We design a kinetically-controlled regime of colloidal synthesis to enable the formation of the metastable phase. 1T’ WSe2 branched few-layered nanosheets are produced in high yield and in a reproducible and controlled manner. The 1T’ phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 °C. The 1T’ WSe2 nanosheets demonstrate a metallic nature exhibited by an enhanced electrocatalytic activity for hydrogen evolution reaction as compared to the 2H WSe2 nanosheets and comparable to other 1T’ phases. This synthesis design can potentially be extended to different materials providing direct access of metastable phases.Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. Access to metastable crystal phases is limited as their direct synthesis is challenging, restricting the spectrum of reachable materials. Here, we demonstrate the solution phase synthesis of the metastable distorted octahedrally coordinated structure (1T’ phase) of WSe 1T’ phases of transition metal dichalcogenides show promise for electrocatalysis, energy storage, and spintronic applications but are difficult to obtain. Here the authors synthesize 1T’ WSe2 few-layered nanosheets by kinetically-controlled colloidal synthesis, and test their electrocatalytic activity. The versatility of properties of TMDs is enabled by the polymorphism of their monolayers, where metal coordination changes from trigonal prismatic (2H phase) to octahedral (1T phase) and distorted octahedral (1T’ phase).Atomically thin transition metal dichalcogenides (TMDs) have been attracting enormous attention in the past decades as promising materials for a variety of disparate applications ranging from flexible electronics7 due to their metallic nature8. Moreover, 1T’ WSe2 single layer is predicted to be a large gap quantum spin Hall (QSH) insulator suitable for application in spintronic devices9 both operable at ambient temperature in contrast to the 1T’ WTe210 and benefiting from chemical stability of the material compared to that of other currently known large gap QSH insulators such as stanene11 and two-dimensional In-Sb compounds12 existing in an inert atmosphere only.The 1T and 1T’ phases of group VI TMDs started to emerge only recently; however, compared to the semiconducting 2H phase, they have exhibited an exceptional performance for electrocatalytic hydrogen evolution and energy storage applications owing to the dramatically reduced charge transfer resistance2, MoSe2, WS2 and WSe2), direct synthesis of these materials generally leads to formation of the thermodynamically stable 2H phase14 with a few recent exceptions of wet-chemical synthesis of the WS2 nanodisks15 and WS2 nanoribbons16 with the distorted 1T structure, however, stabilised by the charged precursor residues intercalated between the layers. This metastable 1T’ phase converts into the thermodynamically stable 2H phase once the charges are removed. The direct synthesis of the metastable 1T’ phase of high crystal quality and not stabilised by foreign species17 is challenging and has only been recently reported for bulk MoS2 and MoSe2 crystals18.Owing to the metastable nature of the 1T and 1T’phases of group VI sulphides and selenides 20 or doping beyond degenerate level21 or applied mechanical strain22. While for MoS2 and WS2 the 1T’ phase has been reported via these treatments, there is no current evidence that electron transfer can convert the 2H phase of WSe2 into the 1T’. Indeed, intercalation studies with organolithium treatment followed by exfoliation show evidence of persistency of 2H WSe223. Atomically thin WSe2 nanosheets prepared via wet chemical approaches or vapour deposition techniques reported so far acquired the thermodynamically stable 2H phase25 with the only exception of molecular beam epitaxy deposition, which led to the formation of nanometre-sized 1T’ WSe2 single layers9. Overall, there are no reported established methods to achieve 1T’ WSe2 over large areas or measurable quantities, although energy difference between 1H and 1T’ phases of WSe2 is only 0.27 eV per formula unit that suggests that the metastable 1T’ can be obtained under certain reaction conditions26.The 1T/1T’ phases are more commonly obtained via distortion of the 2H phase as a result of either electrical gating2 not stabilised by charged species. We design a kinetically controlled regime of colloidal synthesis to enable nucleation and growth of 1T’ WSe2 branched few-layered nanosheets with high yield and in a reproducible manner. We report a full study of the atomic structure (high-resolution transmission electron microscopy (HR TEM)), the Raman characteristic peaks, chemical bonding (X-ray photoelectron spectroscopy (XPS)) and layer stacking order (powder X-ray diffraction (XRD)) proving the 1T’ nature of WSe2. We also found that the 1T’ phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 °C. The 1T’ WSe2 nanosheets demonstrate an enhanced electrocatalytic performance for hydrogen reduction as compared to the 2H WSe2 as expected for the metallic phases.Here we demonstrate a direct solution-phase synthesis of the metastable distorted octahedral structure (1T’ phase) of WSe2 nanosheets were synthesised through a solution-phase reaction between tungsten hexacarbonyl and trioctylphosphine selenide (TOP:Se) complex in hot oleic acid (OlAc) as described in the Methods section. TEM images shown in Fig. 2 forms well-defined flower-like nanostructures with an average diameter of 200 nm. The nanoflowers are made of multiple petals emerging from a central core region. In annular dark-field scanning transmission electron microscopy (ADF STEM) images, petal edges appear curled and ultra-thin in nature, while side view TEM images clearly demonstrate that the petals are thinning down to single layer towards the rims  presumably due to the scrolling of flexible ultra-thin petals along the [010] direction perpendicular to the petal rim , when the monomer adsorption rate exceeds the dissolution rate and a kinetically driven growth of the metastable phase nuclei is favoured28. At high monomer concentration, nuclei critical size is notoriously small, and we cannot exclude that stable clusters of both 1T’ and 2H ‘phases’ may nucleate in solution. Second, zigzag chains running along [010] direction of the 1T’ phase are likely to propagate faster29, so out of two possibly competing reactions growth of the 1T’ phase along the [010] direction might be favourable over 2H as it may minimize the total surface energy.In contrast to a chemical vapour deposition (CVD) growth that occurs in a diffusion-mediated regime6 to more active WCl6) precursor reactivity and additional activation of tungsten precursor by complexing with additives (hexamethyldisilazane and tetradecylphosphonic acid) consistently led to the formation of the metastable 1T’ phase and to negligible changes in the morphology. The least active tungsten carbonyl and the most active elemental selenium yield the highest-quality WSe2 nanoflowers. Furthermore, crystallisation in the metastable 1T’ phase with metal chains running through the structure can potentially explain the formation of branched structures themselves. Branched morphology has been reported for the 1T’ ReS2 nanosheets where distortion in the metal sublattice was suggested to facilitate adsorption of Re atom at the Re-Re metal bond leaving highly reactive under-coordinated chalcogen atom that served as a nucleation site for the growth in the direction perpendicular to the surface of 1T’ ReS2 nanosheet30.Synthesis temperature reported here was kept not >300 °C as higher temperatures would lead to solvent boiling and lower temperatures would inhibit any nucleation and growth to occur. The fact that high supersaturation at synthesis temperature plays a key role in determining the formation of 1T’ phase is supported by the evidence that the phase obtained is unaffected by the use of different precursors of tungsten and selenium, by changing coordinating solvent or the synthesis time (between 3 and 15 h) as summarised in Supplementary Figs. 2 nanoflowers form stable suspensions in ethanol  was found to be significantly shifted from the reported positions of the 2H WSe2 and was assigned to the 1T’ phase. Similar shifts to lower binding energies have been reported for the 1T phase of MoS2 and MoSe2 that was produced upon n-butyllithium treatment of the CVD-grown 2H polycrystalline films20. The shift to the lower binding energies can be attributed to the change in the metal coordination and to a slight increase of the W-Se bond lengths from 2.531 Å in the 2H phase to 2.66 Å calculated for the 1T’ phase. Minor fraction of the 2H phase (32.22 and 34.30 eV) and traces of oxidized tungsten (35.74 and 37.92 eV) are also present. Thermal annealing at 400 °C in argon atmosphere led to a complete conversion of the 1T’ phase into the hexagonal 2H phase with the 4f W+4 peaks found at 32.40 and 34.58 eV, while the lower energy 1T’ 4f W+4 doublet was nearly absent (<2 at.