Ni
4
O
4
cubanes (μ
3
-
L
1
O
)NiCl(MeOH)
4
(
1
) and (μ
3
-
L
2
O
)NiCl(H
2
O)
4
(
2
) (
L
1
OH
= 1-
H
-2-benzimidazolylmethanol,
L
2
OH
= 1-methyl-2-benzimidazolylmethanol) self-assemble from ...commercially available 1-
H
- and 1-methyl-2-benzimidazolylmethanol and NiCl
2
·6H
2
O in high yields under mild conditions. Both complexes were characterised spectroscopically and by X-ray crystallography. The cubanes oxidise water electrocatalytically to dioxygen at neutral pH in aqueous potassium phosphate buffer solutions.
Ni
4
O
4
cubanes (μ
3
-
L
1
O
)NiCl(MeOH)
4
(
1
) and (μ
3
-
L
2
O
)NiCl(H
2
O)
4
(
2
) (
L
1
OH
= 1-
H
-2-benzimidazolylmethanol,
L
2
OH
= 1-methyl-2-benzimidazolylmethanol) self-assemble, providing easy access to oxygen evolution electrocatalysts.
The reaction between
p
-nitrosonitrobenzene and the tetramethylpropylenediamine-copper(
i
) complex yields a dinuclear complex that is structurally and electronically similar to side-on peroxo ...species known in Cu/O
2
chemistry. The complex reacts with di-
tert
-butylphenolate
via
nitrene transfer, as observed through an intermediate and the aminophenol product obtained upon reductive work-up.
The reaction between
p
-nitrosonitrobenzene and the tetramethylpropylenediamine-copper(
i
) complex yields a dinuclear complex that has similar topology, electronic structure and reactivity as side-on peroxo species known in Cu/O
2
chemistry.
The Cover Feature depicts the photocatalytic CO2 reduction using for the first time the iron porphyrin derivative FeIII(TF4TMAP)(CF3SO3)5 as molecular catalyst. In their Research Article, M. Orio, G. ...Charalambidis, A. G. Coutsolelos and co‐workers demonstrate that after light irradiation, CO2 to CO conversion was observed, achieving excellent turnover numbers (up to 5500 TONs) and high selectivity. More information can be found in the Research Article by M. Orio, G. Charalambidis, A. G. Coutsolelos and co‐workers.
Abstract
The photocatalytic CO
2
reduction into value‐added chemicals is regarded as one promising technology to mitigate environmental issues and the energy crisis of the modern world due to the ...extended CO
2
emissions. Recent advances have shown that iron porphyrins are considered as one of the most efficient molecular catalysts in the activation and reduction of molecules like CO
2
. Thus, a suitably modified Fe
III
porphyrin (Fe
III
(TF
4
TMAP)(CF
3
SO
3
)
5
) was prepared and its catalytic activity in terms of photocatalytic reduction of CO
2
was studied. This iron catalyst possesses four fluorine substituents in the
ortho
and the
meta
position of each
meso
‐phenyl group of the porphyrin, while trimethylammonium groups were placed in the
para
position. Photocatalytic studies were performed in the presence of an iridium complex as a chromophore and have shown that Fe
III
(TF
4
TMAP)(CF
3
SO
3
)
5
can effectively reduce CO
2
, achieving excellent turnover numbers (up to 5500 TONs) and high turnover frequencies. The main reduction product of this photocatalytic system was CO, and only a small amount of hydrogen was detected, presenting a maximum selectivity of 86 % for CO.
Twelve structural models for the S-2 state of the oxygen-evolving complex (OEC) of photosystem II are evaluated in terms of their magnetic properties. The set includes ten models based on the 'fused ...twist' core topology derived by polarized EXAFS spectra and two related models proposed in recent mechanistic investigations. Optimized geometries and spin population analyses suggest that Mn(III), which is most often identified with the manganese ion at site D, is always associated with a penta- coordinate environment, unless a chloride is directly ligated to the metal. Exchange coupling constants were determined by broken- symmetry density functional theory calculations and the complete spectrum of magnetic sublevels was obtained by direct diagonalization of the Heisenberg Hamiltonian. Seven models display a doublet ground state and are considered spectroscopic models for the ground state corresponding to the multiline signal (MLS) of the S-2 state of the OEC, whereas the remaining five models display a sextet ground state and could be related to the g = 4.1 signal of the S-2 state. It is found that the sign of the exchange coupling constant between the Mn centres at positions A and B of the cluster is directly related to the ground state multiplicity, implying that interconversion between the doublet and sextet can be induced by only small structural perturbations. The recently proposed quantum chemical method for the calculation of Mn-55 hyperfine coupling constants is subsequently applied to the S-2 MLS state models and the quantities that enter into the individual steps of the procedure (site-spin expectation values, intrinsic site isotropic hyperfine parameters and projected Mn-55 isotropic hyperfine constants) are analyzed and discussed in detail with respect to the structural and electronic features of each model. The current approach performs promisingly. It reacts sensitively to structural distortions and hence may be able to distinguish between different structural proposals. Thus it emerges as a useful contributor to the ongoing efforts that aim at establishing correlations between the body of spectroscopic data available for the various Si states of the OEC and their actual geometric features.
