Radical or Not Radical: Compared Structures of Metal (M = Ni, Au) Bis-Dithiolene Complexes with a Thiazole Backbone

A complete series of dianionic, monoanionic, and neutral dithiolene complexes formulated as [Ni­(Et-thiazdt)₂]^<i>n</i>, with <i>n</i> = −2, −1, 0, and Et-thiazdt: <i>N</i>-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate, is prepared using an optimized procedure described earlier for the N–Me derivatives. Electrochemical and spectroscopic properties confirm the electron-rich character of the Et-thiazdt dithiolate ligand. The three complexes are structurally characterized by single-crystal X-ray diffraction. The paramagnetic anionic complex [Ni­(Et-thiazdt)₂]⁻¹, as Ph₄P⁺ salt, exhibits side-by-side lateral interactions leading to a Heisenberg spin chain behavior. The solid-state structure of the neutral, diamagnetic [Ni­(Et-thiazdt)₂]⁰ complex shows a face-to-face organization with a large longitudinal shift, at variance with the structure of its radical and neutral gold dithiolene analogue described earlier and formulated as [Au­(Et-thiazdt)₂]^•. Comparison of the two structures, and those of the other few structurally characterized pairs of Ni/Au dithiolene complexes, demonstrates the important role played by overlap interactions between gold dithiolene radical species. Despite its closed-shell character, the neutral nickel complex [Ni­(Et-thiazdt)₂]⁰ exhibits a semiconducting behavior with a room-temperature conductivity σ_RT ≈ 0.014 S cm^–1

Efficient Hydrogen Production at pH 7 in Water with a Heterogeneous Electrocatalyst Based on a Neutral Dimeric Cobalt-Dithiolene Complex

The development of efficient hydrogen production technologies is fundamental for replacing fossil-fuel-based energies. As such, electrocatalysts derived from Earth-abundant metal complexes are appealing, and interesting performances have typically been disclosed under acidic conditions in organic solvents. However, their applicability under relevant pH-neutral conditions has been underexplored. Herein, we demonstrate that nonionic, dimeric cobalt-dithiolene complexes supported on a multiwalled carbon nanotube (MWCNT)/carbon paper (CP) electrode are powerful electrocatalysts for hydrogen production in aqueous media at pH 7. The high turnover numbers encountered (TON up to 50980) after long reaction times (up to 16 h) are explained by the increased electroactive cobalt concentration on the modified electrode, which is ca. 4 times higher than that of a state-of-the-art cobalt porphyrin electrocatalyst. These findings point out that immobilizing well-defined, multinuclear, low-cost metal complexes on carbon material is a promising strategy to design highly electroactive electrodes enabling production of green energies

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph–CC−)_2–<i>n</i>Ru­(dppe)₂(−CC-bipyM­(hfac)₂)_<i>n</i>] (<i>n</i> = 1, 2; M = Cu^II, Mn^II; bipy = 2,2′-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic Cu^II units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.3 Å between adjacent Cu and Ru centers, 16.6 Å between external Cu centers) and compared at two different redox states. Surprisingly, oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to weaker magnetic interactions. In contrast, in the simpler parent complexes bearing only one paramagnetic metal unit [Ph–CC–Ru­(dppe)₂-CC–bipyCu­(hfac)₂], one-electron oxidation of the ruthenium bis­(acetylide) unit generates an interaction between the Cu and Ru spin carriers of magnitude comparable to that observed between the two far apart Cu ions in the above corresponding neutral trimetallic system. Evaluation and rationalization of this coupling with theoretical tools are in rational agreement with experiments for such complex systems

Multicolor Photoinitiators for Radical and Cationic Polymerization: Monofunctional vs Polyfunctional Thiophene Derivatives

Thiophene and polythiophene derivatives have been prepared and used as photoinitiators upon visible light exposure. Their abilities to initiate, when combined with an iodonium salt (and optionally <i>N</i>-vinylcarbazole), a ring-opening cationic photopolymerization of epoxides and radical photopolymerization of acrylates under various different irradiation sources (i.e., very soft halogen lamp irradiation, laser diode at 405, 457, 473, 532, and 635 nm and blue LED bulb at 462 nm) have been investigated. These systems are characterized by a remarkable performance for purple to red light exposure. They are also particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and lead to the formation of an interpenetrated polymer network IPN (30 s for getting tack-free coatings). Their migration stability is excellent in the cured IPNs. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques