Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis,Chemical and Thermal Instability,Crystal and Magnetic Structures

The reaction of Fe(NO₃)₃⋅9 H₂O with KOH under hydroflux conditions at about 200 °C produces red crystals of K_2−xFe₄O_7−x(OH)_x in a quantitative yield. In the crystal structure, edge-sharing [FeO₆] octahedra form Fe₂O₆] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO₄] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 1m) and the hexagonal (P6₃/mcm) polytypes of K_2−xFe₄O_7−x(OH)_x show oriented intergrowth. The sub-stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K_2−xFe₄O_7−x(OH)_x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K_2−xFe₄O_7−x(OH)_x hydrolyzes and K₂CO₃ ⋅ H₂O forms gradually on the surface of the K_2−xFe₄O_7−x(OH)_x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K_2−xFe₄O_7−x(OH)_x proceeds via a topotactic transformation into K_1+x′Fe₁₁O₁₇, adopting the rhombohedral β’’ or the hexagonal β-aluminate-type structure, before γ-Fe₂O₃ is formed above 950 °C, which then converts into thermodynamically stable α-Fe₂O₃.     

A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes

The influence of ligands on the spin state of a metal ion is of central importance for bioinorganic chemistry, and the production of base‐metal catalysts for synthesis applications. Complexes derived from [Fe(bpp)₂]²⁺ (bpp=2,6‐di{pyrazol‐1‐yl}pyridine) can be high‐spin, low‐spin, or spin‐crossover (SCO) active depending on the ligand substituents. Plots of the SCO midpoint temperature (T ) in solution vs. the relevant Hammett parameter show that the low‐spin state of the complex is stabilized by electron‐withdrawing pyridyl (“X”) substituents, but also by electron‐donating pyrazolyl (“Y”) substituents. Moreover, when a subset of complexes with halogeno X or Y substituents is considered, the two sets of compounds instead show identical trends of a small reduction in T for increasing substituent electronegativity. DFT calculations reproduce these disparate trends, which arise from competing influences of pyridyl and pyrazolyl ligand substituents on Fe‐L σ and π bonding.     

Na2Ba[Na2Sn2S7]: Structural Tolerance Factor-Guided NLO Performance Improvement

The strong mutual coupling of and even the opposite change in the key parameters, such as the band gap (E_g) and second-order harmonic generation (SHG), leads to the extreme scarcity in high-performance IR nonlinear optical (NLO) chalcogenides. Herein, we report 8 new sulfides, Na₂Ba[(Ag_xNa_1−x)₂Sn₂S₇] ( 1 , x=0; 1 series , x=0.1–0.6; Na₂Ba[(Li_0.58Na_0.42)₂Sn₂S₇], 1-0.6Li ); Na₂Sr[Cu₂Sn₂S₇] ( 2 ); and Na₂Ba[Cu₂Sn₂S₇] ( 3 ). We use the structural tolerance factor ( ) to connect the chemical composition, crystal structure, and NLO properties. Guided by these correlations, a better balance between E_g and SHG is realized in 1 , which exhibits a large E_g of 3.42 eV and excellent NLO properties (SHG: 1.5×AGS; laser-induced damage threshold: 12×AGS), representing the best performance among the known Hg- or As-free sulfides to date.     

Inorganic Solid-State Nonlinear Optical Switch with a Linearly Tunable Tc Spanning a Wide Temperature Range

Nonlinear optical (NLO) switch materials that turn on/off second-harmonic generation (SHG) at a phase transition temperature (T_c) are promising for applications in the fields of photoswitching and optical computing. However, precise control of T_c remains challenging, mainly because a linearly tunable T_c has not been reported to date. Herein, we report a unique selenate, tetragonal P 2₁c [Ag(NH₃)₂]₂SeO₄ with a=b=8.5569(2) Å and c=6.5208(2) Å that exhibits a strong SHG intensity (1.3×KDP) and a large birefringence (Δn_obv.=0.08). This compound forms a series of isostructural solid-solution crystals [Ag(NH₃)₂]₂S_xSe_1−xO₄ (x=0–1.00) that exhibit excellent NLO switching performance and an unprecedented linearly tunable spanning 430 to 356 K. The breaking of localized hydrogen bonds between SeO₄²⁻ and the cation triggers a phase transition accompanied by hydrogen bond length changes with increasing x and a linear change in the enthalpy .     