We report the synthesis and the characterization of a trinuclear nickel complex. Solid state and solution studies using X-ray diffraction, NMR and UV-vis spectroscopy highlight the square planar ...geometries around the metal centers and an all-sulfur coordination sphere. It exhibits significant electrocatalytic activity for hydrogen evolution in DMF using Et
3
NHCl as the proton source. DFT studies suggest that sulfur atoms act as proton relay, as proposed in NiFe hydrogenases.
A trinuclear nickel complex with
S
-based ligands is reported as a bio-inspired model of the NiFe hydrogenases' active site. DFT calculations indicate that thiolate and thioether functions are involved as proton relays in the H
2
evolution mechanism.
Understanding the structure and function of lytic polysaccharide monooxygenases (LPMOs), copper enzymes that degrade recalcitrant polysaccharides, requires the reliable atomistic interpretation of ...electron paramagnetic resonance (EPR) data on the Cu(II) active site. Among various LPMO families, the chitin-active PlAA10 shows an intriguing phenomenology with distinct EPR signals, a major rhombic and a minor axial signal. Here, we combine experimental and computational investigations to uncover the structural identity of these signals. X-band EPR spectra recorded at different pH values demonstrate pH-dependent population inversion: the major rhombic signal at pH 6.5 becomes minor at pH 8.5, where the axial signal dominates. This suggests that a protonation change is involved in the interconversion. Precise structural interpretations are pursued with quantum chemical calculations. Given that accurate calculations of Cu g-tensors remain challenging for quantum chemistry, we first address this problem via a thorough calibration study. This enables us to define a density functional that achieves accurate and reliable prediction of g-tensors, giving confidence in our evaluation of PlAA10 LPMO models. Large models were considered that include all parts of the protein matrix surrounding the Cu site, along with the characteristic second-sphere features of PlAA10. The results uniquely identify the rhombic signal with a five-coordinate Cu ion bearing two water molecules in addition to three N-donor ligands. The axial signal is attributed to a four-coordinate Cu ion where only one of the waters remains bound, as hydroxy. Alternatives that involve decoordination of the histidine brace amino group are unlikely based on energetics and spectroscopy. These results provide a reliable spectroscopy-consistent view on the plasticity of the resting state in PlAA10 LPMO as a foundation for further elucidating structure–property relationships and the formation of catalytically competent species. Our strategy is generally applicable to the study of EPR parameters of mononuclear copper-containing metalloenzymes.
Nitrogen‐doped carbon dots were used as photosensitizers for H2 evolution in the presence of a series of mononuclear thiosemicarbazone nickel complexes. The catalysts were designed to display ...different substituents at the para position of the phenyl rings. These chemical modifications tune the electron‐donating abilities of the complexes and influence their capability to reduce protons into hydrogen. All photocatalytic experiments were performed in aqueous solution, using as sacrificial electron donor TCEP/Asc (1 : 1), 0.1 M each, at pH=5. The complex bearing the most electron‐donating ligand with the dimethylamino (N(CH3)2) substituent behaves as the best catalyst in our series of photocatalytic systems with TONCAT=148, under white led radiation for 30 h. Therefore, this noble metal‐free system can effectively produce hydrogen in water and further chemical modification of the ligand will likely improve its production.
A noble metal‐free photocatalytic system was designed by combining nitrogen‐doped carbon dots as photosensitizers and a dimethylamino‐thiosemicarbazone nickel catalyst. This promising system is shown to photoinduce hydrogen production (TONCAT=148) upon irradiation in aqueous medium.
A new mixed-valent dicopper complex 5 was generated from ligand exchange by dissolving a bis(CH3CN) precursor 3 in acetone. Introduction of a water molecule in place of an acetonitrile ligand was ...evidenced by base titration and the presence of a remaining coordinated CH3CN by IR, 19F NMR, and theoretical methods. The proposed structure (CH3CN–Cu–(SR)–Cu–OH2) was successfully DFT-optimized and the calculated parameters are in agreement with the experimental data. 5 has a unique temperature-dependence EPR behavior, with a localized valence from 10 to 120 K that undergoes delocalized at room temperature. The electrochemical signatures are in the line of the other aquo parent 2 and sensibly different from the rest of the series. Similar to the case of 2, 5 was finally capable of single turnover N2O reduction at room temperature. N2 was detected by GC-MS, and the redox character was confirmed by EPR and ESI-MS. Kinetic data indicate a reaction rate order close to 1 and a rate 10 times faster compared to 2. 5 is thus the second example of that kind and highlights not only the main role of the Cu–OH2 motif, but also that the adjacent Cu-X partner (X = OTf– in 2 and CH3CN in 5) is a new actor in the casting to establish structure/activity correlations.
PDF
