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As Associations of researchers active in advocacy activities, we are deeply humbled by the courage shown by Iranian people, and especially women, since the start of protests on September 16. As Associations which advocate for human rights, we wish to express our unreserved solidarity towards the women of Iran and Afghanistan, and all oppressed women living in the world, who suffer with their connationals from privation of human rights, and are further discriminated against because of their gender. As Associations which advocate for freedom to do research for all, we extend our solidarity to all researchers working in regions where academic and scientific freedom is not recognized and guaranteed, and where research can be a life-risk job. As Associations which advocate for research ethics and integrity, we support the freedom to do research for all researchers who adopt their research methods to question the existing social, economic and political status quo, independently from their national origin, their cultural identity and ideological background. Research as a crime The ongoing protests in Iran have raised the world public opinion’s attention over violation of human rights once again. We know that violation of human rights is a daily reality for people living in many countries. Many of them are researchers. Since the Islamic Revolution, a large number of researchers have been arrested, detained and tortured by the Iranian government because of their research activity and international networks. A case which has gained international attention, especially thanks to Amnesty International, is that of Ahmad Reza Djalali. But there are many cases to be mentioned one by one here: the phrase “academic prisoners” is used to indicate them collectively. Of course, it is not an exclusive Iranian practice: in Egypt in 2016, the Italian PhD candidate Giulio Regeni was arrested, tortured and killed, while Patrick Zaki is currently facing trial, as too many of his connationals. To be women and scholars is even more dangerous, especially in political contexts as the Iranian and Afghan ones, where the Institutions are enforcing measures that restrict women’s freedom and rights as humans, before that as scholars, as made evident by the recent decision of Afghan authorities to prevent women from accessing education. A criminalization of research to various degrees can be seen in other countries as well, for example in Turkey or in Poland and academic freedom is strongly threatened in other countries like in Hungary. Research as a tool for political change The relevance of the status of women and of that of gender roles in society is strongly highlighted by the case of the conspiracy theories on a so-called “gender ideology”. This ideology spreads widely, including in Europe, where political movements call to “protect the traditional family” or the “respect of the religious faith” in order to take action against the academic system and to restrict all scientific research linked with gender studies. We believe that because research is based on freedom of thought and expression, it provides citizens with ways to analyse and criticise social, economic, and political developments. Thus, it is dangerous for authoritarian regimes and for governments that, without being fully authoritarian, push their country towards a progressive restriction of freedoms. We believe that research practice and findings can always have political implications, and thus can be equally important tools for advocacy. For this reason, academic and scientific freedom must be protected, as a founding element of democracy, from those who want to silence it and control it. It is thus crucial that Research Performing and Research Funding Organisations, as well as individual researchers, make it their priority to respect and value academic integrity, while actively guaranteeing academic freedom as a human right. At the same time, we can not advocate for academic and scientific freedom without supporting and protecting the freedom of thought and of expression as citizens: scholars are not separated from society, and we believe that their knowledge must be accepted also in the public debate as intellectuals, and not only as specialist workers restricted to their own field. Among all cases, we cite here as an example the one that involved Turkish scholar Şebnem Korur Fincancı, highlighted by the Academic Freedom Monitoring Project of Scholars at Risk. European researchers advocate for concrete support to researchers persecuted for their research activity As researchers’ associations who advocate to protect research ethics and integrity, and against any restrictions to academic freedom,we believe that the global academic community needs to be open to different approaches. As European-based Associations, we feel the need to highlight our support for the freedom of all scholars to carry out research from their chosen cultural and/or political perspective in a safe and respectful environment. This is even more important for those scholars who are based in, or come from, non- Western countries: their perspective can be novel to the majority of the European academic community, and thus they may be more exposed to epistemic violence or injustice. We all need to ensure that this does not happen.

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand σ-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal CuIII complex [Cu(CF3)4]1- , in which the metal center tries to populate its formally unoccupied 3dx2-y2 orbital via σ-bonding, leading to a reduced d10 CuI description. However, Au L3-edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the AuIII species is still possible, showing that a genuine d10 configuration is not achieved. We also find an increased electron-sharing nature of the σ-bonds in the AuI species, relative to their AgI and CuI analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5dx2-y2 or 6s orbital, respectively, in bonding, indicating why AuI and AuIII complexes often have similar reactivity.

The influence of the support-oxygen groups and Pt particle size on the catalytic performance of Pt/AC for the aerobic oxidation of α-D-glucose to gluconic acid (glycolate) was studied. Surface-oxygen groups were introduced by treating the activated carbon support with diluted HNO 3 without significantly affecting the support porosity. The platinum particle size could be decreased on both the treated and untreated support by adding an additional calcination step to the synthesis. The presence of oxygen-containing groups is shown to be highly beneficial (∼4 fold increase in the turnover frequency) only for the smallest Pt particle size (1.8–2.5 nm, determined by TEM). For the catalyst with the larger Pt size (3.4–3.6 nm), the presence of additional oxygen-contacting groups does not significantly enhance the activity. Since the size of the smaller Pt particles is close to the product/substrate molecular diameter (glucose/gluconic acid, ∼0.9 nm) the observed effect can be attributed to the effective repulsion by the negatively charged oxygen groups in close proximity to the glycolate reaction product. The increase in activity originates from the resulting enhanced desorption of glycolate by alleviating the product inhibition presence due to the strong interaction of glycolate with Pt.

