4 research outputs found
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 [NiÂ(Et-thiazdt)<sub>2</sub>]<sup><i>n</i></sup>, with <i>n</i> =
â2, â1, 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
NâMe 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 [NiÂ(Et-thiazdt)<sub>2</sub>]<sup>â1</sup>, as Ph<sub>4</sub>P<sup>+</sup> salt,
exhibits side-by-side lateral interactions leading to a Heisenberg
spin chain behavior. The solid-state structure of the neutral, diamagnetic
[NiÂ(Et-thiazdt)<sub>2</sub>]<sup>0</sup> 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 [AuÂ(Et-thiazdt)<sub>2</sub>]<sup>âą</sup>. 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 [NiÂ(Et-thiazdt)<sub>2</sub>]<sup>0</sup> exhibits a semiconducting
behavior with a room-temperature conductivity Ï<sub>RT</sub> â 0.014 S cm<sup>â1</sup>
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
[(PhâCîŒCâ)<sub>2â<i>n</i></sub>RuÂ(dppe)<sub>2</sub>(âCîŒC-bipyMÂ(hfac)<sub>2</sub>)<sub><i>n</i></sub>] (<i>n</i> = 1, 2; M = Cu<sup>II</sup>, Mn<sup>II</sup>; bipy = 2,2âČ-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<sup>II</sup> 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 Ă
between adjacent Cu and Ru centers, 16.6 Ă
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 [PhâCîŒCâRuÂ(dppe)<sub>2</sub>-CîŒCâbipyCuÂ(hfac)<sub>2</sub>], one-electron
oxidation of the ruthenium bisÂ(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