Bioluminescent Enzymatic Assay as a Tool for Studying Antioxidant Activity and Toxicity of Bioactive Compounds

A bioluminescent assay based on a system of coupled enzymatic reactions catalyzed by bacterial luciferase and NADH:FMN‐oxidoreductase was developed to monitor toxicity and antioxidant activity of bioactive compounds. The assay enables studying toxic effects at the level of biomolecules and physicochemical processes, as well as determining the toxicity of general and oxidative types. Toxic and detoxifying effects of bioactive compounds were studied. Fullerenols, perspective pharmaceutical agents, nanosized particles, water‐soluble polyhydroxylated fullerene‐60 derivatives were chosen as bioactive compounds. Two homologous fullerenols with different number and type of substituents, C₆₀O_2–4(OH)_20–24 and Fe_0.5C₆₀(OH) _xO_y (x + y = 40–42), were used. They suppressed bioluminescent intensity at concentrations >0.01 g L^?1 and >0.001 g L^?1 for C₆₀O_2–4(OH)_20‐24 and Fe_0.5C₆₀(OH)_xO_y, respectively; hence, a lower toxicity of C₆₀O_2–4(OH)_20–24 was demonstrated. Antioxidant activity of fullerenols was studied in model solutions of organic and inorganic oxidizers; changes in toxicities of general and oxidative type were determined; detoxification coefficients were calculated. Fullerenol C₆₀O_2–4(OH)_20–24 revealed higher antioxidant ability at concentrations 10^?17?10^?5 g L^?1. The difference in the toxicity and antioxidant activity of fullerenols was explained through their electron donor/acceptor properties and different catalytic activity. Principles of bioluminescent enzyme assay application for evaluating the toxic effect and antioxidant activity of bioactive compounds were summarized and the procedure steps were described.     

Hole and Electron Doping of the 4d Transition‐Metal Oxyhydride LaSr3NiRuO4H4

Hole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion‐exchange) is extremely challenging as these low‐temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition‐metal oxyhydride LaSr₃NiRuO₄H₄ by first preparing precursors in the range La_xSr_4?xNiRuO₈ 0.5<x<1.4 and then converting into the corresponding La_xSr_4?xNiRuO₄H₄ phases. This is particularly noteworthy as the (Ni/Ru)H₂ sheets in the La_xSr_4?xNiRuO₄H₄ phases are structurally analogous to the CuO₂ sheets in cuprate superconductors and hole doping (Ni^1+/2+, Ru²⁺) or electron doping (Ni²⁺, Ru^1+/2+) yields materials with partial occupancy in Ni/Ru –H 1s bands which are analogous to the partially occupied Cu –O 2p bands present in the CuO₂ sheets of doped superconducting cuprates.     

Potassium Ion Conductivity in the Cubic Labyrinth of a Piezoelectric,Antiferromagnetic Oxoferrate(III) Tellurate(VI)

Orange-colored crystals of the oxoferrate tellurate K_12+6xFe₆Te_4−xO₂₇ [x=0.222(4)] were synthesized in a potassium hydroxide hydroflux with a molar water–base ratio n(H₂O)/n(KOH) of 1.5 starting from Fe(NO₃)₃ ⋅ 9H₂O, TeO₂ and H₂O₂ at about 200 °C. By using (NH₄)₂TeO₄ instead of TeO₂, a fine powder consisting of microcrystalline spheres of K_12+6xFe₆Te_4−xO₂₇ was obtained. K_12+6xFe₆Te_4−xO₂₇ crystallizes in the acentric cubic space group I 3d. [Fe^IIIO₅] pyramids share their apical atoms in [Fe₂O₉] groups and two of their edges with [Te^VIO₆] octahedra to form an open framework that consists of two loosely connected, but not interpenetrating, chiral networks. The flexibility of the hinged oxometalate network manifests in a piezoelectric response similar to that of LiNbO₃.The potassium cations are mobile in channels that run along the <111> directions and cross in cavities acting as nodes. The ion conductivity of cold-pressed pellets of ball-milled K_12+6xFe₆Te_4−xO₂₇ is 2.3×10⁻⁴ S ⋅ cm⁻¹ at room temperature. Magnetization measurements and neutron diffraction indicate antiferromagnetic coupling in the [Fe₂O₉] groups.     

LaSr3NiRuO4H4: A 4d Transition‐Metal Oxide–Hydride Containing Metal Hydride Sheets

The synthesis of the first 4d transition metal oxide–hydride, LaSr₃NiRuO₄H₄, is prepared via topochemical anion exchange. Neutron diffraction data show that the hydride ions occupy the equatorial anion sites in the host lattice and as a result the Ru and Ni cations are located in a plane containing only hydride ligands, a unique structural feature with obvious parallels to the CuO₂ sheets present in the superconducting cuprates. DFT calculations confirm the presence of S= Ni⁺ and S=0, Ru²⁺ centers, but neutron diffraction and μSR data show no evidence for long‐range magnetic order between the Ni centers down to 1.8 K. The observed weak inter‐cation magnetic coupling can be attributed to poor overlap between Ni 3d and H 1s in the super‐exchange pathways.     

The conditions of formation and physicochemical properties of Nd1 ? xBaxMn1 ? yFeyO3 phases

The homogeneity regions of Nd_{1 − x} Ba _x MnO₃ (0.0 ≤ x ≤ 0.25) and NdMn_{1 − y} Fe _y O₃ (0.0 ≤ y ≤ 1.0) orthorhombic solid solutions in air at 1373 K were determined. The region of the existence of Nd_{1 − x} Ba _x Mn_{1 − y} Fe _y O₃ orthorhombic solid solutions in air at 1373 K was studied. A fragment of the phase diagram of the NdMnO₃-BaMnO₃-BaFeO_2.5-NdFeO₃ quasi-quaternary complex oxide system in air at 1373 K was suggested. The mechanothermal properties of Nd_0.75Ba_0.25MnO₃, Nd_0.8Ba_0.2Mn_0.9Fe_0.1O₃, Nd_0.8Ba_0.2Mn_0.7Fe_0.3O₃, and Nd_0.8Ba_0.2Mn_0.5Fe_0.5O₃ doped neodymium manganates were studied.     

Nickel‐Catalyzed Stereospecific C−H Coupling of Benzamides with Epoxides

A Ni(OAc)₂‐catalyzed C?H coupling of 8‐aminoquinoline‐derived benzamides with epoxides has been developed. The reaction proceeds with concomitant removal of the 8‐aminoquinoline auxiliary to form the corresponding 3,4‐dihydroisocoumarins directly. Additionally, the nickel catalysis is stereospecific, and the cis‐ and trans‐epoxides are converted into the corresponding cis‐ and trans‐dihydroisocoumarins with retention of configuration, which is complementary to previously reported palladium catalysis. Moreover, while still preliminary, the C ?H functionalization is also achieved in the presence of modified NiCl₂ catalysts.     

A Long Cycle‐Life High‐Voltage Spinel Lithium‐Ion Battery Electrode Achieved by Site‐Selective Doping

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode candidate for the next‐generation high energy‐density lithium‐ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site‐selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd m structure. This site‐selective doping not only suppresses unfavorable two‐phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg‐doped LNMOs exhibit extraordinarily stable electrochemical performance in both half‐cells and prototype full‐batteries with novel TiNb₂O₇ counter‐electrodes. This work pioneers an atomic‐doping engineering strategy for electrode materials that could be extended to other energy materials to create high‐performance devices.     

Blue‐Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons

Room‐temperature luminescent Co^III complexes ( 1 and 2 ) are presented that exhibit intense ligand‐to‐metal and ligand‐to‐ligand charge transfer absorption in the low‐energy UV region (λ_abs≈360–400 nm) and low‐negative quasi‐reversible reduction events (E^1/2_(red)=?0.58 V and ?0.39 V vs. SCE for 1 and 2 , respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong σ‐donation of the ligands, the combined effect of which helps to separate the emissive ³LMCT (triplet ligand‐to‐metal charge transfer) and the non‐emissive ³MC (triplet metal‐centered) states. 1 and 2 were found to be powerful photo‐oxidants (E =2.26 V and 2.75 V vs. SCE of 1 and 2 , respectively) and were used as inexpensive photoredox catalysts for the regioselective mono(trifluoromethylation) of polycyclic aromatic hydrocarbons (PAHs) in good yields (ca. 40–58 %).     

Antiferromagnetic Alkali Metal Oxohydroxoferrates(III) with Correlated Hydrogen Bonding Systems

The oxohydroxoferrates(III) A₂[Fe₂O₃(OH)₂] (A=K, Rb, Cs) were synthesized under hydroflux conditions. Approximately equimolar mixtures of the alkali metal hydroxides and water were reacted with Fe(NO₃)₃ ⋅ 9H₂O at about 200 °C. The product formation depends on the hydroxide concentration, therefore also other reaction products, such as KFeO₂, K_2−x[Fe₄O_7−x(OH)_x] or α-Fe₂O₃, are obtained. The crystal structures of the oxohydroxoferrates(III) A₂[Fe₂O₃(OH)₂] follow the same structural principle, yet differ in their layer stacking or/and their hydrogen bonding systems depending on A and temperature. In the resulting four different orthorhombic structure types, [FeO₃OH]⁴⁻ tetrahedra share their oxide corners to create folded Fe₂O₃(OH)₂]²⁻ layers. The terminal hydroxide ligands form hydrogen bonds between and/or within the layers. The positions of the hydrogen atoms in these networks are correlated. The A⁺ cations are located between the folded anionic layers as well as in their trenches. Under reaction conditions, the potassium compound crystallizes in the space group Cmce (Pearson symbol oC88), showing a bimodal disorder of the hydrogen atoms in hydrogen bridges. In a virtually hysteresis-less first-order transition at 340(2) K, the structure slightly distorts into the room-temperature modification with the subgroup Pbca (oP88), and the hydrogen atoms order. The rubidium and caesium compounds are isostructural to each other but not to the potassium compound, and are always obtained as mixtures of two modifications with space groups Cmce (oC88′) and Immb (oI88). Upon heating, the oxohydroxoferrates decompose into their anhydrides AFeO₂ and water. The type of hydrogen bonding network influences the decomposition temperature, the structure and the morphology of the crystals. Despite the presence of iron(III), which was confirmed by ⁵⁷Fe-Mössbauer spectroscopy, K₂[Fe₂O₃(OH)₂] is diamagnetic in the investigated temperature range between 1.8 and 300 K. Neutron diffraction revealed strong antiferromagnetic coupling of the magnetic moments, which are inverted in neighboring tetrahedra.     

Water Formation under Silica Thin Films: Real‐Time Observation of a Chemical Reaction in a Physically Confined Space

Using low‐energy electron microscopy and local photoelectron spectroscopy, water formation from adsorbed O and H₂ on a Ru(0001) surface covered with a vitreous SiO₂ bilayer (BL) was investigated and compared to the same reaction on bare Ru(0001). In both cases the reaction is characterized by moving reaction fronts. The reason for this might be related to the requirement of site release by O adatoms for further H₂‐dissociative adsorption. Apparent activation energies ( ) are found for the front motion of 0.59 eV without cover and 0.27 eV under cover. We suggest that the smaller activation energy but higher reaction temperature for the reaction on the SiO₂ BL covered Ru(0001) surface is due to a change of the rate‐determining step. Other possible effects of the cover are discussed. Our results give the first values for in confined space.     

Double‐Gyroid Nanostructure Formation by Aggregation‐Induced Atropisomerization and Co‐Assembly of Ionic Liquid‐Crystalline Amphiphiles

We report a new molecular‐design principle for creating double‐gyroid nanostructured molecular assemblies based on atropisomerization. Ionic amphiphiles containing two imidazolium rings close to each other were designed and synthesized. NMR data revealed that the rotation of the imidazolium rings is restricted, with an activation energy as high as 63 kJ mol^?1 in DMSO‐d₆ solution (DFT prediction for a model compound in the vacuum: 90–100 kJ mol^?1). Due to the restricted rotation, the amphiphiles feature “double” atropisomeric axes in their ionic segments and form three stable atropisomers: meso, R, and S. These isomers co‐organize into ‐type bicontinuous cubic liquid‐crystalline mesophases through nanosegregation of the ionic and non‐ionic parts. Considering the intrinsic characteristic of ‐type bicontinuous cubic structures that they are composed of intertwined right‐ and left‐handed single gyroids, we propose that the simultaneous presence of both R‐ and S‐atropisomers is an important contributor to the formation of double‐gyroid structures.     

Entropic Contributions to Sodium Solvation and Solvent Stabilization upon Electrochemical Sodium Deposition from Diglyme and Propylene Carbonate Electrolytes

The formation of an appropriate solid electrolyte interphase (SEI) at the anode of a sodium battery is crucially dependent on the electrochemical stability of solvent and electrolyte at the redox potential of Na/Na⁺ in the respective system. In order to determine entropic contributions to the relative stability of the electrolyte solution, we measure the reaction entropy of Na metal deposition for diglyme (DG) and propylene carbonate (PC) based electrolyte solutions by electrochemical microcalorimetry at single electrodes. We found a large positive reaction entropy for Na⁺ deposition in DG of Δ_R 234 J mol⁻¹ K⁻¹ (c.f.: Δ_R 83 J mol⁻¹ K⁻¹), which signals substantial entropic destabilization of Na⁺ in DG by about 0.73 eV, thus increasing the stability of solvent and electrolyte relative to Na⁺ reduction. We attribute this strong entropic destabilization to a highly negative solvation entropy of Na⁺, due to the low dielectric constant and high freezing entropy of DG.     

Fused Perovskite Tunnel Structures in Ba5Fe6+xS4+xO8 (0.44≤x≤0.55) with x‐Dependent Two‐Stage Magnetizations

Ba₅Fe_6+xS_4+xO₈ was synthesized through a solid‐state reaction, and pure powders of nominal compositions x=0.44–0.55 were obtained after being rinsed with water. The crystal structures (P4/mmm, a=10.13, c=4.03 Å) and sample purities were investigated by powder synchrotron X‐ray diffraction and were found to be composed of a tunnel lattice (Ba₅Fe₆S₄O₈), built from fused perovskite units and the tunnel filling (Fe_xS_x). The variable composition, that is, the tunnel filling (x), causes partially occupied sites as well as crystallographic split positions. Ba₅Fe_6+xS_4+xO₈ (x=0.525) is semiconducting and all investigated compositions exhibit magnetic ground states that could be described as either semi‐spin‐glass‐like (x>0.5) or canted antiferromagnetic (x<0.5). The spin‐glass in x=0.525 exhibits magnetic relaxations that are affected by ageing.     

Isolation of a Perfectly Linear Uranium(II) Metallocene

Reduction of the uranium(III) metallocene [(η⁵‐C₅ⁱPr₅)₂UI] ( 1 ) with potassium graphite produces the “second‐generation” uranocene [(η⁵‐C₅ⁱPr₅)₂U] ( 2 ), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f³ 6d¹. Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2 , including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.     

A Square‐Planar Complex of Platinum(0)

The Pt⁰ complex [Pt(PPh₃)(Eind₂‐BPEP)] with a pyridine‐based PNP‐pincer‐type phosphaalkene ligand (Eind₂‐BPEP) has a highly planar geometry around Pt with ∑(Pt)=358.6°. This coordination geometry is very uncommon for formal d¹⁰ complexes, and the Pd and Ni homologues with the same ligands adopt distorted tetrahedral geometries. DFT calculations reveal that both the Pt and Pd complexes are M⁰ species with nearly ten valence electrons on the metals whereas their atomic orbital occupancies are evidently different from one another. The Pt complex has a higher occupancy of the atomic 6s orbital because of strong s–d hybridization due to relativistic effects, thereby adopting a highly planar geometry reflecting the shape and orientation of the partially unoccupied orbital.     

Kinetics of the Antibody Recognition Site in the Third IgG‐Binding Domain of Protein G

Protein dynamics occurring on a wide range of timescales play a crucial role in governing protein function. Particularly, motions between the globular rotational correlation time ( ) and 40 μs (supra‐ window), strongly influence molecular recognition. This supra‐ window was previously hidden, owing to a lack of experimental methods. Recently, we have developed a high‐power relaxation dispersion (RD) experiment for measuring kinetics as fast as 4 μs. For the first time, this method, performed under super‐cooled conditions, enabled us to detect a global motion in the first β‐turn of the third IgG‐binding domain of protein G (GB3), which was extrapolated to 371±115 ns at 310 K. Furthermore, the same residues show the plasticity in the model‐free residual dipolar coupling (RDC) order parameters and in an ensemble encoding the supra‐ dynamics. This β‐turn is involved in antibody binding, exhibiting the potential link of the observed supra‐ motion with molecular recognition.