%). A minor increase of the oxide content occurs during the thermal annealing as indicated by an increase in intensity of the 4f W+6 doublet (<25 at. %). Similarly, two types of Se−2 atoms are found in the as-produced WSe2 nanoflowers ) absorption spectroscopy. Prior to the XPS experiments, as-produced WSeers Fig. . Broad u2 belongs to either orthorhombic or monoclinic syngony depending on the stacking order of the octahedrally coordinated monolayers as reported for the Td (1T’) WTe231 and MoTe232 (space group Pnm21) or the 1T’ MoTe233 (space group P21/m), respectively. The experimental XRD pattern of the as-produced WSe2 is shown in Fig. 2 nanoflowers, whereas presence of strong (002) reflections suggests that the bulk of WSe2 nanoflowers is a few-layered material. However, the overall symmetry differs significantly from that of the annealed WSe2 nanoflowers acquiring the 2H phase and demonstrating (100) and (103) reflections becoming prominent; their positions are in a good agreement with the standard reference positions of the bulk WSe2 (JCPDS 38–1388). Reference diffraction patterns of the 1T’ phase of WSe2 were simulated as described in the Methods section and are presented in Fig. l) reflections are allowed in the monoclinic phase, whereas only (00l) where l = 2n reflections are allowed in the orthorhombic phase. We suggest that a broad reflection found at 7 degrees 2θ in the experimental small-angle diffraction pattern of the as-produced WSe2  study was carried out , carbon foil (CF) and gold foil  imaging of the 1T’ WSe2 formed on carbon paper . Electrochemical measurements were performed in a standard three-electrode cell configuration in 1 M H2SO4 electrolyte. Polarisation curves of bare CP and CP covered with the 1T’ or 2H WSe2 nanosheets are shown in Fig. 2 nanosheets demonstrated a good catalytic activity with an overpotential of 510 mV at a benchmarking current density of −10 mA cm−2 and a Tafel slope of 150 mV dec−1 outperforming the semiconducting 2H counterpart . We should remark that the mass loading of active material has a direct impact on the current density at the working electrode and, as a consequence, on the measured overpotential at the benchmarking current density commonly used as a catalyst performance metrics37. Therefore, considerable improvements in performance for HER are possible to demonstrate at higher catalyst loadings. In order to prove this, we deposited the 1T’ WSe2 nanosheets via drop casting to obtain a higher mass loading of 250 μg cm−2, which is closer to a typical mass loading reported in literature. We could thus demonstrate −10 mA cm−2 current density achieved at only 300 mV overpotential  conducted on the as-produced (1T’) and annealed (2H) WSeSe2 Fig. . Further2 nanosheets reported here is comparable to that of chemically exfoliated MoS2 and WS2 (1T phases)38 and better than that of exfoliated 2H MoS2 and WSe239 and synthesised 2H WS240, MoSe241 and WSe242 nanosheets , selenium , trioctylphosphine , OlAc , acetone , and ethanol  were used as received without further purification. In all, 1 M trioctylphosphine selenide (TOP:Se) stock solution was prepared by dissolving 5 mmol of selenium powder in 5 ml of TOP at room temperature under a nitrogen flow.Tungsten carbonyl (W(CO)2 nanosheets were precipitated by centrifugation at 5000 rpm for 10 min and washed several times with acetone. Black precipitate was finally redispersed in 5 mL of ethanol. In order to grow 1T’ WSe2 nanosheets on arbitrary conductive substrate, a piece of either CP, CF or Au foil (4 cm2) was placed in the flask prior to selenium precursor injection.In all, 0.06 mmol (20 mg) of tungsten carbonyl was placed into a three-neck flask containing 8 mL of OlAc degassed prior to the synthesis. The mixture was heated to 200 °C under vacuum and held at this temperature until complete dissolution of tungsten carbonyl precursor. After a clear pale-yellow solution was formed, the flask was flushed with dry nitrogen and the reaction mixture was heated to 300 °C. Once the temperature was reached, 0.2 mL of 1 M TOP:Se solution was swiftly injected into the reaction mixture initiating nanosheet growth and left for 3 h. Finally, the reaction was quenched by rapid cooling to room temperature, and WSe2 nanoflowers were drop-cast on Si/SiO2 substrates and then annealed in a tube furnace at 400 °C for 2 h in argon atmosphere (0.45 mbar). Annealed WSe2 nanoflowers were then redispersed in ethanol.As-produced 1T’ WSeSamples for TEM analysis were prepared on carbon-coated copper grids. Preliminary low-magnification TEM imaging was performed using a JEOL JEM-2100Plus microscope. HR TEM images and ADF STEM images were acquired on a JEOL JEM-2100F microscope with a field-emission gun operated at 200 kV accelerating voltage.SEM imaging and elemental analysis were performed using a Zeiss LEO Gemini 1525 field emission scanning electron microscope equipped with an Oxford x-act PentaFET Precision EDS detector. Images were acquired at 5 kV accelerating voltage at working distances <10 mm, while EDS maps were obtained at 20 kV.+ spectrometer equipped with a monochromated micro-focused Al Kα X-ray source. The measurements were performed at room temperature using a 20 eV energy pass with energy step of 0.1 eV. Binding energies were calibrated using a C 1s peak at 284.6 eV. XPS spectra were analysed using the Avantage software package.Measurements were performed on a Thermo Fisher K-Alpha2 nanosheets were drop-cast on Si/SiO2 substrates. X-ray diffractograms were acquired on a Bruker D2 Phaser diffractometer equipped with the Cu source and operating in the reflection scan geometry. Diffraction patterns were collected in the range 6–50 degrees 2θ with a step size of 0.026 degrees. Small-angle XRD was performed on a PANlytical X’PERT-PRO X-ray diffractometer (Cu Kα source) in the range 3–20 degrees 2θ with a step size of 0.03 degrees. Crystal structures and reference diffraction patterns of the 1T’ phase of WSe2 were simulated in the CrystalMaker and CrystalDiffract software packages based on either orthorhombic WTe2 (space group Pnm21) or monoclinic MoTe2 (space group P21/m), cell parameters a = 5.76 Å and b = 3.30 Å were estimated from the results of HR TEM and c parameter was adjusted to fit (002) peak in the experimental diffractogram and found to be approximately 12.9 Å.Concentrated suspensions of 1T’ WSe−1 grating. Laser power was kept under 0.195 mW (1%) to avoid damage to the sample.Raman spectra were recorded using a Renishaw inVia Qontor confocal Raman microscope at excitation wavelength of 532 nm using an 1800 lines mmOptical spectroscopy was performed using a PerkinElmer Lambda 25 UV-vis spectrometer in 1 cm path quartz cuvettes. Absorption spectra were recorded between 1100 and 200 nm with 1 nm spectral resolution.2 scan size, 256 points per line and a scan rate of 1 Hz. Higher-resolution scans were performed with 1024 points per line and scan rate of 1 Hz. Contact potential difference between the sample and the KPFM tip can be calculated using the equation e is the electron charge. Samples for KPFM were prepared on p-doped Si wafers; p-Si was used as a reference. Work function of WSe2ϕWse2 was calculated with respect to the work function of p-doped Si ϕSi following the equation Atomic force microscopy and KPFM were performed using an Asylum MFP-3d microscope equipped with a PtIr-coated Silicon probe (Bruker SCM-PIT-V2). Typical initial scan parameters were 16 μm−1.DSC was conducted using a Mettler Toledo DSC 3 calorimeter in nitrogen atmosphere in the temperature range 50–450 °C at heating rate of 20° min3 solution and then diluted to analytical concentrations in Milli-Q water.Qualitative elemental analysis was carried out on a Thermo Scientific iCAP 6000 Series spectrometer. Samples for ICP ES were digested in a 45% HNO2SO4  solution in Milli-Q water was chosen as electrolyte. Geometric active area of working electrodes varied from 0.25 to 0.3 cm2. All potentials were applied vs Ag/AgCl (3 M KCl) reference electrode and were converted to vs Reversible Hydrogen Electrode (RHE) following the equation V(vs RHE) = V(vsAg/AgCl) + 0.059 × pH + 0.21. Polarisation curves were recorded in the range from 0 to −0.8 V vs reference electrode at a scan rate 5 mV s−1. EIS was performed at a bias potential of −0.5 V vs Ag/AgCl (3 M KCl) while sweeping the frequency from 1 MHz to 10 mHz with an amplitude of 20 mV. The EIS data were fitted to a Randles equivalent circuit.EC testing was performed in a standard three-electrode cell configuration with a carbon foil  counter electrode and a commercial Ag/AgCl (3 M KCl) reference electrode . In all, 1 M HSupplementary Information