Nickel-catalyzed cross-coupling reactions have become a powerful methodology to construct C-heteroatom bonds. However, many protocols suffer from competitive off-cycle reaction pathways and require non-equimolar amounts of coupling partners to suppress them. Here, we report on mechanistic examination of carboxylate O-arylation under thermal conditions, in both the presence and absence of an exogeneous bipyridine-ligand. Furthermore, spectroscopic studies of the novel ligand-free carboxylate O-arylation reaction unveiled the resting state of the nickel catalyst, the crucial role of the alkylamine base and the formation of an off-cycle NiI−NiII dimer upon reduction. This study provides insights into the competition between productive catalysis and deleterious pathways (comproportionation and protodehalogenation) in the commonly proposed self-sustained NiI/NiIII catalytic cycle. Thereby we show that for productive nickel-catalyzed carboxylate O-arylation a choice must be made between either mild conditions or equimolar ratios of substrates.

The oxidation state of the redox noninnocent tetra-amido macrocyclic ligand (TAML) scaffold was recently shown to affect the formation of nitrene radical species on cobalt(III) upon reaction with PhI=NNs [van Leest N. P.; J. Am. Chem. Soc.2020, 142, 552-563]. For the neutral

MAX phases are layered ternary carbides or nitrides that are attractive for catalysis applications due to their unusual set of properties. They show high thermal stability like ceramics, but they are also tough, ductile, and good conductors of heat and electricity like metals. Here, we study the potential of the Ti3AlC2 MAX phase as a support for molybdenum oxide for the reverse water–gas shift (RWGS) reaction, comparing this new catalyst to more traditional materials. The catalyst showed higher turnover frequency values than MoO3/TiO2 and MoO3/Al2O3 catalysts, due to the outstanding electronic properties of the Ti3AlC2 support. We observed a charge transfer effect from the electronically rich Ti3AlC2 MAX phase to the catalyst surface, which in turn enhances the reducibility of MoO3 species during reaction. The redox properties of the MoO3/Ti3AlC2 catalyst improve its RWGS intrinsic activity compared to TiO2- and Al2O3-based catalysts. We thank the Netherlands Organisation for Scientific Research (NWO) for the grant “Developing novel catalytic materials for converting CO2, methane and ethane to high-value chemicals in a hybrid plasma-catalytic reactor” (China.15.119). We also acknowledge financial support by MINECO (Spain) through projects MAT2017-86992-R and MAT2016-80285-P. Z.S. was supported by the project LTAUSA19034, from the Ministry of Education Youth and Sports (MEYS). M.H. and M.T. gratefully acknowledge NWO under LIFT, Launchpad for Innovative Future Technology, PreCiOuS, 731.015.407. We also thank the staff of the Swiss Light Source (SLS) synchrotron (SuperXAS beamline and proposal number 20190956), Maarten Nachtegaal and Adam Clark, for support during synchrotron measurements.

Copper aluminate spinel (CuO.CuAl2O4) is the favoured Cr-free substitute for the copper chromite catalyst (CuO.CuCr2O4) in the industrial hydrogenation of aldehydes. New insights in the catalytic mechanism were obtained by systematically studying the structure and activity of these catalysts including effects of manganese as a catalyst component. The hydrogenation of butyraldehyde to butanol was studied as a model reaction and the active structure was characterised using X-ray diffraction, temperature programmed reduction, N2O chemisorption, EXAFS and XANES, including in-situ investigations. The active catalyst is a reduced spinel lattice that is stabilised by protons, with copper metal nanoparticles grown upon its surface. Incorporation of Mn into the spinel lattice has a profound effect on the spinel structure. Mn stabilises the spinel towards reduction of CuII to Cu0 by occupation of tetrahedral sites with Mn cations, but also causes decreased catalytic activity. Structural data, combined with the effect on catalysis, indicate a predominantly interface-based reaction mechanism, involving both the spinel and copper nanoparticle surface in protonation and reduction of the aldehyde. The electron reservoir of the metallic copper particles is regenerated by the dissociative adsorption and oxidation of H2 on the metal surface. The generated protons are stored in the spinel phase, acting as proton reservoir. Cu(I) species located within the spinel and identified by XANES are probably not involved in the catalytic cycle.

Kinetic analysis of polyesterification reactions using Lewis-acidic metal catalysts have been performed. While Sn-based catalysts are superior to Ti-based catalysts under neat polycondensation conditions (high [H2O]), the result is inverted under azeotropic conditions (low [H2O]). These findings show that the catalytic activity is crucially determined by the robustness of the catalyst against hydrolytic degradation.

Nickel-catalyzed cross-coupling reactions have become a powerful methodology to construct C–heteroatom bonds. How-ever, many protocols suffer from competitive off-cycle reaction pathways and require non-equimolar amounts of cou-pling partners to suppress them. Here, we report on mechanistic examination of carboxylate O-arylation under thermal conditions, in both the presence and absence of an exogeneous bipyridine-ligand. Furthermore, spectroscopic studies of the novel ligand-free carboxylate O-arylation reaction unveiled the resting state of the nickel catalyst, the crucial role of the alkylamine base and the formation of a catalytically relevant NiI–NiII dimer upon reduction. This study provides in-sights into the competition between productive catalysis and deleterious pathways (comproportionation and pro-todehalogenation) that exist for all elementary steps in the commonly proposed self-sustained NiI/NiIII catalytic cycle. Thereby we show that for productive nickel-catalyzed carboxylate O-arylation a choice must be made between either mild conditions or equimolar ratios of substrates.

Esterification is a key reaction and is used in many synthetic and industrial processes, yet the detailed mechanism of operation of often-used (Lewis acid) catalysts is unknown and subject of little research. Here, we report on mechanistic studies of a titanium aminotriphenolate catalyst, using stoichiometric and catalytic reactions combined with kinetic data and density functional theory (DFT) calculations. While often only the Lewis acidity of the Ti-center is taken into account, we found that the amphoteric nature of this catalyst, combining this Lewis acidity with Brønsted basicity of a Ti-bound and in situ formed carboxylate group, is crucial for catalytic activity. Furthermore, hydrogen bonding interactions are essential to pre-organize substrates and to stabilize various intermediates and transition states and thus enhancing the overall catalytic reaction. These findings are not only applicable to this class of catalysts, but could be important for many other esterification catalysts.

