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Employing the newly developed, hepta-dentate tris(aryloxide) ligand cyclen(Me)(t-Bu,t-BuArOH)3 provides controlled access to the first U(iv/v) hydroxido and U(iv/v/vi) oxido complex pairs in a retained ligand environment.

Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a...

The facile synthesis of the first bis‐N‐heterocyclic imine‐stabilized chlorosilyliumylidene 1 is reported. Remarkably, consecutive reaction of 1 with PPh3AuCl and K2Fe(CO)4 gives rise to the unique heterobimetallic complex 1,2‐(MesNHI)2‐C2H4‐ClSiAuFe(CO)4 (4). The overall neutral complex 4 bears an unusual linear Si−Au−Fe structure and a rare anagostic interaction between the d 10‐configured gold atom and a CH bond of the mesityl ligand. According to the computational analysis and 57Fe Mössbauer spectroscopy, the formal Fe‐oxidation state remains at −II. Thus, the electronic structure of 4 is best described as an overall neutral—yet zwitterionic—heterobimetallic “Si(II)+‐Au(I)+‐Fe(‐II)2−”‐silyliumylidene complex, derived from double anion exchange. The computational analysis indicates strong hyperconjugative back donation from the gold(I) atom to the silyliumylidene ligand., The selective synthesis of a silyliumylidene‐stabilized mononuclear Au−Fe complex, by a convenient one‐pot reaction starting from bis‐NHI silyliumylidene chloride, is reported. X‐ray crystallography, IR and 57Fe Mössbauer spectroscopy, as well as computations suggest a zwitterionic Si(II)+−Au(I)+−Fe(‐II)2− bonding motif with rare anagostic CH⋅⋅⋅Au contacts and considerable backbonding capabilities of the silyliumylidene.

With a view to developing multimetallic molecular catalysts that mimic the oxygen‐evolving catalyst (OEC) in Nature's photosystem II, the synthesis of various dicubanoid manganese clusters is described and their catalytic activity investigated for water oxidation in basic, aqueous solution. Pyridinemethanol‐based ligands are known to support polynuclear and cubanoid structures in manganese coordination chemistry. The chelators 2,6‐pyridinedimethanol (H2L1) and 6‐methyl‐2‐pyridinemethanol (HL2) were chosen to yield polynuclear manganese complexes; namely, the tetranuclear defective dicubanes [MnII 2MnIII 2(HL1)4(OAc)4(OMe)2] and [MnII 2MnIII 2(HL1)6(OAc)2] (OAc)2⋅2 H2O, as well as the octanuclear‐dicubanoid [MnII 6MnIII 2(L2)4(O)2(OAc)10(HOMe/OH2)2]⋅3MeOH⋅MeCN. In freshly prepared solutions, polynuclear species were detected by electrospray ionization mass spectrometry, whereas X‐band electron paramagnetic resonance studies in dilute, liquid solution suggested the presence of divalent mononuclear Mn species with g values of 2. However, the magnetochemical investigation of the complexes’ solutions by the Evans technique confirmed a haphazard combination of manganese coordination complexes, from mononuclear to polynuclear species. Subsequently, the newly synthesized and characterized manganese molecular complexes were employed as precursors to prepare electrode‐deposited films in a buffer‐free solution to evaluate and compare their stability and catalytic activity for water oxidation electrocatalysis., Film star: Cubanoid tetranuclear and octanuclear manganese complexes are synthesized and electrodeposited on an active surface to compare their electrocatalytic activity for the water oxidation reaction. A simple, direct relationship is derived between the manganese content in the precursor and the oxygen evolution activity of the deposited films.

In recent years, the defect engineering of titania via reduction treatments has shown a high potential for enabling efficient and co-catalyst-free photocatalytic H2 generation from methanol/water solutions. However, defect engineering simultaneously alters several properties of TiO2. Here, we use pristine (white) and hydrogenated (gray) anatase nanosheets with dominant (001) facets. By comparing electrical conductivity, photocurrent spectra, transient photocurrent response, and photocatalytic H2 evolution, we show that the increased conductivity or broad visible light absorption of gray titania is not responsible for its increased activity. Instead, the true bottleneck is the hole transfer rate that is significantly accelerated while using gray instead of white modification. Moreover, the hole transfer reaction causes the accumulation of the reaction products in pure water, hindering the photocatalytic H2 evolution over time. These combined factors explain the superior performance of gray titania over white titania in photoelectrochemical or photocatalytic water splitting.

The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n-dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e., the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF6]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG2)2Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.

The "metathesis reaction" is a straightforward and often metal-catalyzed chemical reaction that transforms two hydrocarbon molecules to two new hydrocarbons by exchange of molecular fragments. Alkane, alkene and alkyne metathesis have become an important tool in synthetic chemistry and have provided access to complex organic structures. Since the discovery of industrial olefin metathesis in the 1960s, many modifications have been reported; thus, increasing scope and improving reaction selectivity. Olefin metathesis catalysts based on high-valent group six elements or Ru(IV) have been developed and improved through ligand modifications. In addition, significant effort was invested to realize olefin metathesis with a non-toxic, bio-compatible and one of the most abundant elements in the earth ' s crust; namely, iron. First evidences suggest that low-valent Fe(II) complexes are active in olefin metathesis. Although the latter has not been unambiguously established, this review summarizes the key advances in the field and aims to guide through the challenges., Chemistry - A European Journal, 28 (62), ISSN:0947-6539, ISSN:1521-3765

We describe a new type of nitrogen‐centered polycyclic scaffold comprising a unique combination of 5‐, 6‐, and 7‐membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1‐naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3‐fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X‐ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density‐functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.

Die Umsetzung des CoI-Komplexes [(TIMMNmes)CoI](PF6) (1) (TIMMNmes=tris-[2-(3-Mesityl-imidazolin-2-yliden)-methyl]amin) mit Mesitylazid ergibt das CoIII-Imid [(TIMMNmes)CoIII(NMes)](PF6) (2). Folgende Oxidation mit [FeCp2](PF6) ermöglicht den Zugang zu dem seltenen CoIII-Imidylkomplex [(TIMMNmes)Co(NMes)](PF6)2 (3). Einkristall-Röntgenstrukturanalyse und ESR-Spektroskopie bestätigen die molekulare Struktur von 3 und seinen S=urn:x-wiley:00448249:media:ange202206848:ange202206848-math-0001 Grundzustand. ENDOR, Röntgenabsorptionsspektroskopie und quantenchemische Rechnungen belegen eine ligandenbasierte Oxidation und damit eine Imidyl-radikalische elektronische Struktur für 3. Die Insertion einer verfügbaren NHC-Einheit in den Imidoliganden in 2 ergibt innerhalb 12 Stunden das CoI-N-heterocyclische Imin 4. Im Gegensatz dazu dauert es nur eine halbe Stunde, bis sich 3 in das CoII-Kongener 5 umsetzt. Es wurde weiterhin festgestellt, dass die Insertionsreaktion von 2 zu 4 durch einen nukleophilen Angriff des Imidoliganden am NHC erfolgt, wohingegen sich 3 zu 5 durch einen nukleophilen Angriff des NHCs am elektrophilen Imidylliganden umsetzt. Der Reaktivitätswechsel bei der Oxidation von 2 zu 3 bestätigt eine Umpolung des Imidoliganden.

We report the synthesis of a unique cubic metal–organic framework (MOF), Fe‐HHTP‐MOF, comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions, arranged in a diamond topology. The MOF is synthesized under solvothermal conditions, yielding a highly crystalline, deep black powder, with crystallites of 300–500 nm size and tetrahedral morphology. Nitrogen sorption analysis indicates a highly porous material with a surface area exceeding 1400 m2 g−1. Furthermore, Fe‐HHTP‐MOF shows broadband absorption from 475 up to 1900 nm with excellent absorption capability of 98.5 % of the incoming light over the visible spectral region. Electrical conductivity measurements of pressed pellets reveal a high intrinsic electrical conductivity of up to 10−3 S cm−1. Quantum mechanical calculations predict Fe‐HHTP‐MOF to be an efficient electron conductor, exhibiting continuous charge‐carrier pathways throughout the structure., Fe‐HHTP‐MOF, a unique cubic metal–organic framework (MOF) comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions arranged in a diamond topology is reported. Fe‐HHTP‐MOF is a highly crystalline, porous and deep black material featuring high electrical conductivity.

The reaction of the cobalt(I) complex [(TIMMNmes)CoI](BPh4) (2) (TIMMNmes=tris‐[2‐(3‐mesitylimidazolin‐2‐ylidene)methyl]amine) with 1‐adamantylazide yields the cobalt(III) imido complex [(TIMMNmes)CoIII(NAd)](BPh4) (3) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z2)‐orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One‐electron oxidation of 3 with [FeCp2](OTf) provides access to the rare, high‐valent cobalt(IV) imido complex [(TIMMNmes)CoIV(NAd)](OTf)2 (4). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2 , electron configuration. A computational analysis of 4 suggests high covalency within the CoIV=NAd bond with non‐negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character., Straightforward access to a cobalt(IV) terminal imido complex was provided by one‐electron oxidation of a cobalt(III) terminal imido precursor. The cobalt(IV) monoimido complex could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2 , electron configuration.

Lithium trimethylsilyldiazomethanide and a cobalt (II) precursor with an N-anchored tris-NHC (TIMENmes ) ligand provide access to the cobalt nitrilimide 1. Complex 1 was structurally characterized by single-crystal X-ray diffractometry (SC-XRD) and its electronic structure was examined in detail, including EPR spectroscopy, SQUID magnetometry and computational analyses. The desilylation of the C-(trimethylsilyl)nitrilimide reveals a transient complex with an elusive diazomethanediide ligand, which substitutes one of the mesitylene rings of the ancillary ligand through C-N bond cleavage. This transformation results in the cyclometalated cobalt(II) complex 2, featuring a rare isocyanoamido-κ-C ligand.

Lithium trimethylsilyldiazomethanide and a cobalt (II) precursor with an N‐anchored tris‐NHC (TIMENmes) ligand provide access to the cobalt nitrilimide 1. Complex 1 was structurally characterized by single‐crystal X‐ray diffractometry (SC‐XRD) and its electronic structure was examined in detail, including EPR spectroscopy, SQUID magnetometry and computational analyses. The desilylation of the C‐(trimethylsilyl)nitrilimide reveals a transient complex with an elusive diazomethanediide ligand, which substitutes one of the mesitylene rings of the ancillary ligand through C−N bond cleavage. This transformation results in the cyclometalated cobalt(II) complex 2, featuring a rare isocyanoamido‐κ‐C ligand., Trimethylsilylium abstraction from a cobalt nitrilimide complex generates a transient cobalt diazomethanediide complex, which forms a terminal isocyanoamido ligand through a radical de‐arylation.

Three linear dimers with two redox‐active planarized triphenylamines were synthesized and their structures verified by X‐ray crystallography. Their radical cations, which exhibit electron self‐exchange between the two redox centers, are of great interest. This process was thoroughly investigated by means of electron paramagnetic resonance spectroscopy, absorption spectroscopy, and (time‐dependent) density functional theory calculations. A comparison of the key parameters of electron transfer with non‐planarized nitrogen‐centered building blocks emphasizes the impact of using redox centers with low internal reorganization energies. However, the distance‐dependence attenuation factor of the super‐exchange mechanisms remains similar., Novel building blocks for mixed‐valence charge‐transfer compounds: Planar N‐heterotriangulene dimers with low reorganization energies and activation barriers for electron self‐exchange have been synthesized and characterized.

We report high‐valent iron complexes supported by N‐heterocyclic carbene (NHC)‐anchored, bis‐phenolate pincer ligands that undergo ligand‐to‐metal charge transfer (LMCT) upon photoexcitation. The resulting excited states – with a lifetime in the picosecond range – feature a ligand‐based, mixed‐valence system and intense intervalence charge transfer bands in the near‐infrared region. Upon oxidation of the complex, corresponding intervalence charge transfer absorptions are also observed in the ground state. We suggest that the spectroscopic hallmarks of such LMCT states provide useful tools to decipher excited‐state decay mechanisms in high‐valent NHC complexes. Our observations further indicate that NHC‐anchored, bis‐phenolate pincer ligands are not sufficiently strong donors to prevent the population of excited metal‐centered states in high‐valent iron complexes.

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)2C2P2 (1) (IPr=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe2CO9] gives the neutral iron tricarbonyl complex [Fe(CO)3-η3-{(IPr)2C2P2}] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2](BArF24), affords the dicationic tricarbonyl complex [Fe(CO)3-η4-{(IPr)2C2P2}](BArF24)2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2-η4-{(IPr)2C2P2}](BArF24) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2-η4-{(IPr)2C2P2}] (6). An analysis by various spectroscopic techniques (57Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade–Mingos clusters., Angewandte Chemie. International Edition, 61 (43), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Using the potentially tridentate

The open-shell iron pentacarbonyl cation [Fe(CO)

Reaction of the Co

Addition of the bipyridyl-embedded cycloparaphenylene nanohoop bipy[9]CPP to [Fe{H2 B(pyz)2 }] (pyz=pyrazolyl) produces the distorted octahedral complex [Fe(bipy[9]CPP){H2 B(pyz)2 }2 ] (1). The molecular structure of 1 shows that the nanohoop ligand contains a non-planar bipy unit. Magnetic susceptibility measurements indicate spin-crossover (SCO) behaviour with a T1/2 of 130 K, lower than that of 160 K observed with the related compound [Fe(bipy){H2 B(pyz)2 }2 ] (2), which contains a conventional bipy ligand. A computational study of 1 and 2 reveals that the curvature of the nanohoop leads to the different SCO properties, suggesting that the SCO behaviour of iron(II) can be tuned by varying the size and diameter of the nanohoop.

[Image: see text] A high-spin, mononuclear Ti(II) complex, [(Tp(tBu,Me))TiCl] [Tp(tBu,Me–) = hydridotris(3-tert-butyl-5-methylpyrazol-1-yl)borate], confined to a tetrahedral ligand-field environment, has been prepared by reduction of the precursor [(Tp(tBu,Me))TiCl(2)] with KC(8). Complex [(Tp(tBu,Me))TiCl] has a (3)A(2) ground state (assuming C(3v) symmetry based on structural studies), established via a combination of high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy, solution and solid-state magnetic studies, Ti K-edge X-ray absorption spectroscopy (XAS), and both density functional theory and ab initio (complete-active-space self-consistent-field, CASSCF) calculations. The formally and physically defined Ti(II) complex readily binds tetrahydrofuran (THF) to form the paramagnetic adduct [(Tp(tBu,Me))TiCl(THF)], which is impervious to N(2) binding. However, in the absence of THF, the Ti(II) complex captures N(2) to produce the diamagnetic complex [(Tp(tBu,Me))TiCl](2)(η(1),η(1);μ(2)-N(2)), with a linear Ti=N=N=Ti topology, established by single-crystal X-ray diffraction. The N(2) complex was characterized using XAS as well as IR and Raman spectroscopies, thus establishing this complex to possess two Ti(III) centers covalently bridged by an N(2)(2–) unit. A π acid such as CNAd (Ad = 1-adamantyl) coordinates to [(Tp(tBu,Me))TiCl] without inducing spin pairing of the d electrons, thereby forming a unique high-spin and five-coordinate Ti(II) complex, namely, [(Tp(tBu,Me))TiCl(CNAd)]. The reducing power of the coordinatively unsaturated Ti(II)-containing [(Τp(tBu,Me))TiCl] species, quantified by electrochemistry, provides access to a family of mononuclear Ti(IV) complexes of the type [(Tp(tBu,Me))Ti=E(Cl)] (with E(2–) = NSiMe(3), N(2)CPh(2), O, and NH) by virtue of atom- or group-transfer reactions using various small molecules such as N(3)SiMe(3), N(2)CPh(2), N(2)O, and the bicyclic amine 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene.

We have synthesized and characterized Co(II) (1), Zn(II) (2), Fe(III) (3) and Cu(II) (4) complexes of 2,2'‐[2,6‐pyridinediylbis(ethylidyne‐1‐hydrazinyl‐2‐ylidene)]bis[N,N,N‐trimethyl‐2‐oxoethanaminium] dichloride (H2LCl2) by NMR, IR, and X‐Band EPR spectroscopy, respectively, as well as by single‐crystal X‐ray structural analysis. H2LCl2 belongs to the class of diacetylpyridine bis(hydrazone) ligands and bears two positively charged quaternary ammonium functionalities. The complexes 1–3 possess a pentagonal‐bipyramidal geometry, whereas 4 has square‐pyramidal geometry. Redox reactivity and SOD activity of the complexes was studied by means of electrochemical measurements in aqueous‐buffer and DMF or DMSO solutions, respectively, as well as by stopped‐flow measurements. Complexes 1–3 do not have SOD activity, whereas 4 exhibits a high catalytic rate constant for the superoxide dismutation, kcat = 1.73 × 107 m–1 s–1 (in MOPS buffer solution of pH = 7.4). The results were discussed in terms of complex redox potentials, electrostatic interactions and their spatial distribution, kinetic lability of metal centers, and stability of peroxo intermediates, respectively.

A feeding experiment was carried out with late-lactating cows over 12 weeks to evaluate the feeding value of a basic diet with maize and grass silage (MS, GS) when combined with varying portions of concentrate in the ration (20% and 60% on a dry matter basis) and to test the effects on health and performance, the transfer of important Fusarium toxins to blood and milk, the total and Shiga toxin (stx)-forming E. coli counts, and the presence of Clostridium botulinum neurotoxin (BoNT) genes in rectal fecal samples. MS was contaminated by a broader spectrum of fungal and other metabolites compared to GS. MS contained higher concentrations of the important Fusarium toxins deoxynivalenol (DON) and zearalenone (ZEN). Blood and milk levels of DON and ZEN residues generally reflected the differences in exposure at a low level. Feeding of MS with 60% concentrate feed induced subacute ruminal acidosis (SARA) associated with a marked drop in dry matter intake, fat corrected milk yield and a fat to protein ratio in milk of lower than 1. The SARA-associated higher ruminal LPS concentration did not affect the circulating concentrations of haptoglobin as an indicator of systemic inflammation. Lower rumen pH values in both MS-fed groups were associated with lower pH values, higher absolute E. coli counts and increased proportions of stx-positive E. coli in rectal feces. BoNT genes A, B, C, D, E and F remained undetectable in any of the fecal samples suggesting that feedstuffs were virtually free of the corresponding C. botulinum strains. In conclusion, maize feedstuff (silage, grains, starch-containing byproducts)-dominated rations for dairy cows should be avoided to reduce adverse effects on health and food safety.

Adding to the versatile class of ionic liquids, we report the detailed structure and property analysis of a new class of asymmetrically substituted imidazolium salts, offering interesting thermal characteristics, such as liquid crystalline behavior, polymorphism or glass transitions. A scalable general synthetic procedure for N-polyaryl-N’-alkyl-functionalized imidazolium salts with para-substituted linker (L) moieties at the aryl chain, namely [LPhmImHR]+ (L=Br, CN, SMe, CO2Et, OH; m=2, 3; R=C12, PEGn; n=2, 3, 4), was developed. These imidazolium salts were studied by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy and thermochemical methods (DSC, TGA). Furthermore, these imidazolium salts were used as N-heterocyclic carbene (NHC) ligand precursors for mononuclear, first-row transition metal complexes (MnII, FeII, CoII, NiII, ZnII, CuI, AgI, AuI) and for the dinuclear Ti-supported Fe-NHC complex [(OPy)2Ti(OPh2ImC12)2(FeI2)] (OPy=pyridin-2-ylmethanolate). The complexes were studied concerning their structural and magnetic behavior via multi-nuclear NMR spectroscopy, SC-XRD analyses, variable temperature and field-dependent (VT-VF) SQUID magnetization methods, X-band EPR spectroscopy and, where appropriate, zero-field 57Fe Mössbauer spectroscopy.

Reactions of di‐tert‐butyldiphosphatetrahedrane (1) with cycloocta‐1,5‐diene‐ or anthracene‐stabilised metalate anions of iron and cobalt consistently afford complexes of the rarely encountered 1,2‐diphosphacyclobutadiene ligand, which have previously been very challenging synthetic targets. The subsequent reactivity of 1,2‐diphosphacyclobutadiene cobaltates toward various electrophiles has also been investigated and is compared to reactions of related 1,3‐diphosphacyclobutadiene complexes. The results highlight the distinct reactivity of such isomeric species, showing that the 1,2‐isomers can act as precursors for previously unknown triphospholium ligands. The electronic structures of the new complexes were investigated by several methods, including NMR, EPR and Mößbauer spectroscopies as well as quantum chemical calculations., Reactions of iron and cobalt metalates with di‐tert‐butyldiphosphatetrahedrane readily afford 1,2‐diphosphacyclobutadiene complexes. The corresponding 1,3‐isomers were accessed by dimerisation of tert‐butylphosphaalkyne on the metal centre. The reactivity of 1,2‐ and 1,3‐diphosphacyclobutadiene cobaltates toward electrophiles was studied and the electronic structures of the new metalates were investigated by spectroscopy and quantum chemical calculations.

Defined substoichiometric titanium oxides (Ti$_x$O$_{2x-1}$ with $3 < x < 10$) called Magneli phases have been investigated mostly for their unusual high conductivity and metal-like behavior. In photocatalysis, Magneli phase containing titania particles have been reported to provide favorable charge separation resulting in enhanced reaction efficiency. In the current work we describe a one-step synthesis of Magneli-containing mixed phase nanoparticles that carry directly integrated minute amounts of Pt. Phase optimized nanoparticles that contain only a few hundred ppm Pt are very effective photocatalysts for H$_2$ evolution (they provide a 50-100 times higher H$_2$ evolution than plain anatase loaded with a similar amount of Pt). These photocatalysts are synthesized in a setup combining a hot-wall reactor that is used for TiOx synthesis with a spark generator producing Pt nanoparticles. Different reactor temperatures result in various phase ratios between anatase and Magneli phases. The titania nanoparticles (ca. 24 - 53 nm) were characterized using XRD, HRTEM, XPS and EPR spectra as well as ICP-OES analysis. The best photocatalyst prepared at 900$^\circ$C (which consists of mixed phase particles of 32% anatase, 11% rutile and 57% Magneli phases loaded with 290 ppm of Pt) can provide a photocatalytic H$_2$ evolution rate of ca. 5432 micromol h$^{-1} g$^{-1}$ for UV and ca. 1670 micromol h$^{-1} g$^{-1}$ for AM1.5 illumination. For powders converted to higher amounts of Magneli phases (1000$^\circ$C and 1100$^\circ$C), a drastic loss of the photocatalytic H$_2$ generation activity is observed. Thus, the high photocatalytic efficiency under best conditions is ascribed to an effective synergy between multi-junctions of Magneli titania and Pt that enable a much more effective charge separation and reaction than conventional Pt/anatase junctions.

A novel method for the N−N bond cleavage of trimethylsilyl diazomethane is reported for the synthesis of terminal nitride complexes. The lithium salt of trimethylsilyl diazomethane was used to generate a rare terminal nitrilimine transition metal complex with partially occupied d‐orbitals. This iron complex 2 was characterized by CHN combustion analysis, 1H and 13C NMR spectroscopic analysis, single‐crystal X‐ray crystallography, SQUID magnetometry, 57Fe Mössbauer spectroscopy, and computational analysis. The combined results suggest a high‐spin d 6 (S=2) electronic configuration and an allenic structure of the nitrilimine ligand. Reduction of 2 results in release of the nitrilimine ligand and formation of the iron(I) complex 3, which was characterized by CHN combustion analysis, 1H NMR spectroscopic analysis, and single‐crystal X‐ray crystallography. Treatment of 2 with fluoride salts quantitatively yields the diamagnetic FeIV nitride complex 4, with concomitant formation of cyanide and trimethylsilyl fluoride through N−N bond cleavage., Chain reaction: A fluoride salt cleaves the N–N bond of an iron trimethylsilyl nitrilimine complex and generates the terminal nitride, fluorotrimethylsilane, and cyanide. The complementary reactivity of nitrilimine and azido ligands provides a new approach for the synthesis of metal terminal nitrido complexes.

In the present work, we show how illumination of anatase in an aqueous methanolic solution forms Ti3+ sites that are catalytically active for the generation of dihydrogen (H2). With an increasing illumination time, a light-induced self-amplification of the photocatalytic H2 production rate can be observed. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. Combined measurements of H2 generation rates and in-situ EPR spectroscopic observation over the illumination time with AM 1.5 or UV light establish that the activation is accompanied with the formation of Ti3+ states, which is validated through their characteristic EPR resonance at g=1.93. We show that this self-activation and amplification behavior can be observed for anatase nanoparticles and nanotubes.

Pentavalent uranyl species are crucial intermediates in transformations that play a key role for the nuclear industry and have recently been demonstrated to persist in reducing biotic and abiotic aqueous environments. However, due to the inherent instability of pentavalent uranyl, little is known about its electronic structure. Herein, we report the synthesis and characterization of a series of monomeric and dimeric, pentavalent uranyl amide complexes. These synthetic efforts enable the acquisition of emission spectra of well-defined pentavalent uranyl complexes using photoluminescence techniques, which establish a unique signature to characterize its electronic structure and, potentially, its role in biological and engineered environments via emission spectroscopy.

Recently, black and grey titania in various morphologies have been intensively investigated for their high performance in photocatalytic H2 generation. Here we use titania nanosheets (NSs) with a large percentage of (001) facets and hydrogenate them to activate suitable Ti3+-Ov defects for co-catalyst free H2 generation. Key to a highly active NS-catalyst is the prevention of serious deformation and sintering during the thermal hydrogenation. In this work, we present a systematic investigation of different thermally treated NSs characterized by scanning electron microscope, high resolution-transmission electron microscopy, TEM-energy-dispersive x-ray, x-ray diffraction, electron paramagnetic response, x-ray photoelectron spectroscopy, and photocatalytic H2 evolution performance. We describe how to achieve robust grey NSs with an intact two-dimensional shape that can endure hydrogenation at the required high temperatures. Due to a defined faceting, these optimized ‘grey’ NSs can produce photocatalytic H2 at a higher rate than previously reported best performing grey nanoparticles—this in spite of having a lower Brunauer–Emmett–Teller than the reduced nanoparticles.

Magneli phases of titanium dioxide (such as Ti4O7, Ti5O9, etc.) provide electronic properties, namely a stable metallic behavior at room temperature. In this manuscript, we demonstrate that nanoscopic Magneli phases, formed intrinsically in anatase during a thermal aerosol synthesis, can enable significant photocatalytic H2 generation. This without the use of any extrinsic co-catalyst in anatase. Under optimized conditions, mixed phase particles of 30 percent anatase, 25 percent Ti4O7 and 20 percent Ti5O9 are obtained that can provide, under solar light, direct photocatalytic H2 evolution at a rate of 145 micromol h-1 g-1. These anatase particles contain 5-10 nm size inter-grown phases of Ti4O7 and Ti5O9. Key is the metallic band of Ti4O7 that induces a particle internal charge separation and transfer cascade with suitable energetics and favorable dimensions that are highly effective for H2 generation.

Stable coordination complexes of TiII (3d2) are relatively uncommon, but are of interest as synthons for low oxidation state titanium complexes for application as potential catalysts and reagents for organic synthesis. Specifically, high-spin TiII ions supported by redox-inactive ligands are still quite rare due to the reducing power of this soft ion. Among such TiII complexes is trans-[TiCl2(tmeda)2], where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine. This complex was first reported by Gambarotta and co-workers almost 30 years ago, but it was not spectroscopically characterized and theoretical investigation by quantum chemical theory (QCT) was not feasible at that time. As part of our interest in low oxidation state early transition metal complexes, we have revisited this complex and report a modified synthesis and a low temperature (100 K) crystal structure that differs slightly from that originally reported at ambient temperature. We have used magnetometry, high-frequency and -field EPR (HFEPR), and variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopies to characterize trans-[TiCl2(tmeda)2]. These techniques yield the following S = 1 spin Hamiltonian parameters for the complex: D = -5.23(1) cm-1, E = -0.88(1) cm-1, (E/D = 0.17), g = [1.86(1), 1.94(2), 1.77(1)]. This information, in combination with electronic transitions from MCD, was used as input for both classical ligand-field theory (LFT) and detailed QCT studies, the latter including both density functional theory (DFT) and ab initio methods. These computational methods are seldom applied to paramagnetic early transition metal complexes, particularly those with S > 1/2. Our studies provide a complete picture of the electronic structure of this complex that can be put into context with the few other high-spin and mononuclear TiII species characterized to date.

Summary: Neutral zinc alkoxide complexes show high activity toward the ring-opening polymerization of cyclic esters and carbonates, to generate biodegradable plastics applicable in several areas. Herein, we use a ferrocene-chelating heteroscorpionate complex in redox-switchable polymerization reactions, and we show that it is a moderately active catalyst for the ring-opening polymerization of L-lactide, ɛ-caprolactone, trimethylene carbonate, and δ-valerolactone. Uniquely for this type of catalyst, the oxidized complex has a similar polymerization activity as the corresponding reduced compound, but displays significantly different rates of reaction in the case of trimethylene carbonate and δ-valerolactone. Investigations of the oxidized compound suggest the presence of an organic radical rather than an Fe(III) complex. Electronic structure and density functional theory (DFT) calculations were performed to support the proposed electronic states of the catalytic complex and to help explain the observed reactivity differences. The catalyst was also compared with a monomeric phenoxide complex to show the influence of the phosphine-zinc interaction on catalytic properties. : Chemistry; Inorganic Chemistry; Catalysis; Polymer Chemistry Subject Areas: Chemistry, Inorganic Chemistry, Catalysis, Polymer Chemistry

In a systematic study of the activation of As-4, three [LCo(tol)] (L=beta-diiminato) complexes have revealed different steric and electronic influences. 2,6-Diisopropylphenyl (Dipp) and 2,6-dimethylphenyl (dmp) flanking groups were used, one of the ligands with H backbone substituents (beta-dialdiminate L-0) and two with Me substituents (beta-diketiminates L-3 and L-1). In the reaction with As-4, different dinuclear products [(LCo)(2)As-4] (LM=L-0 (1), L-1 (2), L-3 (3)) were isolated, with all showing differently shaped [Co2As4] cores in the solid state: octahedral in 1, prismatic in 2, and asterane-like in 3. Thermal treatment of 3 leads to the abstraction of one arsenic atom to yield [((LCo)-Co-3)(2)As-3] (4). All products were comprehensively characterized by single-crystal X-ray diffraction, FD-MS, and (HNMR)-H-1 spectroscopy. A rational explanation for the different reactivity is also proposed and DFT calculations shed light on the nature of the highly flexible [Co2As4] cores.

Noble metal cocatalysts are conventionally a crucial factor in oxide-semiconductor-based photocatalytic hydrogen generation. In the present work, we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO3) powder can be used to engineer an intrinsic cocatalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional cocatalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO3[100] single crystal as well as Nb-doped SrTiO3 (100) single crystal. For all types of SrTiO3 samples (nanopowders and either of the single crystals), hydrogenation under optimum conditions leads to a surface-hydroxylated layer together with lattice defects visible by transmission electron microscopy, electron paramagnetic resonance (EPR), and photoluminescence (PL). Active samples provide states in a defective matrix -- this is in contrast to the inactive defects formed in other reductive atmospheres. In aqueous media, active SrTiO3 samples show a significant negative shift of the flatband potential (in photoelectrochemical as well as in capacitance data) and a lower charge-transfer resistance for photoexcited electrons. We therefore ascribe the remarkable cocatalyst-free activation of the material to a synergy between thermodynamics (altered interface energetics induced by hydroxylation) and kinetics (charge transfer mediation by suitable Ti3+ states).

The Por­ta­ble Do­cu­ment For­mat (PDF) is the de-fac­to stan­dard for do­cu­ment ex­chan­ge world­wi­de. To gua­ran­tee the au­then­ti­ci­ty and in­te­gri­ty of do­cu­ments, di­gi­tal si­gna­tu­res are used. Se­ver­al pu­blic and pri­va­te ser­vices ran­ging from go­vern­ments, pu­blic en­t­er­pri­ses, banks, and pay­ment ser­vices rely on the se­cu­ri­ty of PDF si­gna­tu­res. In this paper, we pre­sent the first com­pre­hen­si­ve se­cu­ri­ty eva­lua­ti­on on di­gi­tal si­gna­tu­res in PDFs. We in­tro­du­ce three novel at­tack clas­ses which by­pass the cryp­to­gra­phic pro­tec­tion of di­gi­tal­ly si­gned PDF files al­lowing an at­ta­cker to spoof the con­tent of a si­gned PDF. We ana­ly­zed 22 dif­fe­rent PDF view­ers and found 21 of them to be vul­nerable, in­clu­ding pro­mi­nent and wi­de­ly used ap­p­li­ca­ti­ons such as Adobe Re­a­der DC and Foxit. We ad­di­tio­nal­ly eva­lua­ted eight on­line va­li­da­ti­on ser­vices and found six to be vul­nerable. A pos­si­ble ex­pla­na­ti­on for these re­sults could be the ab­sence of a stan­dard al­go­rithm to ve­ri­fy PDF si­gna­tu­res – each cli­ent ve­ri­fies si­gna­tu­res dif­fer­ent­ly, and at­tacks can be tailo­red to these dif­fe­ren­ces. We, the­re­fo­re, pro­po­se the stan­dar­diza­t­i­on of a se­cu­re ve­ri­fi­ca­ti­on al­go­rithm, which we de­scri­be in this paper. All fin­dings have been re­s­pon­si­bly dis­clo­sed, and the af­fec­ted ven­dors were sup­por­ted du­ring fi­xing the is­su­es. As a re­sult, three ge­ne­ric CVEs for each at­tack class were is­su­ed (CVE-2018-16042, CVE-2018-18688, CVE-2018-18689). Our re­se­arch on PDF si­gna­tu­res and more in­for­ma­ti­on is also on­line avail­able at https://www.pdf-in­se­cu­ri­ty.org/.