The Co3O4/RGO nanocomposites displayed good electrochemical behavior as anodic materials for li-ion batteries when compared to pure Co3O4. The Co3O4/RGO nanocomposites with low RGO content resulted in stable electrochemical performance with 100% coulombic efficiency at a high current density of 500 mA/g for 50 cycles. The enhanced capacity of the Co3O4/RGO nanocomposites is due to the incorporation of RGO, which resulted in a four times larger surface area than that of Co3O4. This increased surface area could facilitate the absorption of more lithium ions, resulting in excellent electrochemical performance. Interestingly, the novelty of this work is that the designed li-ion batteries showed stable electrochemical performance even at a high temperature of 100 °C, which might be useful for rechargeable battery applications in a wide temperature range.We report a microwave irradiation method for the preparation of reduced graphene oxide (RGO) based Co There is an urgent need to improve these batteries to meet energy demand requirements2. One method to enhance li-ion batteries perfomance is to design alternative negative or anode materials, including transition metal oxides, and replace the conventional anode material, graphite, which has a theoretical capacity of only 372 mAh/g3.Lithium-ion batteries have a number of applications as energy storage units mainly in electric vehicles and electronic devices owing to their high capacity, long cycling life, and environmental friendliness4 because of their superior theoretical capacity, with approximately three times the capacity of the commercial graphite that have a capacity of 372 mAh/g, making these materials good candidates for energy storage systems. Among the transition metal oxides, Co3O4 is the most frequently used as anode materials because of its high theoretical capacity (890 mAh/g)5.Currently, transition metal oxides have received considerable attention as anodic materials for use in li-ion batteries2O3) and Cobalt  oxide (Co3O4), have been widely explored for applications in li-ion batteries. However, Co3O4 is synthesized more easily than the other two, as it can be prepared from different cobalt salts by heating in air at 300 to 400 °C6. However, one limitation of Co3O4 nanoparticles as anodic material for li-ion batteries is that they experience poor cycling stability and irreversible capacity loss due to the volume expansion/contraction and agglomeration of the Co3O4 nanoparticles9.Generally, cobalt oxides, that include binary oxides such as Cobalt (II) oxide (CoO), Cobalt (III) oxide  was used to determine the thermal stability of the materials from ambient to 500 °C at a heating rate of 5 °C/min under nitrogen atmosphere. A transmission electron microscopy  was used to study the morphology of the materials. The Brunauer–Emmett–Teller (BET) was used to obtain the specific surface area through a surface area analyzer (Micromeritics ASAP 2020) by N2 adsorption-desorption while the pore size distribution was determined by the Barrett–Joyner–Halenda (BJH) method.The chemical compositions of the samples were determined using Fourier transform infrared spectroscopy  recorded in the range of 4000–400 cm6 was used as the electrolyte and lithium as the counter electrode which were then assembled into CR2032 coin-type cells in an argon-filled glove box. Charge/discharge measurements, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were all studied using an electrochemical workstation (Gamry 3000). CV was performed in the voltage window from 0 to 3 V at 50 mV/s scan rate. EIS was performed by using a sine wave of 10 mV in a frequency range of 1 Hz –100 kHz. Galvanostatic charge/discharge tests were evaluated in the voltage window from 0 to 3 V. For high temperature testing; the cell was kept inside a bomb calorimeter vessel by connecting the positive and negative terminal of the coin cell battery to the two electrodes of the vessel. The cell was then left inside the vessel at the specified testing temperature for several hours to reach thermal equilibrium. The measurements were performed at 100 °C and were tested by the Gamry potentiostat/galvanostat connected to the bomb calorimeter vessel. The batteries were cycled in a range of 0 and 3 V at 500 mA/g for 50 cycles. CV was also performed in the potential window from 0 to 3 V and at a scan rate of 50 mV/s. EIS was conducted at a frequency range of 1 Hz – 100 kHz by using a sine wave of 10 mV.To fabricate the working electrode, the active material (80%) was mixed with a conductive agent carbon black (10%) and a binding agent polyvinylidene fluoride (PVDF) (10%) in 50:50 ethanol:dimethylsulfoxide (DMSO) to form a homogenous slurry followed by casting them onto copper substrates and drying at 80 °C under vacuum to remove the solvent. The resulting material was then punched to form disks of ~15 mm with an electrode thickness of 50 µm. The specific capacity and current density were obtained based on the mass of the electrodes which is approximately 1 mg. Polypropylene membrane Celgard 2325 was employed as the separator, 1 M LiPF3O4 nanoparticles. Fig. 3O4 nanoparticles and Co3O4/RGO nanocomposites. The absorption bands at 586.61 cm−1 and 671.05 cm−1 are assigned to Co-O stretching vibrations and O-Co-O bridging vibrations, respectively. For the pure Co3O4 nanoparticles, the weak absorption bands at 1052.41 cm−1 and 1251.76 cm−1, are assigned to C-O stretching vibrations, the band at 1649.67 cm−1 and the C-H bands near 2980.64 cm−1 are due to the presence of cobalt acetate (Co(CH3COO2)) residues. However, the presence of the O-H band at 3526.79 cm−1 suggests the possibility of adsorbed water. For the RGO-based nanocomposites, some functional groups were still detected. Although the peaks decreased and almost disappeared after the reduction of GO to RGO due to the deoxygenation process, in this case, many peaks were detected due to the partial reduction of GO. Two peaks at 856.9 cm−1 and 1118.05 cm−1 are attributed to the alkoxy and epoxy (C-O) groups, respectively, of GO. The peaks at 1636.34 cm−1 and approximately 2932.70 cm−1 are assigned to the bending of the C=C aromatic rings of RGO and aliphatic C-H groups, respectively. The existence of the C=C peak in the spectra of all the RGO-based samples suggests that the sp2 structure of the carbon atoms was retained. The strong C=C peak observed for Co3O4/RGO indicates a stable graphene structure. Furthermore, the peak centered at approximately 3533.27 cm−1 is attributed to the hydroxyl (OH) groups of GO, as GO is considered to be hydrophilic25.FTIR was used to demonstrate the effect of RGO on the chemical structure of the Co3O4/RGO nanocomposites and the thermal properties were investigated using TGA. The TGA curves of the Co3O4 nanoparticles and their RGO nanocomposites from ambient to 550 °C are shown in Fig. 3O4 nanoparticles shows a weight loss of only 0.6% in a single step. This loss might be due to dehydroxylation of the β-Co(OH)2 species generated during the synthetic process. This result indicates that the Co3O4 nanoparticles are thermally stable with no dramatic mass loss. Based on the weight losses, the TGA curve of the RGO based nanocomposites can be divided into three. In the region from ambient to 100 °C, a clear minor loss of 0.3% is observed for Co3O4/RGO, which is caused by the desorption of physisorbed water. In the second region from 100 to 300 °C, an additional weight loss of 0.7% is observed. The loss in this region results from the decomposition of labile oxygen groups, which includes carboxylate, anhydride, lactone, and epoxy or hydroxyl groups, present in RGO. In the region beyond 300 °C, a weight loss of 0.5% is observed, which results from the decomposition of more stable groups, including carbonyl, phenol, and quinine groups. The total loss of 1.5% shows that all the oxygen-containing groups of GO were converted to RGO during the reduction process. According to the mass remaining after 500 °C, the weight percentage of Co3O4 in the Co3O4/RGO nanocomposites was estimated to be 99%26.The weight percentage of RGO in the Co3O4 nanoparticles and Co3O4/RGO nanocomposites using TEM, as shown in Fig. 3O4 nanoparticles exhibited nanoporous structures27. Using TEM, detailed structures of the Co3O4 nanoparticles and Co3O4/RGO nanocomposites were observed; although pores were not clear, the presence of Co3O4 incorporated on the RGO sheets was observed. In addition to the morphology, the d-spacing of the nanostructures could also be obtained using TEM. The TEM image of a single pure Co3O4 nanoparticle reveals that it has a spherical shape, as shown in Fig. 3O4/RGO nanocomposites clearly shows the Co3O4 nanoparticles and RGO sheets, as shown in Fig. 3O4 crystals. Also, the interlayer spacing of 0.35 nm, indexed to the (002) plane of RGO, is observed in the TEM image of Co3O4/RGO, which matches the results obtained from X-ray diffraction (XRD)28.Morphological studies were performed on both the Co3O4 nanoparticles and Co3O4/RGO nanocomposites exhibited adsorption–desorption isotherms with typical type IV hysteresis loops, a characteristic of mesoporous materials that have different pore sizes as shown in Fig. 3O4/RGO nanocomposites displayed a high BET specific surface area of 57 m2/g, which is four times higher than Co3O4 nanoparticles with a BET specific surface area of only 14 m2/g; this increase in the specific surface area is attributed to the addition of RGO to the Co3O4 nanoparticles. Furthermore, BJH calculations showed that the pore size distributions of the Co3O4 nanoparticles and Co3O4/RGO nanocomposites were found to be in in the range of 80–90 nm.The specific surface area was obtained from the BET isotherms that is a plot of the amount of gas adsorbed as a function of the relative pressure. On the other hand, a plot of pore volume versus pore size gives the pore size distribution and can be calculated using the BJH method. Both the Co3O4 nanoparticles and Co3O4/RGO nanocomposites, CV was first performed in a range of 0 and 3.0 V at a scan rate of 50 mV/s for 3 cycles, as shown in Fig. 3O4 nanoparticles and at 0.67 V for the Co3O4/RGO nanocomposites in the first scan. These peaks resulted from the reduction of Co3O4 to Co metal, the formation of clusters between Co and Li2O, the insertion of lithium into RGO in the case of the Co3O4/RGO nanocomposites and the formation of a solid electrolyte interphase (SEI) layer on the active material9. In the anodic or oxidation scan, two peaks at 1.26 V and 2.28 V for the Co3O4/RGO nanocomposites were observed after the first cycle; these peaks are due to the de-insertion of lithium ions from RGO and the reversible oxidation of Co metal to Co3O430, respectively. However, a weak or almost nonexistent oxidation peak was observed for Co3O4, which could be due to the high scan rate. No significant drop in the peak intensity in subsequent cycles was observed for either the Co3O4 nanoparticles or Co3O4/RGO nanocomposites, suggesting the good reversibility of lithium storage and a high stability11. The electrochemical conversion reaction of Co3O4-based anodes can be described as10:3O4/RGO nanocomposite displayed a higher current than the Co3O4 nanoparticles, which was due to the incorporation of conductive RGO sheets.To study the electrochemical behavior of the Co3O4 nanoparticles and Co3O4/RGO nanocomposites was performed at a current density of 500 mA/g for five cycles, as shown in Fig. 3O4 nanoparticles and Co3O4/RGO nanocomposites, respectively, at the same current density. The Co3O4/RGO nanocomposites exhibited stable cycling performance with 85% capacity retention after the 5th cycle and charge/discharge capacities of 39/36.5 mAh/g, while the Co3O4 nanoparticles showed a dramatic capacity loss with only 48% capacity retention after 5 cycles, evidencing the positive effect of the RGO sheets that led to an enhanced electrochemical response.Typical charge/discharge cycling of the prepared Co3O4 nanoparticles and Co3O4/RGO nanocomposites, the cyclic performance and rate capability were evaluated, as shown in Figs 3O4/RGO nanocomposites showed a more stable cyclic perfomance than Co3O4 with a reversible charge/discharge capacity of 26 mAh/g after the 50th cycle, while the discharge capacity of Co3O4 dropped continuously with each cycle, giving a reversible capacity of only 1.6/1.2 mAh/g after the 50th cycle. Fig. 3O4/RGO nanocomposites. During the first cycle, the Co3O4/RGO nanocomposites exhibited a coulombic efficiency above 100% due to the occurrence of a reverse reaction that involved the embedding of Li2O in the metal particles, which enhanced the electrochemical activity as a result of Li2O decomposition and metal–oxygen bond formation32. Thus, this metal could be oxidized to higher valence states, causing the delithiation capacity to be higher than the lithiation capacity, which resulted in a coulombic efficiency above 100%. The coulombic efficiency of the Co3O4/RGO nanocomposites was 100% after 50 cycles , the charge/discharge capacities were 82.5/77.7 mAh/g.The rate capability of the Co3O4 nanoparticles and Co3O4/RGO nanocomposites, as shown in the Nyquist plots in Fig. 3O4/RGO is smaller than that for Co3O4, which indicates that Co3O4/RGO is capable of faster charge transfer and that it exhibits less internal electrochemical resistance than Co3O4. The sloped lines in the low-frequency region can be attributed to the mass transfer process or the Warburg resistance. The steeper tail for the Co3O4/RGO nanocomposites indicates a lower ion diffusion resistance and enhanced mass transport compared to Co3O4. Thus, the Co3O4/RGO nanocomposites showed high electrical conductivity and rapid charge and mass transfer, which play critical roles in the overall battery performance34.EIS studies were performed for both the Co3O4-graphene37, CuO-graphene38, FexOy-graphene41, Mn3O4-graphene43, SnO2-graphene48 and ZnO-graphene49 nanocomposites. As compared with the results in literature49 shown in Table 3O4/RGO nanocomposites displayed a good reversible capacity of 96.36 mAh/g at 100 mA/g after 100 cycles with the addition of only 1% graphene content as shown in Fig. 3O4/RGO nanocomposites as electrodes. Also, CV at low current and EIS after 100 cycles were also performed as shown in Figs Microwave-assisted techniques has been widely used for the synthesis of graphene based metal oxides as electrodes in lithium-ion batteries which includes Co3O4/RGO nanocomposites at a higher operating temperature of 100 °C. Figure 3O4/RGO nanocomposites performed at 100 °C in the range between 0 and 3.0 V at a scan rate of 50 mV/s for 3 cycles. The Co3O4/RGO nanocomposites exhibited an ideal CV curve of a Co3O4-based anode at 100 °C, with two reduction peaks at 0.86 V and 1.45 V in the first scan. These peaks resulted from the reduction of Co3O4 to Co metal, the formation of clusters between Co and Li2O, the insertion of lithium into RGO and the formation of an SEI layer on the active material9. Two peaks were observed at 1.45 V and 1.96 V in the anodic scan after the first scan, and these peaks are due to the de-insertion of lithium ions from RGO and the reversible oxidation of Co metal to Co3O430, respectively. The overlap between the second and the third cycles indicates the enhanced cycling stability of the Co3O4/RGO nanocomposites50. Furthermore, the current response of Co3O4/RGO increased with stronger and sharper peaks when the operating temperature was 100 °C, which indicates the role of the high temperature in enhancing the CV performance of the Co3O4/RGO nanocomposites.Further electrochemical investigations were performed to test the electrochemical performance of the Co3O4/RGO nanocomposites measured at an operating temperature of 100 °C with a current density of 500 mA/g for 5 and 50 cycles are shown in Fig. 2O into the metal particles.The galvanostatic charge/discharge capacities of the Co3O4/RGO nanocomposites at high operating temperature, EIS tests were conducted, as shown in Fig. 3O4/RGO (Fig. 3O4/RGO in the low frequency region of the spectrum measured at 100 °C (Fig. 51.To further investigate the electrochemical behavior of the CoRGO Fig.  at room RGO Fig. , the sem °C Fig.  relative °C Fig.  is an in3O4 nanoparticles and Co3O4/RGO nanocomposites via a microwave-assisted route. FTIR spectroscopy confirmed the formation of graphene-based Co3O4 nanoparticles. Co3O4/RGO nanocomposites’ thermal stability was determined using TGA. Morphological studies using TEM further confirmed the formation of Co3O4 nanoparticles in addition to Co3O4 nanoparticles supported on RGO. The prepared Co3O4/RGO nanocomposites showed excellent electrochemical behavior as anodes in li-ion batteries. A superior electrochemical response which includes enhanced charge/discharge capacity and cycling stability was observed. The enhanced electrochemical performance relative to that of the pure Co3O4 nanoparticles, even when high current densities are applied, is attributed to the incorporation of 2D graphene, which resulted in a surface area almost four times larger than that of pure Co3O4, and to the exfoliation and good integrity of the RGO sheets in the Co3O4/RGO nanocomposites, as determined from chemical and thermal studies. Furthermore, increasing the operating temperature from ambient to 100 °C further enhanced the electrochemical performance, making the prepared nanocomposites potential for high temperature li-ion batteries.We successfully prepared CoEnhanced Electrochemical performance at high temperature of Cobalt Oxide/Reduced Graphene Oxide Nanocomposites and its application in lithium-ion batteries


Redox active cysteine residues including βCys93 are part of hemoglobin's “oxidation hotspot”. Irreversible oxidation of βCys93 ultimately leads to the collapse of the hemoglobin structure and release of heme. Human fetal hemoglobin (HbF), similarly to the adult hemoglobin (HbA), carries redox active γCys93 in the vicinity of the heme pocket. Site-directed mutagenesis has been used in this study to examine the impact of removal and/or addition of cysteine residues in HbF. The redox activities of the recombinant mutants were examined by determining the spontaneous autoxidation rate, the hydrogen peroxide induced ferric to ferryl oxidation rate, and irreversible oxidation of cysteine by quantitative mass spectrometry. We found that substitution of γCys93Ala resulted in oxidative instability characterized by increased oxidation rates. Moreover, the addition of a cysteine residue at α19 on the exposed surface of the α-chain altered the regular electron transfer pathway within the protein by forming an alternative oxidative site. This may also create an accessible site for di-sulfide bonding between Hb subunits. Engineering of cysteine residues at suitable locations may be useful as a tool for managing oxidation in a protein, and for Hb, a way to stave off oxidation reactions resulting in a protein structural collapse.  Thus, protein engineering strategies such as site-directed mutagenesis can be utilized to develop a better understanding and control oxidative reactions within the protein. The most significant oxidation-prone sites in HbA when reacting with HIn HbF there is one cysteine residue per subunit, at positions αCys104 and γCys93. Three mutants of HbF were created in this study to explore the oxidative influence of cysteine residues in HbF. α19 Ala→Cys (αA19C), γ93 Cys→Ala (γC93A) and double mutant αA19C/γC93A. None of these mutations have been found as natural mutations according to the database of Hb variants 22.1Escherichia coli BL21 (DE3) for expression.The gene expressing wildtype recombinant HbF (rHbF) was previously inserted into the pETDuet-1 plasmid from Novagen 2.2E. coli containing rHbF, αA19C, γC93A or αA19C/γC93A were all cultivated in the same manner and the expression and purification procedures were based on previous protocols D-1-thiogalactopyranoside  and supplemented with 0.24 mM δ-aminolevulinic acid (Sigma-Aldrich). The cultures were briefly bubbled with carbon monoxide gas (CO) and then cultivated overnight in 30 °C at 150 rpm. CO gas was bubbled into the cultures directly after terminating the cultivation to stabilize the Hb in CO-liganded form. The cells were processed according to aforementioned protocols up until removal of host contaminating proteins, which was performed by liquid chromatography on an ÄKTA Avant 25 system  involving two ion exchange purification steps. All buffers were prepared with ultrapure water , filtered and degassed before use. The first step involved a cation exchange column, packed with 65 ml Capto S media  in a HiScale 26/20 column . The flow velocity was 153 cm/h. The Hb bound to the column pre-equilibrated with 10 mM sodium phosphate (NaP) buffer pH 6.0 and was released by isocratic elution with 70 mM NaP buffer pH 7.2. After exchanging the sample buffer to 20 mM Tris-HCl pH 8.3 using a Sephadex G-25 desalting column , the second chromatography step was anion exchange with a HiTrap Q HP 5 ml column . A linear gradient elution to 50 mM sodium phosphate buffer pH 7.2 supplemented with 100 mM NaCl resulted in pure fractions of Hb. Additionally, the αA19C and αA19C/γC93A samples were supplemented with 10 mM DTT  and incubated 20 min on ice before being applied onto the Q HP column in order to reduce possible disulfide bond formation between the polypeptide chains. The Hb solutions were finally concentrated by centrifugation with Vivaspin columns  and snap-frozen in liquid nitrogen in the CO-liganded state and stored at − 80 °C. The purity was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and the gel was analyzed densitometrically using a Molecular Imager Gel Doc XR System, with Quantity One software (Bio-Rad Laboratories). The amino-terminal Met residues were removed (> 95%) as determined by mass spectroscopic measurements.The 2.3L-cysteine (Sigma-Aldrich). The purified proteins were also analyzed by dynamic light scattering (DLS) in a Zetasizer Nano S instrument . The Hb samples were diluted to 0.5, 1.5 and 5.0 mg/ml in 50 mM NaP buffer pH 7.2, and measured at 20 °C. First without DTT, and then incubated with addition of 10 mM DTT for 10 min and measured again. Oxygen equilibrium curves of all recombinant proteins were recorded on a Hemox Analyzer  in 10 mM potassium phosphate buffer pH 7.4 supplemented with 100 mM NaCl at 37 °C, as described previously Ellman's reagent , Thermo Scientific) was used to quantify the cysteine content in the Hb samples. The reaction buffer (100 mM NaP buffer pH 8.0 + 1 mM EDTA), Ellman's reagent (71.4 µg/ml) and Hb samples were mixed and incubated at room temperature for 15 min before measurement of absorbance at 412 nm, according the manufacturer's protocol. The sample absorbance was compared to a standard curve prepared with 2.42-liganded form by exposure to a continuous stream of oxygen gas under bright light. The conversion from CO-liganded state to the oxy-form was confirmed by spectral shift resulting in peak maxima at 415, 540 and 576 nm, followed by buffer exchange to 100 mM NaP buffer pH 7.4 using a Sephadex G-25 desalting column. The concentration of Hb was confirmed by addition of sodium dithionite (Sigma-Aldrich) to a small portion of the sample, converting it to the deoxy-form, and using the millimolar extinction coefficient 133 mM−1 cm−1 at absorbance peak 430 nm. The autoxidation of 20 μM Hb was monitored with Cary60 UV–vis spectrophotometer (Agilent Technologies) at 25 °C during 24 h, with or without addition of superoxide dismutase (SOD) and catalase at concentrations of 4.6 U/ml and 414 U/ml, respectively. The rate of autoxidation was determined by following the decrease in absorbance at 576 nm over time. The data were fitted to a single exponential equation.Hb samples were thawed, kept on ice, and fully converted into the ferrous O2.53[Fe(CN)6] (Sigma-Aldrich), incubated on ice, and exposed to visible light for complete conversion to the ferric form (Fe3+). The samples were then loaded on Sephadex G-25 desalting columns equilibrated with 40 mM NaP buffer pH 7.2 to remove the surplus of potassium ferricyanide. The concentration of Hb was determined as described before and sample solutions of 20 μM Hb were prepared. H2O2 solutions at concentrations of 200, 400, 400, 600, 800 and 1000 µM were prepared freshly the same day with ultrapure water, kept on ice and away from light until the start of the experiment. The oxidation reaction of ferric Hb and H2O2 were performed in a stopped-flow experimental setup, previously described by Ratanasopa et al. 2O2 were mixed rapidly with the RX-2000 Rapid Mixing Stopped-Flow Accessory  and the reaction was followed at 405 nm in a Cary 60 UV–vis spectrophotometer (Agilent Technologies). The data were fitted to a double exponential equation. The obtained rate constants were plotted against H2O2 concentration and fitted to a linear equation.The Hb samples were thawed, mixed with 1:1.5 excess of potassium ferricyanide (K2.62O2 and then incubated overnight in 20 mM NaP pH 7.4 at 25 °C to replicate oxidative conditions. All samples were then processed and treated with trypsin as previously described 2O2). The precursor ion mass tolerance was ± 10 ppm and the fragment ion mass tolerance was ± 0.025 Da. Extracted ion chromatograms of modified (and unmodified) tryptic peptides were used to quantify oxidative differences. For relative quantification, the ratio of each oxidized hotspot peptide was calculated based on the sum of the extracted ion chromatogram (XIC) peak area of all forms (oxidized and unmodified) to be 100%.178 µM of each recombinant protein recombinant proteins  was converted to the oxy-form treated with incremental doses  of H2.7Heme loss from the different recombinant Hbs was examined by utilizing heme scavenger apomyoglobin H64Y/V67F (apoMb) according to the method developed by Hargrove et al. 2.8t-tests.All experimental reactions were replicated a minimum of three times (n = 3), and mean values and standard deviations were calculated. The Microsoft Excel Solver program was used to fit the time courses obtained to exponential functions. Statistical significance (P < 0.05) was determined by unpaired 3E. coli and purified successfully. The obtained yields 0.7–1.1 mg Hb/g cells and 6.0–9.3 mg Hb/l culture were well within previously reported range of wildtype rHbF production The correctness of the DNA sequences of the wildtype and the three mutants were confirmed by Sanger sequencing. All recombinant proteins were subsequently expressed in It was observed that αA19C and αA19C/γC93A, both containing additional cysteine located on the surface exposed part of the α-chain, behaved slightly differently compared to wildtype rHbF during purification. The cell lysate filtration of these two mutants was more laborious. Also, the elution profile of the second chromatography step for these mutants showed some differences. In order to verify the composition of the altered elution profile fractions, dithiothreitol (DTT) was added. When analyzed by Q HP chromatography, an elution profile similar to the one obtained with rHbF was generated . The addOxygen binding equilibriums were examined by generation of oxygen binding curves (OBC) in a Hemox Analyzer. All recombinant proteins successfully bound and released oxygen, and the cysteine mutations had no particular influence on the oxygen binding property of HbF . These dAutoxidation experiments were performed to examine the properties of the mutants compared to rHbF. The study was performed both with and without the presence of SOD and catalase. As seen in the 2O2 concentrations in a stopped-flow spectrophotometer. The linear slope attained by plotting the rate constants found for rHbF and the three mutants against the H2O2 concentration gives the second order rate constant of the reaction and the results are presented in γ represents the oxidation of the γ-chain and the kα the oxidation of the α-chain To further study the oxidative behavior of the HbF mutants, the ferric form of the recombinant Hbs was exposed to increasing H2O2 on post-translational oxidation of oxidative hotspots in Hb, quantitative mass spectrometry was utilized to target all peptide charge states. Extracted ion chromatograms (XICs) were generated from the most abundant monoisotopic peak of each peptide isotopic profile and the resulting ratio differences were compared for oxidized and non-oxidized hotspot peptides. All amino acid oxidations identified by LC-MS/MS analysis  in this study correlated with previously published data 2O2 increases in a manner consistent with previously published data 2O2 doses. αA19C resulted in lower levels of C93 oxidation compared to rHbF; for example 10X H2O2 resulted in nearly a 2-fold lower ratio for αA19C  have been reported 2+-O2 autoxidizing to ferric HbFe3+ in HbA et al., autoxidation rate of mouse Hb when exposed to H2O2 was decreased when the Hb carried two cysteines in the β-chain, compared to the variant with just a single cysteine. Rerouting of oxidation patterns within a subunit may thus provide protection against an oxidizing environment. The results from the autoxidation in this study provide supplementary evidence of reorganization of electron pathways through addition of cysteine residues, not just within a single subunit, but between different subunits. This electron transfer reaction may prove particularly beneficial in an oxidizing environment.The autoxidation studies showed that cysteine removal from γ93 resulted in higher autoxidation rate for both mutants harboring this mutation. This could be explained by the conserved cysteine residue acting as a superoxide scavenger and forming a thiyl radical upon HbFe2O2 in the stopped-flow experiments showed that the γ-chain was compromised by the γC93A mutation, resulting in a higher oxidation rate in the γ-chain for those two mutants. On the other hand, the αA19C mutant again produced results indicating that oxidation rate is slightly lower, both in the γ-chain and the α-chain, compared to rHbF. Furthermore, in the double mutant αA19C/γC93A, a lower oxidation rate in the γ-chain was found. These findings additionally indicate that the cysteine on the surface of the α-chain protein provides protection from oxidative reactions in the γ-chain. Analysis of the oxidation states of different cysteine residues after exposure to oxidizing conditions with H2O2 using quantitative mass spectrometry, confirmed electron transfer from the heme vicinity of the γ-chain to the surface exposed residue α19 of the α-chain. The data obtained in this study suggest that wildtype rHbF is less oxidatively stable and resistant to autoxidation than the αA19C mutant. In previous work, it was shown that conserved Cys93 is the prominent endpoint for free-radical induced Hb oxidation, while oxidation at other residues (in β or α) is usually negligible Oxidation of the ferric form to ferryl form by HHeme loss studies were conducted to elucidate if the mutations produced any changes regarding possible release of heme. As free heme has been shown to be a damage-associated pattern molecule The findings from this study can also be of interest to a more applied Hb research in the field of oxygen therapeutics. Cell-free Hb is used as the principal component but the oxidative reactions of the protein present problems that must be resolved. In this study, the focus has been on protein engineering of HbF as a substitute for HbA due to its reported potential advantages as a starting material for oxygen therapeutic development 52O2 oxidation of ferric Hb in a stopped-flow setup, as well as analyzing quantitative mass spectrometry data after H2O2 exposure. It was especially evident that the cysteine at α19 in the double mutant αA19C/γC93A showed significantly increased oxidation, acting as a compensatory hotspot when cysteine in the γ-chain was removed. αA19C mutation also contributed to a slower heme loss in the γ-chain.As previously confirmed by studies of native HbA and recombinant mutants of βCys93, this conserved residue plays a central role in the redox reactions of Hb. From the findings presented here, there are indications that γCys93 has a role as a possible superoxide scavenger during spontaneous autoxidation. In this study, it was also established that addition of a cysteine residue in the α-chain at position α19 can influence electron transfer within the HbF molecule. This was confirmed by analyzing oxidative reactions such as rates of autoxidation and H2O2. Amino acid substitutions through protein engineering of the Hb molecule result in properties that may prove beneficial for an oxygen therapeutic starting material. However, the lessons learned from previous attempts need to be considered and the understanding of the multifaceted biochemistry of the Hb molecule should be extended in the strive to achieve a viable protein for oxygen delivery in clinical settings.The overall findings of this study are that the mutations of HbF studied produced functional proteins that exhibited normal Hb functions. The addition of cysteine at α19 produces a readily accessible site on the protein surface that is able to form di-sulfide bonds. The removal of cysteine from the γ-chain at position 93 in HbF resulted in a more oxidatively unstable protein, while addition of cysteine on the surface of the α-chain appears to provide protection from adverse oxidative reactions resulting from exposure to H


A set of new diabatic potential energy surfaces (PESs) of the NaH2 system are structured, which include the diabatic coupling between the lowest two adiabatic states. The electronic structure calculations are performed on the multi-reference configuration interaction level with the cc-pwCVQZ and aug-cc-PVQZ basis sets for Na and H atoms. 32402 geometries are chosen to construct the diabatic data by a unitary transformation based on the molecular property method. The diabatic matrix elements of The Na(3p) + H Among the issues of reactive collision for these alkali elements, the reactions of K4, Rb6, and Cs9 with H2 proceed by a harpoon model, whereas the reactions of Li13 and Na16 with H2 follow an insertion mechanism.The interactions between electronically excited alkali atoms and hydrogen molecule, including both no-reactive quenching and chemical reactions, have become an interesting topic due to the special advantage for understanding diabatic processes. For the collisions of excited alkali atoms with H2 presents a simple prototype of such collision systems, and numerous experimental results22 about the collisions between excited sodium atom and hydrogen molecule are available. Botschwina et al.17 performed crossed molecular beam experiments on the Na(3p) + H2 → Na(3 s) + H2 process. The results of quenching cross section and vibrational energy distribution were presented in their work. Bilililign et al.15 studied the Na(4p) + H2 → NaH + H photochemistry reaction by using the “half-collision” pump-probe technique. They observed a bimodal rotational distribution of the NaH product: the minor peak at lower rotational states is due to the repulsive interaction, while the major peak at higher rotational states is attributed to the attractive interaction. Motzkus et al.20 applied three different nonlinear optical techniques, including coherent anti-Stokes Raman scattering (CARS), resonance-enhanced CARS, and degenerate four-wave mixing, to compare the Na(4p) + H2 and Na(3p) + H2 reaction processes. This experiment showed the formation of NaH via the Na(3p) + H2 reaction follows a two-step mechanism, which is opposite to the direct reaction of Na(4p) + H2. In 2008, Chang and co-workers22 studied the rotational and vibrational state distributions of NaH in the reactions of high exited states Na with H2 by using the pump-probe technique. The authors concluded that the Na(62S) reaction has a dramatically reduced ionization energy, and the corresponding reaction pathway maybe prefer a harpoon model via a near collinear configuration. For the Na(62S) + H2 reaction, the valence electron of Na hopping mechanism is involved to form an ion-pair Na+H2− intermediate.The NaH27 have also been performed on the NaH2 system based on several potential energy surfaces (PESs)33, which were concentrated on studying the effect of conical intersection and the processes of electronic-to-rovibrational energy transfer. In 1982, Donald et al.28 calculated the lowest three PESs and diabatic coupling for the Na(3p) + H2 quenching process by using the diatomics-in-molecules (DIM) method. Then they used a new parametrization for the diabatic potential energy curves of NaH29 to optimize the preceding PESs, which are only suitable for studying the non-reactive quenching of the Na(3p) + H2. In 1999, Michael et al.30 structured an analytical potential energy matrix of the NaH2 system for the lowest two states based on MP2 calculations, which only include a small number of ab initio energy points near the region of conical intersection. The potential energy matrix can be applied in reaction dynamics calculations of the diabatic processes.Extensive theoretical studies2 plays an important role for studying diabatic reaction dynamics correlated with two adiabatic states. The reaction starts at the adiabatic 22A′ surface and then intersects the adiabatic 12A′ surface to enter into the product channel. The formation of NaH molecule by this reaction follows a two-steps process. The first step is the quenching between Na(3p) and H2,2,The reaction of lowest electronically excited state Na(3p) with H21. However, the quantum dynamics study of the Na(3p) + H2(X1Σg+) → NaH(X1Σ+) + H(2S) reaction has not been reported. For the title reaction, the early diabatic PESs may be not accurate enough to investigate the state-to-state reaction dynamics due to the limit of computational conditions. Fortunately, the recent advances in ab initio theory and the neural network (NN) model make it possible to obtain accurate global PESs. In this work, a set of new diabatic PESs involved two lowest adiabatic states (12A′ and 22A′) and the coupling between them are structured with the NN method. To guarantee the accuracy of the new diabatic PESs, numerous high precision single point energies in a wide coordinate range are calculated, which are used to construct the energy matrix in the diabatic representation by the molecular property method. Then the time-dependent wave packet (TDWP) calculations are carried out on the new diabatic PESs to obtain the quantum dynamics information of the title reaction.The