the magnetic measurements indicate an S = 3/2 state. The dication was structurally characterized as [Ni(QM)2](ClO4)2 to exhibit a similar NiN2O2S2 framework as the monocation. However, the two tridentate (O,N,S) ligands are now equivalent according to the formulation [Ni(II)(QM(0))2](2+). Cyclic voltammetry reflects the qualitative structure change on the first, but not on the second oxidation of [Ni(QM)2], and spectroelectrochemistry reveals a pronounced dependence of the 800-900 nm absorption on the solvent and counterion. Reduction of the neutral form occurs in an electrochemically reversible step to yield an anion with an intense near-infrared absorption at 1345 nm (ε = 10,400 M(-1)  cm(-1)) and a conventional g factor splitting for a largely metal-based spin (S = 1/2), suggesting a [(QM(·-))Ni(II)(QM(2-))](-) configuration with a tetracoordinate metal atom with antiferromagnetic Ni(II)-(QM(·-)) interactions and symmetry-allowed ligand-to-ligand intervalence charge transfer (LLIVCT). Calculations are used to understand the Ni-S binding activity as induced by remote electron transfer at the iminobenzoquinone redox system.

Complexes [Ru(bpy-R)(2)(NCS)(2)], where R = H (1), 4,4'-(CO(2)Et)(2) (2), 4,4'-(OMe)(2) (3), and 4,4'-Me(2) (4), were studied by spectroelectrochemistry in the UV-vis and IR regions and by in situ electron paramagnetic resonance (EPR). The experimental information obtained for the frontier orbitals as supported and ascertained by density functional theory (DFT) calculations for 1 is relevant for the productive excited state. In addition to the parent 1, the ester complex 2 was chosen for its relationship to the carboxylate species involved for binding to TiO(2) in solar cells; the donor-substituted 3 and 4 allowed for better access to oxidized forms. Reflecting the metal-to-ligand (Ru → bpy) charge-transfer characteristics of the compounds, the electrochemical and EPR results for compounds 1-4 agree with previous notions of one metal-centered oxidation and several (bpy-R) ligand-centered reductions. The first one-electron reduction produces extensive IR absorption, including intraligand transitions and broad ligand-to-ligand intervalence charge-transfer transitions between the one-electron-reduced and unreduced bpy-R ligands. The electron addition to one remote bpy-R ligand does not significantly affect the N-C stretching frequency of the Ru(II)NCS unit. Upon oxidation of Ru(II) to Ru(III), however, the single N-C stretching band exhibits a splitting and a shift to lower energies. The DFT calculations serve to reproduce and understand these effects; they also suggest significant spin density on S for the oxidized form.

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The cyclic alkyl(amino) carbene (cAAC) stabilized biradicals of composition (cAAC)SiH (1), (cAAC)SiMe-SiMe(cAAC) (2), and (cAAC)SiMeCl-SiMeCl(cAAC) (3) have been isolated as molecular species. All the compounds are stable at room temperature for more than 6 months under inert conditions in the solid state. All radical species were fully characterized by single-crystal X-ray structure analysis and EPR spectroscopy. Furthermore, the structure and bonding of compounds 1-3 have been investigated by theoretical methods. Compound 1 contains the SiH moiety and this is the first instance, where we have isolated 1 without an acceptor molecule.

Schritt für Schritt: Für die H2‐entwickelnde Oxidation eines Dicarbonylcobalthydrid‐Komplexes mit dem sterisch abschirmenden 1,1′‐Bis(diisopropylphosphanyl)ferrocen‐Liganden lassen sich Elektronen‐ und Wasserstoff‐Übertragungsschritte IR‐spektroelektrochemisch und strukturell dokumentieren. Die Reaktionssequenz komplementiert den für Wasser‐reduzierende Cobaltverbindungen mit weniger stark π‐akzeptierenden Liganden diskutierten Mechanismus.