Time-Resolved Infrared Spectroscopy Reveals the pH-Independence of the First Electron Transfer Step in the [FeFe] Hydrogenase Catalytic Cycle.

[FeFe] hydrogenases are highly active catalysts for hydrogen conversion. Their active site has two components: a [4Fe-4S] electron relay covalently attached to the H binding site and a diiron cluster ligated by CO, CN, and 2-azapropane-1,3-dithiolate (ADT) ligands. Reduction of the [4Fe-4S] site was proposed to be coupled with protonation of one of its cysteine ligands.

Umpolung in a Pair of Cobalt(III) Terminal Imido/Imidyl Complexes.

Reaction of the Co complex [(TIMMN )Co ](PF ) (1) (TIMMN =tris-[2-(3-mesityl-imidazolin-2-ylidene)-methyl]amine) with mesityl azide yields the Co imide [(TIMMN )Co (NMes)](PF ) (2). Oxidation of 2 with [FeCp ](PF ) provides access to a rare Co imidyl [(TIMMN )Co(NMes)](PF ) (3). Single-crystal X-ray diffractometry and EPR spectroscopy confirm the molecular structure of 3 and its S= ground state.

Electrochemical evaluation of the de-/re-activation of oxygen evolving Ir oxide.

Understanding the influence of dynamic and stationary polarization on the deactivation of state-of-the-art IrO catalysts is imperative for the design and operation of robust and efficient proton exchange membrane water electrolyzers. In this work, the deactivation and activity regeneration of a commercial IrO catalyst were investigated under potentiodynamic and potentiostatic conditions in acidic media using rotating disk electrode and electrogravimetry methods. Systematic electrochemical protocols were designed to decouple reversible from irreversible activity losses.

Directed Dehydration as Synthetic Tool for Generation of a New Na SnS Polymorph: Crystal Structure, Na Conductivity, and Influence of Sb-Substitution.

We present the convenient synthesis and characterization of the new ternary thiostannate Na SnS (space group ) by directed removal of crystal water molecules from Na SnS ⋅14 H O. The compound represents a new kinetically stable polymorph of Na SnS , which is transformed into the known, thermodynamically stable form (space group ) at elevated temperatures. Thermal co-decomposition of mixtures with Na SbS ⋅9 H O generates solid solution products Na Sn Sb S (x=0.

Antisymmetric Spin Exchange in a μ-1,2-Peroxodicopper(II) Complex with an Orthogonal Cu-O-O-Cu Arrangement and = 1 Spin Ground State Characterized by THz-EPR.

A unique type of Cu/O adduct with orthogonal (close to 90°) Cu-O-O-Cu arrangement has been proposed for initial stages of O binding at biological type III dicopper sites, and targeted ligand design has now allowed us to emulate such an adduct in a pyrazolate-based μη η-peroxodicopper(II) complex () with Cu-O-O-Cu torsion φ of 87°, coined intermediate. Full characterization of , including X-ray diffraction ( = 1.452 Å) and Raman spectroscopy (ν̃ = 807 cm), completes a series of closely related Cu/O intermediates featuring μη η-peroxodicopper(II) cores with φ ranging from 55° (, -peroxo ; Brinkmeier A.

Milliwatt three- and four-pulse double electron electron resonance for protein structure determination.

Electron paramagnetic resonance (EPR) experiments for protein structure determination using double electron-electron resonance (DEER) spectroscopy rely on high-power microwave amplifiers (>300 W) to create the short pulse lengths needed to excite a sizable portion of the spectrum. The recently introduced self-resonant microhelix combines a high conversion efficiency with an intrinsically large bandwidth (low -value) and a high absolute sensitivity. We report dead times in 3-pulse DEER experiments as low as 14 ± 2 ns achieved using less than 1 W of power at X-band (nominally 9.

Rhodium(i) complexes derived from tris(isopropyl)-azaphosphatrane-controlling the metal-ligand interplay.

Proazaphosphatranes are intriguing ligand architectures comprising a bicyclic cage of flexible nature. They can undergo structural deformations due to transannulation while displaying modular electronic and steric properties. Herein, we report the synthesis and coordination chemistry of rhodium(i) complexes bearing a tris(isopropyl)-azaphosphatrane (TPrAP) ligand.

Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer-Tropsch Synthesis and Reductive Hydroformylation.

The selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer-Tropsch and molecular hydroformylation catalysts in a one-pot slurry-phase process. Unprecedented selectivities (>50 wt %) to C alcohols are achieved at CO conversion levels >70 %, alongside negligible CO side-production.

