Search

The compound Ta4SBr11was prepared by a comproportionation reaction of tantalum bromide with tantalum and elemental sulfur. The crystal structure, as refined by single-crystal X-ray diffraction, is composed of clusters with Ta4S cores, arranged in corrugated van der Waals layers. Individual layers appear to be displaced relative to each other along one direction. Successful crystal growth in a melt of CsBr yielded black platelets of Ta4SBr11, which were used to investigate the electrical properties of the compound. The electronic structure was studied by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and by density functional theory (DFT) band structure calculations, revealing this material to be a small-gap semiconductor. DFT results, in combination with magnetic susceptibility measurements, suggest that metallicity originating from the one unpaired Ta d electron per cluster is most likely suppressed by electronic correlations, forming a cluster Mott insulator.

A novel and more efficient synthesis of Cu3(C3N6H3) is presented through a salt-metathesis reaction using copper(I) chloride and sodium hydrogen cyanamide. This synthesis yields a melaminate trianion through the cyclotrimerization of (HNCN)−ions, offering an alternative route to the deprotonation of melamine for synthesizing melaminate. The reaction is analyzed via differential thermal analysis. After the unconventional formation of this MOF-like structure by solid-state reaction, this material still requires treatment via solvent exchange and vacuum drying due to the presence of a host molecule inside the channels of the structure. The process and the impact of the treatment of Cu3(C3N6H3) on its XRD pattern are thoroughly discussed. Additionally, results from stability, NMR and infrared spectroscopy, and thermogravimetric analysis. Finally, photoluminescence and magnetic studies are conducted to evaluate their potential as a functional material.

In contrast to a tungsten nitrido complex endowed with a tripodal silanolate ligand framework, which was reported in the literature to be a dimeric species with a metallacyclic core, the corresponding molybdenum nitrides 3are monomeric entities comprising a regular terminal nitride unit, as proven by single-crystal X-ray diffraction (SC-XRD). Their electronic character is largely determined by the constraints imposed on the metal center by the podand ligand architecture. 95Mo nuclear magnetic resonance (NMR) and, to a lesser extent, 14N NMR spectroscopy allow these effects to be studied, which become particularly apparent upon comparison with the spectral data of related molybdenum nitrides comprising unrestrained silanolate, alkoxide, or amide ligands. Attempted nitrogen atom transfer from these novel terminal nitrides to [(tBuArN)3Mo] (Ar = 3,5-dimethylphenyl) as the potential acceptor stopped at the stage of unsymmetric dimolybdenum µ-nitrido complex 13aas the first intermediate along the reaction pathway. SC-XRD, NMR, electron paramagnetic resonance, and ultraviolet–visible spectroscopy as well as magnetometry in combination with density functional theory allowed a clear picture of the geometric and electronic structure of this mixed-valent species to be drawn. 13ais formally best described as an adduct of the type [(Mo[O])+III–(µN)-III–(Mo[N])+VI], S= 1/2complex with (Mo[O])+IIIin the low-spin configuration, whereas related complexes such as [(AdS)3Mo–(µN)–Mo(NtBuAr)3] (19; Ad = 1-adamantyl) have previously been regarded in the literature as mixed-valent Mo+IV/Mo+Vspecies. The spin population at the two Mo centers is uneven and notably larger at the more reduced Mo[O]atom, whereas the only spin present at the (µN) bridge is derived from spin polarization.

The new compound Ba4Al7Li28.08O26.92N1.08consists of AlO4/AlO3N tetrahedra, 10-fold coordinated Ba2+cations, and a highly condensed edge- and corner-sharing LiO4tetrahedra framework, which leads to a degree of condensation greater than 1. The first barium oxonitridolithoaluminate was synthesized by a high-temperature solid-state reaction in a weld-shut tantalum ampoule and the crystal structure has been determined by single-crystal X-ray diffraction. Ba4Al7Li28.08O26.92N1.08crystallizes in the monoclinic space group P21/m(no. 11) with the lattice parameters a= 1052.41(3), b= 615.93(2), c= 1088.45(4) pm, β = 98.86(1)°, and a volume of V= 0.69712(4) nm3. In addition, Ba4Al7Li28.08O26.92N1.08doped with the activator ion Eu2+, exhibits a broad band emission with a maximum at λmax= 524 nm (2.34 eV) with a fwhm of 112 nm (4373 cm–1/0.54 eV), which can be described by a superposition of two adjusted emission bands at λmax= 515 nm (2.41 eV) with a fwhm of 70 nm (2704 cm–1/0.34 eV), and at λmax= 574 nm (2.18 eV) with a fwhm of 127 nm (4127 cm–1/0.51 eV).

The synthesis of Nb4S3, a previously undiscovered binary sulfide, was achieved using Nb3Br7S as a precursor. Its structure is composed of Nb6S triangular prisms arranged in a polar (Imm2) configuration, with sulfur atoms lying in channels along the aaxis. Electrical resistivity measurements and density functional theory calculations were used to determine that Nb4S3is metallic and therefore a polar metal, with metallic bands occupied by electrons with primarily niobium character. The electrons near the Fermi level are so closely associated with the niobium sublattice that the sulfur atoms have positive Born effective charges, indicating that the electrostatic interactions between sulfur atoms are unscreened. Calculations of the dependence of the electron density on the sulfur atomic positions confirm that the metallic electrons do not screen the dipole–dipole interactions between sulfur atoms, which allows polarity and metallicity to coexist in Nb4S3. These findings suggest that applied electric fields might be able to reverse the polarity of thin films of Nb4S3.

We report on the new monosubstituted aluminum Keggin-type germanotungstate (C4H12N)4[HAlGeW11O39(H2O)]·11H2O ([Al(H2O)GeW11]4–), which has been synthesized at room temperature via rearrangement of the dilacunary [γ-GeW10O36]8–polyoxometalate precursor. [Al(H2O)GeW11]4–has been characterized thoroughly both in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by cyclic voltammetry (CV) 183W, 27Al NMR and UV–vis spectroscopy. A study on the antibacterial properties of [Al(H2O)GeW11]4–and the known aluminum(III)-centered Keggin polyoxotungstates (Al-POTs) α-Na5[AlW12O40] (α-[AlW12O40]5–) and Na6[Al(AlOH2)W11O39] ([Al(AlOH2)W11O39]6–) revealed enhanced activity for all three Al-POTs against the Gram-negative bacterium Moraxella catarrhalis(minimum inhibitory concentration (MIC) up to 4 μg mL–1) and the Gram-positive Enterococcus faecalis(MIC up to 128 μg mL–1) compared to the inactive Al(NO3)3salt (MIC > 256 μg mL–1). CV indicates the redox activity of the Al-POTs as a dominating factor for the observed antibacterial activity with increased tendency to reduction, resulting in increased antibacterial activity of the POT.

A comprehensive and diverse benchmark set for the calculation of 29Si NMR chemical shifts is presented. The SiS146set includes 100 silicon containing compounds with 146 experimentally determined reference 29Si NMR chemical shifts measured in nine different solvents in a range from −400 to +828 ppm. Silicon atoms bound to main group elements as well as transition metals with coordination numbers of 2–6 in various bonding patterns including multiple bonds and coordinative and aromatic bonding are represented. The performance of various common and specialized density functional approximations including (meta-)GGA, hybrid, and double-hybrid functionals in combination with different AO basis sets and for differently optimized geometries is evaluated. The role of scalar-relativistic effects is further investigated by inclusion of the zeroth order regular approximation (ZORA) method into the calculations. GGA density functional approximations (DFAs) are found to outperform hybrid DFAs with B97-D3 performing best with an MAD of 7.2 ppm for the subset including only light atoms (Z< 18), while TPSSh is the best tested hybrid functional with an MAD of 10.3 ppm. For 29Si cores in the vicinity of heavier atoms, the application of ZORA proved indispensable. Inclusion of spin–orbit effects into the 29Si NMR chemical shift calculation decreases the mean absolute deviations by up to 74% compared to calculations applying effective core potentials.

CblC is a chaperone that catalyzes removal of the β-axial ligand of cobalamin (or B12), generating cob(II)alamin in an early step in the cofactor trafficking pathway. Cob(II)alamin is subsequently partitioned to support cellular needs for the synthesis of active cobalamin cofactor derivatives. In addition to the β-ligand transferase activity, the Caenorhabdiitis elegansCblC (ceCblC) and clinical R161G/Q variants of the human protein exhibit robust thiol oxidase activity, converting glutathione to glutathione disulfide while concomitantly reducing O2to H2O2. The chemical efficiency of the thiol oxidase side reaction during ceCblC-catalyzed dealkylation of alkylcobalamins is noteworthy in that it effectively scrubs ambient oxygen from the reaction mixture, leading to air stabilization of the highly reactive cob(I)alamin product. In this study, we report that the enhanced thiol oxidase activity of ceCblC requires the presence of KCl, which explains how the wasteful thiol oxidase activity is potentially curtailed inside cells where the chloride concentration is low. We have captured an unusual chlorocob(II)alamin intermediate that is formed in the presence of potassium chloride, a common component of the reaction buffer, and have characterized it by electron paramagnetic resonance, magnetic circular dichroism, and computational analyses. The ability to form a chlorocob(II)alamin intermediate could represent an evolutionary vestige in ceCblC, which is structurally related to bacterial B12-dependent reductive dehalogenases that have been proposed to form halogen cob(II)alamin intermediates in their catalytic cycle.

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(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N–N bond cleavage.

Metal oxyfluorides are currently attracting much attention for next-generation rechargeable batteries because of their high theoretical capacity and resulting high energy density. Rhombohedral VO2F is promising because it allows two-electron transfer during electrochemical lithium cycling, with a theoretical capacity of 526 mAh g–1. However, the chemical changes it undergoes during operation are not clearly understood. In this work, a combination of synchrotron X-ray and neutron diffraction was employed to accurately describe the crystal structure of both pristine and lithiated VO2F, using samples with high crystallinity to overcome challenges in previous studies. The mechanism and reversibility of the lithium insertion was monitored in real time by high angular synchrotron diffraction measurements, performed in operandoon a lithium battery in the high-voltage range: 3.9–2.3 V vs Li+/Li. Insertion of up to one lithium ion proceeds through a solid-solution reaction, while Rietveld refinements of neutron powder diffraction data revealed that the lithiated states adopt the noncentrosymmetric R3cframework, uncovering an octahedral Li–(O/F)6coordination with reasonable Li–O/F bond lengths. This work further evaluates the redox changes of VO2F upon Li intercalation. By a comparison of changes in electronic states of all the elements in the compound, it clarifies the critical role of both anions, O and F, in the charge compensation through their covalent interactions with the 3d states of V. The clear evidence of participation of F challenges existing assumptions that its high electronegativity renders this anion largely a spectator in the redox reaction.

A cyclohexyl substituent strongly prefers the chair conformation with large substituents in equatorial positions, while other cycloalkyls are structurally more flexible. In hierarchically formed dimeric titanium(IV) tris(catecholates) equatorial versus axial connection of the cyclohexane to the ester results in either a more compact (axial) or more expanded (equatorial) structure. In DMSO solution the axial position results in a compact structure which minimizes solvophobic effects, leading to higher stability. However, computational investigations indicate that additionally intramolecular London dispersion interactions significantly contribute to the stability of the dimer. Thus, weak side-chain–side-chain interactions are responsible for the high stability of cyclohexyl ester derivatives with axial compared to equatorial ester connection.