Cr-catalyzed ethene trimerization is an industrially important process to produce 1-hexene. Despite its industrial relevance, the changing oxidation state and the structural rearrangements of the metal center during the catalytic cycle remain unclear. In this study, we have investigated the active species in a [(R-SN(H)S-R)CrCl3] (R=C10H21) catalyzed ethene trimerization system using a combination of spectroscopic techniques (XAS, EPR and UV/VIS) and DFT calculations. Reaction of the octahedral CrIII complex with modified methylaluminoxane (MMAO) in absence of ethene gives rise to the formation of a square-planar CrII complex. In the presence of ethene (1 bar), no coordination was observed, which we attribute to the endergonic nature of the coordination of the first ethene molecule. Employing an alkyne as a model for ethene coordination leads to the formation of a dinuclear cationic CrIII alkyne complex. DFT calculations show that a structurally related dinuclear cationic CrIII ethene complex could form under catalytic conditions. Comparing a mechanism proceeding via mononuclear cationic CrII/CrIV intermediates to that proceeding via dinuclear cationic CrII/CrIII intermediates demonstrates that only the mechanism involving mononuclear cationic CrII/CrIV intermediates can correctly explain the observed product selectivity.

The redox noninnocence of the TAML scaffold in cobalt-TAML (tetra-amido macrocyclic ligand) complexes has been under debate since 2006. In this work, we demonstrate with a variety of spectroscopic measurements that the TAML backbone in the anionic complex [CoIII(TAMLred)](-) is truly redox noninnocent and that one-electron oxidation affords [CoIII(TAMLsq)]. Multireference (CASSCF) calculations show that the electronic structure of [CoIIITAMLsq)] is best described as an intermediate spin (S = 1) cobalt(III) center that is antiferromagnetically coupled to a ligand-centered radical, affording an overall doublet (S = 1/2) ground-state. Reaction of the cobalt(III)-TAML complexes with PhINNs as a nitrene precursor leads to TAML-centered oxidation and produces nitrene radical complexes without oxidation of the metal ion. The ligand redox state (TAML(red) or TAMLsq) determines whether mono- or bis-nitrene radical complexes are formed. Reaction of [CoIII(TAMLsq)] or [CoIII(TAMLred)](-) with PhINNs results in the formation of [CoIII(TAMLq)(N(center dot)Ns)] and [CoIII(TAMLq)(N·Ns)2]-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron-reduced Fischer-type nitrene radicals (N(center dot)Ns(-)) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV-vis spectroscopy, high-resolution mass spectrometry, magnetic moment measurements, and supporting CASSCF calculations.

Di-iron dithiolate hydrogenase model complexes are promising systems for electrocatalytic production of dihydrogen and have therefore been spectroscopically and theoretically investigated in this study. The direct effect of ligand substitution on the redox activity of the complex is examined. In order to understand and eventually optimize such systems, we characterised both metal and ligand in detail, using element specific X-ray absorption Fe- and S-K edge XAS. The (electronic) structure of three different [Fe2S2] hydrogenase systems in their non-reduced state was investigated. The effect of one- and two-electron reduction on the (electronic) structure was subsequently investigated. The S K-edge XAS spectra proved to be sensitive to delocalization of the electron density into the aromatic ring. The earlier postulated charge and spin localization in these complexes could now be measured directly using XANES. Moreover, the electron density (from S K-edge XANES) could be directly correlated to the Fe-CO bond length (from Fe K-edge EXAFS), which are in turn both related to the reported catalytic activity of these complexes. The delocalization of the electron density into the conjugated π-system of the aromatic moieties lowers the basicity of the diiron core and since protonation occurs at the diiron (as a rate determining step), lowering the basicity decreases the extent of protonation and consequently the catalytic activity.

The purpose of this study was to evaluate the impact of virtual reality on undergraduate students’ self-efficacy, self-concept, interest, and laboratory anxiety in an introductory chemistry course. We used a mixed-methods approach to improve our understanding of how these factors mediate student learning. The findings showed that (i) the use of the virtual reality application had an overall positive impact on students’ self-efficacy, self-concept, interest, and anxiety; and (ii) students who expressed some anxiety about doing the lab prior to the course reported the use of the virtual reality application decreased their levels of anxiety at the end of the lab. The implications of these findings speak to the potential value of the use of virtual reality applications in higher education and especially in situations when distance learning is the only option as well as in situations where the costs of real laboratories cannot be afforded. ispartof: Eurasia Journal Of Mathematics Science And Technology Education vol:18 issue:3 status: published

One of the greatest challenges of our time is to mitigate the global climate change caused by anthropogenic emission of greenhouse gases, mainly generated by use of fossil fuels. A critical part of the solution is to substitute energy generation based on fossil fuels by the more renewable energy sources (solar, wind, geothermal power and others) and one of the main issues is to provide efficient energy storage for a large subset of intermittent energy sources. This can be achieved by various means, such as physical storage (e.g. pump hydro storage, flywheels, compressed air) and/or chemical conversion (e.g. batteries, hydrogen and ammonia generation and storage, artificial carbon-based fuels) (Figure 1). The second family of the energy storage solutions is close to maturity for commercial deployment, therefore research and development proceeds at a fast pace and enjoys significant investments at all levels. For this reason, it is foreseen that the activities in this direction will be an important role for CERIC-ERIC in the near future. While the involvement of CERIC-ERIC in the research on electrochemical batteries has been already discussed a the previous report (Bozzini 2020), the present document on the one hand focuses on the assessment of CERIC-ERIC activities in the field of electrochemical energy conversion by various types of fuel cells and, on the other hand, expounds recommendations to enhance its the role of this fuel cell community.

In [Fe-Fe] hydrogenase mimic systems the ene-1,2-dithiolene ligands play an important role in the stabilisation of the redox-active metal center. This is demonstrated by the benzenedithiolene (bdt) analogue, featuring six terminal carbonyl ligands connected to a di-iron metal center, i.e. [Fe2(bdt)(CO)6]. Here we present a combined experimental and theoretical study that elucidates key intermediates [Fe2(bdt)(CO)6]1- and [Fe2(bdt)(μ-CO)(CO)5]2- in the electrocatalytic production of dihydrogen. A DFT study shows that [Fe2(bdt)(CO)6]1- is the kinetic product after the first one electron reduction, while the previously proposed bridging intermediate species [Fe2(bdt)(μ-CO)(CO)5]1- is kinetically inaccessible. The doubly reduced species [Fe2(bdt)(μ-CO)(CO)5]2- was for the first time structurally characterized using EXAFS. XANES analysis confirms the existence of reduced iron zero species and confirms the distorted geometry that was suggested by the DFT calculations. Combining IR, UV-vis and XAS spectroscopic results with TD-DFT and FEFF calculations enabled us to assign the key-intermediate [Fe2(bdt)(CO)6]2-. This study emphasizes the strengths of combining computational chemistry with advanced spectroscopy techniques.

Two novel κ2‐C,N‐pyridine bridged [FeFe]‐H2ase mimics (1 and 2) have been prepared and are shown to function as efficient molecular catalysts for electrocatalytic proton reduction. The elemental and structural composition of the complexes are confirmed by NMR and IR spectroscopy, high‐resolution mass spectrometry and single‐crystal X‐ray diffraction. Electrochemical investigations reveal that the complexes reduce protons at their first reduction potential, resulting in the lowest overpotential (120 mV) ever reported for [FeFe]‐H2ase mimics in proton reduction catalysis when mild acid (phenol) is used as proton source.

Transition metal dissolution from the cathode active material and its deposition on the anode causes significant cell aging, studied most intensively for manganese. Owing to their higher specific energy, the current focus is shifting towards nickel-rich layered LiNixMnyCozO2 (NMC, x + y + z = 1) with x > 0.5, so that the effect of Ni dissolution on cell degradation needs to be understood. This study investigates the dissolution of transition metals from a NMC622 cathode and their subsequent deposition on a graphite anode using operando X-ray absorption spectroscopy. We show that in NMC622-graphite cells transition metals dissolve nearly stoichiometrically at potentials > 4.6 V, highlighting the significance of investigating Ni dissolution/deposition. Using NMC622-graphite full-cells with electrolyte containing the bis(trifluoromethane) sulfonimide (TFSI) salts of either Ni, Mn, or Co, we compare the detrimental impact of these metals on cell performance. Using in-situ and ex-situ XRD, we show that the aging mechanism induced by all three metals is the loss of cycleable lithium in the solid electrolyte interface (SEI) of the graphite. This loss is larger in magnitude when Mn is present in the electrolyte compared to Ni and Co, which we ascribe to a higher activity of deposited Mn towards SEI decomposition in comparison to Ni and Co. (C) The Author(s) 2019. Published by ECS.

1-Hexene is an important α-olefin for polyethylene production and is produced from ethene. Recent developments in the α-olefin industry have led to the successful commercialization of ethene trimerization catalysts. An important industrially applied ethene trimerization system uses a mixture of chromium 2-ethylhexanoate, AlEt3, AlEt2Cl, and 2,5-dimethylpyrrole (DMP). Here, we have studied the activation of this system using catalytic and spectroscopic experiments (XAS, EPR, and UV–vis) under conditions employed in industry. First, chromium 2-ethylhexanoate was prepared and characterized to be [Cr3O(RCO2)6(H2O)3]Cl. Next, the activation of chromium 2-ethylhexanoate with AlEt3, AlEt2Cl, and DMP was studied, showing immediate reduction (

Monoalkyltin(iv) complexes are well-known catalysts for esterification reactions and polyester formation, yet the mode of operation of these Lewis acidic complexes is still unknown. Here, we report on mechanistic studies of n-butylstannoic acid in stoichiometric and catalytic reactions, analyzed by NMR, IR and MS techniques. While the chemistry of n-butyltin(iv) carboxylates is dominated by formation of multinuclear tin assemblies, we found that under catalytically relevant conditions only monomeric n-BuSn(OAc)3 and dimeric (n-BuSnOAc2OEt)2 are present. Density functional theory (DFT) calculations provide support for a mononuclear mechanism, where n-BuSn(OAc)3 and dimeric (n-BuSnOAc2OEt)2 are regarded as off-cycle species, and suggest that carbon–oxygen bond breaking is the rate-determining step., Monoalkyltin-catalyzed esterification was studied under industrially relevant catalytic conditions and was found to have a monomeric active species, with both a monomeric and a dimeric resting state.

In recent years there have been regular reports about a new generation of batteries in which the liquid electrolyte is replaced by a solid material: the solid-state batteries. With a higher energy density and a better safety than current batteries, solid-state batteries potentially would boost electric mobility by enhancing the driving distance of e-cars and prevent extreme battery fires. Why are they not yet implemented in the latest generation of e-cars?

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ

The reaction of the ethene tetramerization catalyst, ((C6H5)2P)2NiPrCrCl3(THF) (complex 1), and ethene trimerization catalyst, ((o-C6H4OMe)2P)2NMeCrCl3 (complex 2), with alkylaluminum reagents (AlMe3 and MMAO) was investigated using spectroscopic techniques (Cr K-edge XAS, X-band EPR and UV-vis) and catalytic studies. In all cases the majority of chromium was reduced to the divalent oxidation state and only a minor fraction of chromium was reduced further to the monovalent oxidation state. It is demonstrated that MMAO and the ligand (through a pendant ether donor) can facilitate ion pair formation for these divalent Cr complexes, providing insights into the role of the ligand and activator in the activation process. Via the use of dienes, we succeeded in characterizing a monocationic CrII alkene complex, providing evidence that catalysis could proceed via cationic CrII/CrIV intermediates. This is supported by DFT calculations, where it is shown that a mechanism proceeding via dicationic CrII/CrIV intermediates explains the observed product selectivity.

X-ray spectroscopy is an important tool for scientific analysis. While the earliest demonstration experiments were realised in the laboratory, with the advent of synchrotron light sources most of the experiments shifted to large scale synchrotron facilities. In the recent past there is an increased interest to perform X-ray experiments also with in-house laboratory sources, to simplify access to X-ray absorption and X-ray emission spectroscopy, in particular for routine measurements. Here we summarise the recent developments and comment on the most representative example experiments in the field of in-house laboratory X-ray spectroscopy. We first give an introduction and some historic background on X-ray spectroscopy. This is followed by an overview of the detection techniques used for X-ray absorption and X-ray emission measurements. A short paragraph also puts related high energy resolution and resonant techniques into context, though they are not yet feasible in the laboratory. At the end of this section the opportunities using wavelength dispersive X-ray spectroscopy in the laboratory are discussed. Then we summarise the relevant details of the recent experimental laboratory setups split into two separate sections, one for the recent von Hamos setups, and one for the recent Johann/Johansson type setups. Following that, focussing on chemistry and catalysis, we then summarise some of the notable X-ray absorption and X-ray emission experiments and the results accomplished with in-house setups. In a third part we then discuss some applications of laboratory X-ray spectroscopy with a particular focus on chemistry and catalysis., Coordination Chemistry Reviews, 423, ISSN:0010-8545

The triplet excited state of a new Ir-based photosensitizer with two chromenopyridinone and one bipyridine-based ligands has been studied by pump-probe X-ray absorption near edge structure (XANES) spectroscopy coupled with DFT calculations. The excited state has a lifetime of 0.5 μs in acetonitrile and is characterized by very small changes of the local atomic structure with an average metal-ligand bond length change of less than 0.01 Å. DFT-based calculations allow the interpretation of the XANES in the energy range of ∼50 eV around the absorption edge. The observed transient XANES signal arises from an additional metal-centered Ir 5d vacancy in the excited state which appears as a result of electron transfer from the metal to the ligand. The overall energy shift of the excited state spectrum originates from the shift of 2p and unoccupied states induced by screening effects. The approach for the analysis of time-resolved spectra of 5d metal complexes is quite general and can also be used if excited and ground state structures are significantly different.

Selective copper(I) to palladium(0) transmetallation of P-donors from the rigid N,N'-diphosphanyl-imidazol-2-ylidene C3 H2 [NP(tBu)2 ]2 (PCNHC P) was observed when known [Cu3 (μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)3 was reacted with [Pd(PPh3 )4 ]. When 1.2 equivalents of [Pd(PPh3 )4 ] was used, the product [Cu2 Pd(μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (2(OTf)2 ) was obtained, which features a CuI -CuI -Pd0 chain and appears to be the first linear heterotrinuclear complex with d10 -d10 interactions between Pd0 and CuI . When the Cu3 precursor was reacted with 3.0 equivalents of [Pd(PPh3 )4 ], the complex [CuPd2 (μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (3(OTf)2 ) was obtained, which, on the basis of magnetic measurements, DFT calculations, and computed nuclear shieldings, was formulated as containing a Pd0 -CuI -Pd0 chain with an electron hole delocalized over the whole cation, including the metal chain. Similarly, selective transmetallation of the P-donors in [Ag3 (μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)3 from silver to palladium (originating from [Pd(PPh3 )4 ]) gave the linear chain [Ag2 Pd(μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (5(OTf)2 ), which on the basis of NMR spectroscopy comprises an AgI -AgI -Pd0 metal core. However, X-ray diffraction data collected on various samples of 5(OTf)2 were modeled with 50:50 metal disorder at the terminal positions, corresponding to a (AgI /Pd0 )-AgI -(AgI /Pd0 ) formulation. Upon standing in solution, 5(OTf)2 transformed to 6(OTf)2 , the regioisomer of 5(OTf)2 in which the Pd center has migrated to the central position of an AgI -Pd0 -AgI chain. Prolonged standing in CH2 Cl2 or by reaction with [PtCl2 (NCMe)2 ] converts complex 6(OTf)2 to the AgI /PdII complex [Ag2 PdCl2 (μ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (7(OTf)2 ). The structural data of 2(OTf)2 , 3(OTf)2 , and 7(OTf)2 establish significant heterometallophilic interactions.

The lithium–sulfur (Li–S) battery chemistry has attracted great interest in the last decade because of its outstanding theoretical gravimetric energy density compared to the state-of-the-art lithium-ion battery technology. However, practically achieved energy density is still far below the theoretical value, even in small laboratory-scale batteries. The problems seen in laboratory-scale batteries will inevitably increase during scale-up to large application-format cells, as the electrolyte to active material (AM) ratio will need to be reduced in these cells to achieve high gravimetric energy density on cell-level basis. Our study shows the unique possibility of X-ray fluorescence (XRF) mapping to visualize the spatial distribution of the AM inside operating Li–S batteries in all cell components [working electrode (WE), separator, and counter electrode (CE)]. Through a combination of operando XRF mapping and X-ray absorption spectroscopy, we show that unless self-discharge is efficiently prevented, the AM can completely dissolve and distribute throughout the cell stack within a time frame of 2 h, causing poor capacity retention. Using a polysulfide diffusion barrier between the WE and the CE, we successfully suppress these processes and thereby establish a tool for examining the sealed cathode electrode compartment, enabling sophisticated studies for future optimization of the WE processes.

The underlying mechanism of lithium-sulfur batteries is still not fully established because it involves a series of both chemical and electrochemical reactions as well as the formation of soluble polysulfide intermediates. To improve the mechanistic understanding of lithium-sulfur batteries, this study investigates chemical reactions between the Li2S cathode and more oxidized sulfur species, such as S8 and polysulfides, during the electrochemical charge of the battery. By combining the electrochemistry with X-ray absorption spectroscopy, we show that chemical reactions and, in particular, the resulting accumulation of solution species in the electrolyte are essential to oxidize Li2S at a low overpotential. Additionally, by efficiently separating the anode and cathode compartments of a battery with a lithium ion-exchanged Nafion interlayer, we establish the adverse effect of the anode on the buildup of solution intermediates. In the absence of the interlayer, polysulfide intermediates can diffuse through the separator and react at the anode's surface, while the addition of the interlayer allows the intermediates to accumulate in the separator of the cathode compartment and facilitate the oxidation of Li2S.

A reactive high-valent dinuclear nickel(IV) oxido bridged complex is reported that can be formed at room temperature by reaction of [(L) 2 Ni(II) 2 (μ-X) 3 ]X (X = Cl or Br) with NaOCl in methanol or acetonitrile (where L = 1,4,7-trimethyl-1,4,7-triazacyclononane). The unusual Ni(IV) oxido species is stabilized within a dinuclear tris-μ-oxido-bridged structure as [(L) 2 Ni(IV) 2 (μ-O) 3 ] 2+ . Its structure and its reactivity with organic substrates are demonstrated through a combination of UV-vis absorption, resonance Raman, 1 H NMR, EPR, and X-ray absorption (near-edge) spectroscopy, ESI mass spectrometry, and DFT methods. The identification of a Ni(IV)-O species opens opportunities to control the reactivity of NaOCl for selective oxidations The Ubbo Emmius fund of the University of Groningen, the European Research Council (StG, no. 279549, W.R.B.), NWO for a VIDI grant (723.014.010, D.J.M. and M.T.), The Netherlands Ministry of Education, Culture and Science (Gravity program 024.001.035, W.R.B.), MINECO (CTQ2014-59212-P and CTQ2015-70851-ERC, M.S.), Gen- Cat (2014SGR1202, M.S.), FEDER (UNGI10-4E-801, M.S.), and COST action CM1305 “ECOSTBio” (W.R.B., COSTSTSM- CM1305-29045) are acknowledged for financial support

The linear, two-coordinate and isostructural heteroleptic [M(IPr){N(SiMe3)2}] (IPr = 1,3-bis(diisopropylphenyl)-imidazol-2-ylidene), formally MI complexes (M = Co, 3; Fe, 4) were obtained by the reduction of [M(IPr)Cl{N(SiMe3)2}] with KC8, or [Co(IPr){N(SiMe3)2}2] with mes*PH2, mes* = 2,4,6-tBu3C6H2. The magnetism of 3 and 4 implies CoII and FeII centres coupled to one ligand-delocalized electron, in line with XPS and XANES data; the ac susceptibility of 4 detected a pronounced frequency dependence due to slow magnetization relaxation. Reduction of [Fe(IPr)Cl{N(SiMe3)2}] with excess KC8 in toluene gave the heteronuclear ‘inverse-sandwich’ Fe–K complex 7, featuring η6-toluene sandwiched between one Fe0 and one K+ centre.

The redox non-innocence of the TAML scaffold in cobalt-TAML (Tetra-Amido Macrocyclic Ligand) complexes has been under debate since 2006. In this work we demonstrate with a variety of spectroscopic measurements that the TAML backbone in the anionic complex [CoIII(TAMLred)]- is truly redox non-innocent, and that one-electron oxidation affords [CoIII(TAMLsq)]. Multi-reference (CASSCF) calculations show that the electronic structure of [CoIII(TAMLsq)] is best described as an intermediate spin (S = 1) cobalt(III) center that is antiferromagnetically coupled to a ligand-centered radical, affording an overall doublet (S = ½) ground-state. Reaction of the cobalt(III)-TAML complexes with PhINNs as a nitrene precursor leads to TAML-centered oxidation, and produces nitrene radical complexes without oxidation of the metal ion. The ligand redox state (TAMLred or TAMLsq) determines whether mono- or bis-nitrene radical complexes are formed. Reaction of [CoIII(TAMLsq)] or [CoIII(TAMLred)]- with PhINNs results in formation of [CoIII(TAMLq)(N•Ns)] and [CoIII(TAMLq)(N•Ns)2]-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron reduced Fischer-type nitrene radicals (N•Ns-) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV-Vis spectroscopy, high resolution mass spectrometry, magnetic moment measurements and supporting CASSCF calculations.

Two novel κ2‐C,N‐pyridine bridged [FeFe]‐H2ase mimics (1 and 2) have been prepared and are shown to function as efficient molecular catalysts for electrocatalytic proton reduction. The elemental and structural composition of the complexes are confirmed by NMR and IR spectroscopy, high‐resolution mass spectrometry and single‐crystal X‐ray diffraction. Electrochemical investigations reveal that the complexes reduce protons at their first reduction potential, resulting in the lowest overpotential (120 mV) ever reported for [FeFe]‐H2ase mimics in proton reduction catalysis when mild acid (phenol) is used as proton source.

Palladium is among the most active catalysts for the hydrogen oxidation reaction (HOR) and is thus a potential candidate for replacing platinum in fuel cell catalysis. At the same time, it is well-known to absorb large amounts of hydrogen, forming a bulk hydride phase. In several electrochemical studies conducted in liquid electrolytes and temperatures between 60 and 20 °C, the hydrogen from the hydride phase was observed to desorb at potentials positive of ∼32 to 50 mV vs the reversible hydrogen electrode (RHE). Here, we present operando spectroscopic studies in a fuel cell configuration. We first validate our experimental setup by comparing the potential dependence of hydrogen absorption into a Pd/C catalyst under nitrogen determined both by electrochemical means and by operando X-ray absorption spectroscopy (XAS) at various temperatures between 20 and 100 °C. Subsequently, we investigate the structure of the Pd/C catalyst during the HOR in a fuel cell operating at 80 °C in a H2-pump configuration. Our ...

The activation of the ethene tetramerisation catalyst system based upon [CrCl3(THF)(3)] and N(Pr-i)(PPh2)(2) has been investigated in situ via the reaction of [CrCl3{PPh2N(R)PPh2}(THF)] 1a (R = Pr-i) with excess AlMe3 in toluene. The Cr K-edge XAFS spectrum of the solution freeze quenched after 1 min reaction time indicated monomethylation of the metal with the resultant product being [CrClMe(ClAlCl3){PPh2N(R)PPh2}(THF)] 4a (R = Pr-i). After 5 minutes reaction time the XAFS spectra indicate that similar to 50% of 4a had been converted to a Cr(II) species, with the central core being high spin [CrCl2{PPh2N(R)PPh2}] 7a (R = Pr-i); a similar species, [CrClMe{PPh2N(R)PPh2}] 9a (R = Pr-i) was observed as its adduct with AlMe3 (10a) (R = Pr-i) when spectra were recorded on samples maintained at room temperature. Detailed analysis (EXAFS and XANES) indicated that 7a and 9a are stabilised by adduct formation of a Cr-Cl bond to the Lewis acids B(C6F5)(3) and AlMe3, respectively. Modelling with DFT methods indicated that five-coordination was achieved, respectively by Cr-F (11a) and Cr-C (10a) interactions. In the presence of [Ph3C][Al{OC(Bu-t(F))(3)}(4)], the Cr XAFS of the room temperature solution was inconsistent with the maintenance of a phosphine complex, but could be modelled with a site like [Cr2Me8](4-){Cr-Cr 2.01(2), Cr-C 2.14(4)}, thus demonstrating considerable variation in the effects of differing Lewis acids.

Replacement of conventional cars with battery electric vehicles (BEVs) offers an opportunity to significantly reduce future carbon dioxide emissions. One possible way to facilitate widespread acceptance of BEVs is to replace the lithium-ion batteries used in existing BEVs with a lithium-sulfur battery, which operates using a cheap and abundant raw material with a high specific energy density. These significant theoretical advantages of lithium-sulfur batteries over the lithium-ion technology have generated a lot of interest in the system, but the development of practical prototypes, which could be successfully incorporated into BEVs, remains slow. To accelerate the development of improved lithium-sulfur batteries, our work focuses on the mechanistic understanding of the processes occurring inside the battery. In particular, we study the mechanism of the charging process and obtain spatially resolved information about both solution and solid phase intermediates in two locations of an operating Li2S-Li battery: the cathode and the separator. These measurements were made possible through the combination of a spectro-electrochemical cell developed in our laboratory and synchrotron based operando X-ray absorption spectroscopy measurements. Using the generated data, we identify a charging mechanism in a standard DOL-DME based electrolyte, which is consistent with both the first and subsequent charging processes.

In Li-ion batteries the dissolution of transition metals from the cathode and their subsequent deposition on the anode are known to contribute to capacity fading. In this study, we investigate these processes using an NMC cathode and a graphite anode under operating conditions using X-ray absorption spectroscopy. The experiments are carried out in an operando cell, which allows both the time/voltage and spatially resolved determination of metal concentration and oxidation state of transition metal deposits on the graphite electrode. NMC shows a strong increase of the metal dissolution rate, if the upper cut off potential exceeds 4.6 V. Under operating conditions, the oxidation state of manganese, cobalt and nickel are found to be always +2 both on lithiated and delithiated graphite. In contrast, manganese is found to be present in the metallic state on lithiated graphite in the ex situ analysis, thus highlighting the importance of the operando characterization.

Selective copper(I) to palladium(0) transmetallation of P-donors from the rigid N,N'-diphosphanyl-imidazol-2-ylidene C

This work reveals and quantifies the inherent intracluster heterogeneity in the atomic structure and charge distribution present in supported metal catalysts. The results demonstrate that these distributions are pronounced and strongly coupled to both structural and dynamic perturbations. They also serve to clarify the nature of the dynamic bonding of nanoscale catalytic metal clusters with their supports, and the mediation of these properties due to the presence of adsorbates. These findings are supported by theoretical modeling and experimental data measured for an exemplary supported metal catalyst, Pt supported on silica, using in situ high energy resolution X-ray absorption and emission spectroscopies; in situ diffuse reflectance infrared Fourier transform spectroscopy; and ex situ scanning transmission electron microscopy.