FAIR data enabling new horizons for materials research.

The prosperity and lifestyle of our society are very much governed by achievements in condensed matter physics, chemistry and materials science, because new products for sectors such as energy, the environment, health, mobility and information technology (IT) rely largely on improved or even new materials. Examples include solid-state lighting, touchscreens, batteries, implants, drug delivery and many more. The enormous amount of research data produced every day in these fields represents a gold mine of the twenty-first century.

Red edge effect and chromoselective photocatalysis with amorphous covalent triazine-based frameworks.

Chromoselective photocatalysis offers an intriguing opportunity to enable a specific reaction pathway out of a potentially possible multiplicity for a given substrate by using a sensitizer that converts the energy of incident photon into the redox potential of the corresponding magnitude. Several sensitizers possessing different discrete redox potentials (high/low) upon excitation with photons of specific wavelength (short/long) have been reported. Herein, we report design of molecular structures of two-dimensional amorphous covalent triazine-based frameworks (CTFs) possessing intraband states close to the valence band with strong red edge effect (REE).

A conformational role for NifW in the maturation of molybdenum nitrogenase P-cluster.

Reduction of dinitrogen by molybdenum nitrogenase relies on complex metalloclusters: the [8Fe:7S] P-cluster and the [7Fe:9S:Mo:C:homocitrate] FeMo-cofactor. Although both clusters bear topological similarities and require the reductive fusion of [4Fe:4S] sub-clusters to achieve their respective assemblies, P-clusters are assembled directly on the NifDK polypeptide prior to the insertion of FeMo-co, which is fully assembled separately from NifDK. P-cluster maturation involves the iron protein NifH as well as several accessory proteins, whose role has not been elucidated.

Electrocatalytic Semihydrogenation of Alkynes with [Ni(bpy)].

Electrifying the production of base and fine chemicals calls for the development of electrocatalytic methodologies for these transformations. We show here that the semihydrogenation of alkynes, an important transformation in organic synthesis, is electrocatalyzed at room temperature by a simple complex of earth-abundant nickel, [Ni(bpy)]. The approach operates under mild conditions and is selective toward the semihydrogenated olefins with good to very good isomer stereoselectivity.

Auto-Tandem Catalytic Reductive Hydroformylation in a CO-Switchable Solvent System.

Upgradation of olefin-enriched Fischer-Tropsch cuts by the synthesis of alcohols leads to drop-in-capable biosynthetic fuels with low carbon emissions. As an alternative to the conventional two-step production of long-chain alcohols, tandem catalytic systems improve the energy and resource efficiency. Herein, we present an auto-tandem catalytic system for the production of alcohols from olefin-paraffin mixtures.

Insights into the electronic structure of hydroxyl on Ag(110) under near ambient conditions.

Adsorbed hydroxyl is a key intermediate present in many catalytic reactions and electrochemical processes. In particular, hydroxyl adsorbed on noble metal surfaces has attracted attention due to its role in water-gas shift, selective oxidation of hydrocarbons and water splitting. In this work, from a well-defined oxygen covered Ag(110) surface with O-(2 × 1) reconstruction, we prepared a fully hydroxylated surface phase in equilibrium with water and oxygen in the gas phase under near ambient conditions.

X-ray Absorption Near-Edge Structure (XANES) at the O -Edge of Bulk CoO: Experimental and Theoretical Studies.

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co3O4). Specifically, we analyse the oxygen -edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment.

Single-Electron Oxidation of Carbene-Coordinated Pnictinidenes-Entry into Heteroleptic Radical Cations and Metalloid Clusters.

Stable heavy main group element radicals are challenging synthetic targets. Although several strategies have been developed to stabilize such odd-electron species, the number of heavier pnictogen-centered radicals is limited. We report on a series of two-coordinated pnictogen-centered radical cations [(cAAC)EGa(Cl)L][B(CF)] (cAAC = [HC(CMe)NDipp]C; Dipp = 2,6--PrCH; E = As , Sb , Bi ; L = HC[C(Me)NDipp]) synthesized by one-electron oxidation of L(Cl)Ga-substituted pnictinidenes (cAAC)EGa(Cl)L (E = As , Sb , Bi ).

Properties of Bulk In-Pt Intermetallic Compounds in Methanol Steam Reforming.

Heterogeneous catalysts are often complex materials containing different compounds. While this can lead to highly beneficial interfaces, it is difficult to identify the role of single components. In methanol steam reforming (MSR), the interplay between intermetallic compounds, supporting oxides and redox reactions leads to highly active and CO -selective materials.

Synthesis and redox activity of carbene-coordinated group 13 metal radicals.

Carbenes are known to stabilize main group element compounds with unusual electronic properties. Herein, we report the synthesis of carbene-stabilized group 13 metal radicals (cAAC)MX(IPr) (M = Al, X = Br 3; M = Ga, X = Cl 4) and the corresponding cations [(cAAC)MX(IPr)][B(CF)] (M = Al, X = Br 5; M = Ga, X = Cl 6), which were characterized spectroscopically and by sc-XRD. Quantum chemical calculation gave insights into their electronic structures.

Sequential Reduction of Borylstibane to an Electronically Nonsymmetric Diboryldistibene Radical Anion.

Understanding the formation of metal-metal bonds and their electronic structures is still a scientific task. We herein report on the stepwise synthesis of boryl-substituted antimony compounds in which the antimony atoms adopt four different oxidation states (+III, +II, +I, +I/0). Sb-C bond homolysis of Cp*[(HCNDip)B]SbCl (; Cp* = CMe; Dip = 2,6-PrCH) gave diboryldichlorodistibane [(HCNDip)BSbCl] (), which reacted with KC to form diboryldistibene [(HCNDip)BSb] () and traces of cyclotetrastibane [(HCNDip)B]SbCl ().

Primary donor triplet states of Photosystem I and II studied by Q-band pulse ENDOR spectroscopy.

The photoexcited triplet state of the "primary donors" in the two photosystems of oxygenic photosynthesis has been investigated by means of electron-nuclear double resonance (ENDOR) at Q-band (34 GHz). The data obtained represent the first set of H hyperfine coupling tensors of the P700 triplet state in PSI and expand the existing data set for P680. We achieved an extensive assignment of the observed electron-nuclear hyperfine coupling constants (hfcs) corresponding to the methine α-protons and the methyl group β-protons of the chlorophyll (Chl) macrocycle.

Synthesis of Fe and Fe Cyanide Complexes Using Hypervalent Iodine Reagents as Cyano-Transfer One-Electron Oxidants.

We disclose a new reactivity mode for electrophilic cyano λ -iodanes as group transfer one-electron oxidants to synthesize Fe and Fe cyanide complexes. The inherent thermal instability of high-valent Fe compounds without π-donor ligands (such as oxido (O ), imido (RN ) or nitrido (N )) makes their isolation and structural characterization a very challenging task. We report the synthesis of an Fe cyanide complex [(N N')FeCN] (4) by two consecutive single electron transfer (SET) processes from Fe precursor [(N N')FeLi(THF)] (1) with cyanobenziodoxolone (CBX).

Semi-Crystalline Polyoxymethylene--Polyoxyalkylene Multi-Block Telechels as Building Blocks for Polyurethane Applications.

Hydroxy-terminated polyoxymethylene--polyoxyalkylene multi-block telechels were obtained by a new methodology that allows for the formal substituting of ether units in polyether polyols with oxymethylene moieties. An interesting feature is that, unlike carbonate groups in polycarbonate and polyethercarbonate polyols, homopolymer blocks of polyoxymethylene moieties can be formed. The regular nature of polyoxymethylene blocks imparts a certain crystallinity to the polymer that can give rise to new properties of polyurethanes derived from such telechels.

Stability of the H-cluster under whole-cell conditions-formation of an H-like state and its reactivity towards oxygen.

Hydrogenases are metalloenzymes that catalyze the reversible oxidation of molecular hydrogen into protons and electrons. For this purpose, [FeFe]-hydrogenases utilize a hexanuclear iron cofactor, the H-cluster. This biologically unique cofactor provides the enzyme with outstanding catalytic activities, but it is also highly oxygen sensitive.

Analysis of the Geometric and Electronic Structure of Spin-Coupled Iron-Sulfur Dimers with Broken-Symmetry DFT: Implications for FeMoco.

The open-shell electronic structure of iron-sulfur clusters presents considerable challenges to quantum chemistry, with the complex iron-molybdenum cofactor (FeMoco) of nitrogenase representing perhaps the ultimate challenge for either wavefunction or density functional theory. While broken-symmetry density functional theory has seen some success in describing the electronic structure of such cofactors, there is a large exchange-correlation functional dependence in calculations that is not fully understood. In this work, we present a geometric benchmarking test set, FeMoD11, of synthetic spin-coupled Fe-Fe and Mo-Fe dimers, with relevance to the molecular and electronic structure of the Mo-nitrogenase FeMo cofactor.