The effect of ceria doping by oxide surface modification and controlled metal surface modification (CSM) on the structure-function properties of Rh/γ-Al2O3 catalysts in the process of CO oxidation were studied by a combined array of Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)/Energy Dispersive X-ray Absorption Fine Structure/Mass Spectrometry techniques applied simultaneously under time-resolved, in situ conditions in the temperature range of 298–573 K. The addition of each promoter element by CSM exhibits multiple effects on the catalysts structure. The DRIFTS/XAS studies indicate that CeOx facilitate the protection of Rh particles against extensive oxidation in atmospheres of air, O2 and CO, without reducing the coverage of oxidisable adsorbed CO.

Transamination of [Co{N(SiMe3)2}2]2 with C6H4(NHSiiPr3)2 gave the centrosymmetric trinuclear [{CoterN(SiMe3)2(μ-η-[o-C6H4(κNSiiPr3)2])}2Coint] (1) (Coter, Coint=terminal, internal Co, respectively), with 3-coordinate Coter, and Coint “sandwiched” between the o-phenylenes of the two ligands; experimental and computational data support CoII centres and ditopic o-amido-imino-cyclohexen-allyl ligands; magnetic studies reveal intermetallic ferromagnetic interactions and single-molecule magnet (SMM) character. One-electron reduction of 1 yielded the salt [K(18-crown-6)(THF)2][{CoterN(SiMe3)2(μ-η-[o-C6H4(κNSiiPr3)2])}2Coint] (4) with the anion isostructural to 1. The centrosymmetric Fe complex [{FeterN(SiMe3)2(μ-η-[o-C6H4(κNSiiPr3)2])}2Feint] (5), analogous to 1, was also obtained.

Homogeneous chromium catalysts for the selective conversion of ethene to hex-1-ene are formed from Cr(III) reagents, aminothioether ligands of the type HN(CH2CH2SR)2, and aluminum reagents. In this study, the early activation steps are investigated by EPR, UV–visible, and Cr K-edge XAFS spectroscopy; rapid stopped-flow mixing and a freeze-quench allows good quality EXAFS analysis of a species formed in ∼1 s of reaction. This is shown to involve reduction to Cr(II) and deprotonation of a NH group of the auxiliary ligand. This 4-coordinate metal center may act as precursor for the coordination of ethene and subsequent selective oligomerization.

Determination of the factors that affect the d-band center of catalysts is required to explain their catalytic properties. Resonant inelastic X-ray scattering (RIXS) enables direct imaging of electronic transitions in the d-band of Pt catalysts in real time and in realistic environmental conditions. Through a combination of in situ, temperature-resolved RIXS measurements and theoretical simulations we isolated and quantified the effects of bond-length disorder and adsorbate coverage (CO and H2) on the d-band center of 1.25 nm size Pt catalysts supported on carbon. We found that the decrease in adsorbate coverage at elevated temperatures is responsible for the d band shifts towards higher energies relative to the Fermi level, whereas the effect of the increase in bond-length disorder on the d-band center is negligible. Although these results were obtained for a specific case of non-interacting support and weak temperature dependence of the metal-metal bond length in a model catalyst, this work can be extended to a broad range of real catalysts.

The electronic and atomic structural properties of nanoscale metal catalysts exhibit complex influences with origins related to particle size, metal–support, and metal–adsorbate interactions. The experimental investigations of these factors, as well as the elucidation of the impacts they have on mechanisms in catalysis, are hindered by their interdependency in working catalysts. We demonstrate in this work that the features underpinning bond strains and adsorbate-bonding effects in nanometer-scale Pt catalysts supported on both γ-alumina and carbon can be distinguished and analyzed using combined high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy methods, namely, HERFD XANES and HERFD EXAFS. The work extends insights into the fluxional structural dynamics obtained in these systems, a feature harboring significant consequences for understandings of both their properties and mechanisms of action.

Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2](+) (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)2](+) (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn-Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu-N distance of 0.03 Å.

Scandium trichloride complexes with tridentate N(3)- and S(2)N-donor ligands (L(3)) have been synthesised and characterised by IR, (1)H, (13)C{(1)H} and (45)Sc NMR spectroscopy, microanalysis, and solid state and solution XAFS spectroscopy. Catalytic testing of a subset of these complexes with ethene has been undertaken in chlorobenzene with MMAO-3A and PMAO-IP at 60 °C and 40 bar ethene, giving low activity ethene polymerisation. The reactions of these complexes with MeLi and AlMe(3) were studied by (1)H, (13)C{(1)H}, (27)Al and (45)Sc NMR spectroscopy and in situ via Sc K-edge XAFS spectroscopy. Three or four mol. equivalents of MeLi react with [ScCl(3)(Me(3)-tacn)] in THF solution to form [ScMe(3)(Me(3)-tacn)] cleanly, while complexes of type [ScCl(3)(R-SNS)] {R-SNS = HN(CH(2)CH(2)SC(10)H(21))(2)} form two different species proposed to be [ScMe(3)(R-SN(Li)S)] and [ScMe(2)(R-SN(-)S)]. In contrast, in situ(45)Sc NMR and Sc K-edge XAFS spectroscopic studies of the reaction of [ScCl(3)(Me(3)-tacn)] with 10 mol. equivalents of AlMe(3) strongly suggest that alkylation at the Sc(III) centre does not occur, instead retaining the Cl(3)N(3) coordination environment and most likely forming Sc-Cl-AlMe(3) bridging interactions. Similar studies on [ScCl(3)(decyl-SNS)] with 10 mol. equivalents of AlMe(3) are also consistent with this, indicating that alkylation at the Sc centre does not occur except in the presence of co-catalyst [Ph(3)C][Al{OC(CF(3))(3)}(4)] and the α-alkene, hex-1-ene.