correctness of this process has been proved by rate equation modelRNa-HH at four fixed internuclear distances of HH  in C2v geometry. The electronic symmetry of the ground and first excited states turn into 12A1 and 12B2 in C2v geometry, respectively. It can be seen that the adiabatic potentials strongly avoid, while the curves in the diabatic representation cross over each other smoothly near the crossing point. The crossing point located at larger RNa-HH with the rHH increasing. Moreover, the adiabatic and daibatic potential energy curves are overlapping when RNa-HH is far away from the crossing point, implying the electronic coupling is zero in the asymptotic region.Figure 2 molecule, respectively. The HH bond length is set to the equilibrium distance (1.401 bohr) corresponded the ground electronic state. No obvious well or barrier can be found on the 2 molecule. There exists a wide well around the H2 molecule on the a0, y = 4.1 a0. The Na atom can be attracted by the well to form the metastable intermediate when it moves to the H2 molecule, and the intermediate enters product channel to dissociate to the NaH + H on the Figure entclass1pt{minima2 channel on the . For the 2 and NaH + H channels, respectively. Thus in the diabatic representation, the 2 to NaH + H. For the lower panel of Fig. 2 is dominated by an insertion approach. Combined with previous studies, it could conclude that the reactions of low-lying electronic states Na with H2 follow an insertion model, whereas the reactions of highly-excited states Na with H2 could favor the harpoon-type mechanism. Moreover, taking into account the zero point energies of H2 (0.271 eV) and NaH (0.072 eV) molecules, the endothermicity for forming the NaH molecule is about 0.63 eV.The diabatic mentclass2pt{minimJ values. The curve of J = 0 shows the reaction threshold is about 0.63 eV, corresponded with the endothermicity calculated on the PESs, implying the title reaction occurs by a barrierless path in the product channel. The threshold increases at large J value due to the increasing centrifugal barrier. Some sharp resonance peaks can be found due to the potential well on J value increasing, which is attributed to the large centrifugation potential leads to more Na atoms entrance the product channel without the well, thus the lifetime of complex becomes shorter.Figure J value is calculated up to 70, which can ensure the convergence of integral cross sections (ICSs) and differential cross sections (DCSs) when the collision energy is below 1.5 eV. The ICS results of the Na(3p) + H2 reaction are similar to the Li + H2 reaction34. The ICSs curves are relatively smooth, compared with the oscillating reaction probability curves. The total ICS and several vibrational states (v′ = 0 − 6) ICSs of the title reaction are displayed in Fig. In the TDWP calculations, the maximum Furthermore, the product rotational distribution for three selected collision energies  are calculated, which are shown in Fig. The DCS gives the product angular distribution of a reaction. Figure 2 system are constructed in the diabatic representation, which are correlated with the adiabatic 1 A′state and 2 A′state. The ab initio calculations are performed at the internally contracted multi-reference configuration interaction level with the Davidson correction (icMRCI + Q). The aug-cc-PVQZ and cc-pWCVQZ and basis sets are adopted for H atom and Na atom, respectively. The diabatic matrix elements are generated by the transformation of ab initio data based on the molecular property method. A mass of geometries (32402) in a large coordinate space are selected to fit the diabatic PESs using the NN model, and the root mean squared errors (RMSEs) for the diabatic terms 2(X1Σg+) → NaH(X1Σ+) + H(2S) reaction are carried out to obtain the rigorous quantum dynamics information. The dynamics results show the reaction threshold is consistent with the endothermicity obtained from the diabatic PESs. There exist some oscillation structures on the reaction probability curves due to the complex forming in the potential well. The total ICS steeply rises when the collision energy below 1.5 eV, and the rovibrational states ICSs of the product NaH molecule are presened. In addition, the product NaH molecule tends to be forward scattered, and the forward bias becomes more obvious with increase of the collision energy. As we know, there is no available experimental study which can directly examine the present results. We anticipate our studies could serve as a reference of future experiments for the title reaction.In the present work, a set of new global PESs for the NaH42 have been developed, and the most important step is to obtain the transformation matrix between the diabatic and adiabatic representations. An effective transformation approach with less calculation burden is to use appropriate molecular properties associated with the transition of electronic states to construct the matrix, and the dipole moment is selected for the NaH2 system. A brief description about the diabatization scheme is presented below. In this work, the diabatic coupling includes two electronic states, thus the unitary transformation from the adiabatic basis α is called the mixing angle. The energy matrix elements at the diabatic representation is calculated as follows2A″ which is not involved in the electronic coupling, and α is calculated bySeveral diabatization methodsmentclass2pt{minim2A′ and 22A′ adiabatic states for the NaH2 system are calculated in Cs symmetry using the icMRCI + Q method with a complete active space self-consistent field (CASSCF) reference wave function. In the state-averaged CASSCF calculations, three electronic states  of NaH2 are assigned to equal weight. Three valence electrons are in fifteen active orbitals (11a′ + 4a′′), consisting of two 1 s orbitals on H, and 3 s, 3p, 3d, 4 s and 4p orbitals on Na. The frozen-core approach is used in the MRCI calculations, and the orbitals (4a′ + 1a′′) are set to close, thus three electrons are included in the calculations of correlation energy. The aug-cc-PVQZ and cc-pWCVQZ basis sets are used for H atom and Na atom, respectively. A total of 32402 geometries are selected to structure the diabatic energy matrix in the Jacobi coordinates. The energy points are defined by 0.6 ≤ rHH/a0 ≤ 28, 0 ≤ RNa–HH/a0 ≤ 35, 0 ≤ θ/degree ≤ 90 for the Na−HH region, and 0.8 ≤ rNaH/a0 ≤ 28, 0 ≤ RH–NaH/a0 ≤ 35, 0 ≤ θ/degree ≤ 180 for the H−NaH region. All of the ab initio calculations are implemented by MOLPRO package43.The electronic structures of the 150. The feed-forward NN is employed in this work. The NN consists of a set of input signal {xi}, one output signal corresponded to energy and two hidden layers. The output signal of a neuron can be presented aswi and bj are the weights and bias of interconnecting neurons, respectively. The linear function as the transfer function f(x) in the output layer, and the hyperbolic tangent function is chosen in the two hidden layers, which is written asThe energies in the diabatic representation are constructed by combining the adiabatic data with the diabatic transformation based on molecular property method. All of the diabatic energies are used to fit the diabatic terms of 52 are used in the fitting of each diabatic term. To prevent overfitting, all of the diabatic energies are randomly divided into the training (90%), validation (5%) and testing (5%) sets. The final fitting energy can be expressed asIk are input data after corresponding geometries preprocessing. For the fitting of The permutation invariant polynomials255 are shown in Table To examine the accuracy of fitted diabatic PESs, the comparison between spectroscopic constants of Hmentclass2pt{minim2(X1Σg+) → NaH(X1Σ+) + H(2S) reaction is carried out by the TDWP method on the new NN diabatic PESs, which has been described in detail previously57. This method is effective to treat the diabatic transition between two electronic states, and only an online involved the main equations is presented below. In the body fixed representation, the Hamiltonian of the Na + H2 reaction is written as followsR is the distance between Na and HH center of mass, and r represents HH bond length. µR and µr denote the reduced masses relevant to R and r. J and j are the total and H2 molecular angular momentums. 2 system. The reactant coordinate based method is used to obtain the S-matrix at the product channel, which is developed by Sun et al.58. The states resolved reaction probability can be calculated byThe quantum dynamics simulation for the Na(3p) + Hθ denotes the scattering angle between the incoming Na (3p) + H2 and the scattered NaH + H, and The states selected ICSs and DCSs are calculated by the following equations2  → NaH + H are performed the TDWP calculations, and the main dynamics parameters are given in Table In this work, only the ground rovibrational state reaction of Na(3p) + H


Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (Dh4) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (hO) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8]  and [U(CO)8]  have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium.The octacarbonyl cation and anion complexes of actinide metals [An(CO) The associated electron‐counting rules, specifically, octet rule for main‐group atoms, 18‐electron rule for transition metals, and 32‐electron rule for lanthanides and actinides, had already been suggested by Langmuir in 1921 prior to the advent of modern quantum chemistry.The classification of chemical elements in the periodic table, introduced 150 years ago by Mendeleyev,p(n−1)dn−f valencen)s and (n)p atomic orbitals (AOs) of the main‐group atoms are both very important for the chemical bonds, with the first octal‐row elements exhibiting a special role owing to the similar radii of the s and p functions.n)p AOs of the heavier main‐group atoms with n>2 are significantly larger than the respective (n)s AOs, which leads to significantly different bonds and increasing stability of the lower oxidation states of the heavier atoms; this is further enhanced by the filling of the d shells and relativistic effects for the very heavy atoms.n−1)d valence orbitals are usually much more important than the (n)s and (n)p AOs.n)p AOs are not genuine valence orbitals for transition metals and that the 18‐electron rule should be replaced by a 12‐electron rule based on a (n)s(n−1)d valence shell.n)p AOs of the transition metals has recently been demonstrated.The relative contribution of the different valence orbitals towards bonding interaction is an important factor to determine the chemical behavior of the atoms. The , we found that the 32‐electron rule is valid in the systems that have 32–34 valence electrons when the symmetry of the orbitals is considered.8]− anion complexes are dominated by [Ln(d)]→(CO)8 π backdonation and [Ln(d)]←(CO)8 σ donation. The metal f orbitals play a very minor role in the interatomic interactions, because the 4f orbitals of the lanthanides have a strongly contracted radial distribution.The relevance and the role of the f orbitals for the chemical bonds in lanthanide and actinide compounds is less clear. Pseudopotentials, in which the f electrons are part of the effective nuclear potential, have a similar accuracy as those with explicit consideration of f electrons in the valence shell.5Me5)3U(CO)], [(C5H4SiMe3)3U(CO)], and [(C5Me4H)3U(CO)], have been isolated,n (n=1–6) have been produced in solid noble gas matrices.8]+ cation complex has also been studied in the gas phase by using infrared photodissociation spectroscopy.5Me5)3Th(CO)][BPh4], which is isolable at room temperature, has also been reported and reveals a slightly redshifted carbonyl absorption at 2131 cm−1.5Me5)3‐based orbitals in the thorium carbonyl complex.We extended our work to carbonyl complexes of the early actinide atoms thorium and uranium. Previously, stable heteroleptic uranium carbonyl complexes, such as q, and we analyze the nature of the metal–CO bonds with the f orbital participation in the metal–CO bonds being quantitatively explored. For completion, we also report the computed results of the neutral octacarbonyl complexes [Th(CO)8] and [U(CO)8]. We address the question about the validity of the electron‐counting rules for the actinide octacarbonyl ions. Recent studies by us showed that the 18‐electron rule for transition‐metal complexes is valid for the formal 20‐electron systems [TM(CO)8]−  when the symmetry of the valence orbitals is considered.8] , which have cubic (hO) symmetry and a triplet (X3A1g) electronic ground state.Herein, we report an infrared photodissociation spectroscopic and theoretical study of actinide octacarbonyl ion complexes +/− , including the neutral ones. The optimizations at different spin states were performed at the B3LYP‐D3(BJ)−4 and RMS displacement (ConvX) of 4*ConvF as threshold values. The maximum force and the maximum displacement are scaled as 1.5*ConvF and 1.5*ConvX.Quantum chemical calculations that used density functional theory (DFT) were carried out to obtain the equilibrium geometries and vibrational spectra of the actinide complexes +. This is the only homoleptic thorium carbonyl complex observed in the cation mass spectrum. In addition, the mass spectrum also contains ions of the form [OTh(CO)n]+ with n=4–6. More peaks are observed in the anion spectrum, as shown in Figure m/z=456, which corresponds to the mass of [Th(CO)8]−, and the isotopic shift agrees with the thorium octacarbonyl assignment. Besides [Th(CO)8]−, the mass spectrum also shows a series of peaks that can be assigned to [ThCxOy]− with x>y. The observation of these anions suggests that some carbon monoxide molecules are dissociated during the pulsed laser ablation‐supersonic expansion process in the ion source.The mass spectra of thorium carbonyl ions are shown in Figure + peak, the most abundant species is [OU(CO)7]+ followed by [U(CO)8]+ and [UO2(CO)5]+ (2a). Notably, these uranium carbonyl complexes were also observed to be the most abundant species in a previous report.2− and [UO2(CO)4]−. The [U(CO)8]− is also observed with appreciable intensity 8]− anion gives only one band at 1885 cm−1. These band positions are strongly redshifted with respect to free CO (2143 cm−1), which indicates significant metal→CO π backdonation. The [Th(CO)8]+ and [U(CO)8]+ cations each display a single band at 2074 and 2087 cm−1, respectively. The band positions of the cations are about 200 cm−1 blueshifted from those of the anions, but they are still redshifted with respect to free CO. The band position of [U(CO)8]+ cation is in agreement with the previously reported value of 2080 cm−1.13CO)8]− and [Th(13CO)8]+ are also measured . The band positions are observed at 1827 and 1879 cm−1 for the anion and at 2029 cm−1 for the cation. The isotopic frequency shifts confirm that these bands are due to carbonyl stretching vibrations.The octacarbonyl anions and cations are mass‐selected for infrared photodissociation. The loss of one CO ligand takes place when the species are excited with unfocused infrared light in the carbonyl stretching frequency region. The infrared spectra are shown in Figure 8]q  at the B3LYP‐D3(BJ)/def2‐TZVPPD/ECP level . The thorium octacarbonyl ions possess Dh4 symmetry, with the [Th(CO)8]+ cation having a 2A1g electronic ground state and the [Th(CO)8]− anion possessing a 2B1u ground state. Neutral complex [Th(CO)8] has cubic (hO) symmetry and a singlet (1A1g) electronic ground state. The uranium octacarbonyl ions also exhibit cubic (hO) symmetry, with the [U(CO)8]+ cation having a sextet (6A1g) electronic ground state and the [U(CO)8]− anion possessing a quartet (4A1g) ground state. Neutral [U(CO)8] has Dh4 symmetry and a quintet ( 5B1u) electronic ground state. The calculated C−O distances of all molecules are slightly longer than in free CO (1.125 Å). The different equilibrium geometries of the molecules may be caused by Jahn–Teller distortion. Calculations that used different starting geometries led to the same equilibrium structures.Figure 7]q complexes). The dissociation of one CO ligand from the thorium species [Th(CO)8]q has very similar values between De=20–22 kcal mol−1 for the charged and neutral complexes. Nearly the same values are calculated for CO ligand dissociation from cationic [U(CO)8]+ and neutral [U(CO)8] complexes, whereas the anion [U(CO)8]− has a slightly larger BDE. The BDEs for loss of one CO from the octacarbonyls are much greater than the energy of the infrared photons in the CO stretching region. Therefore, the experimentally observed dissociation is due to a multiphoton absorption process. The total BDEs of all eight CO ligands are rather high: the values are between 203–245 kcal mol−1 for the thorium adducts and 170–249 kcal mol−1 for the uranium complexes.Table 8]q. There is only one experimentally observed IR active mode of the uranium cation and anion [U(CO)8]q  that possesses hO symmetry, which are redshifted by −56 cm−1 for the cation and −258 cm−1 for the anion with respect to free CO. This is in excellent agreement with the theoretical values, which suggest a redshift of −63 and −243 cm−1, respectively. The agreement between the theoretical and experimental wavenumbers for the C−O stretching mode strongly suggests that the observed species are the uranium complexes [U(CO)8]+ in the sextet (6A1g) ground state and the [U(CO)8]− anion in the quartet (4A1g) state. The calculations predict that the uranium octacarbonyl complex [U(CO)8], exhibiting Dh4 symmetry, has two IR‐active CO stretching modes, which are redshifted by −146 and −153 cm−1.Table 8]q  that possess Dh4 symmetry predict that there are two IR‐active C−O stretching modes with high intensities. There are two experimental values in the C−O stretching region of the IR spectrum for the anion, but only one signal is observed for the cation 8]+ cation in the 2A1g electronic ground state and the [Th(CO)8]− anion in the 2B1u state. The calculations predict that the neutral thorium octacarbonyl complex [Th(CO)8], having hO symmetry, exhibits a single IR‐active stretching mode, which is redshifted by −149 cm−1.The calculations of the thorium ions −  showed that the 4f orbitals of the Ln atoms provide <4 % of the total orbital interactions of the Ln−−CO bonds. The dominant covalent bonding comes from Ln(d)−→CO π backdonation and Ln(d)−←CO σ donation, which account for >90 % of the orbital interaction.We theoretically analyzed the metal–CO bonds of the octacarbonyl complexes with the EDA‐NOCV method to gain insights into the nature of the interatomic interactions. A central question of the bonding analysis concerns the contributions of the metal valence orbitals to the bonds. The EDA‐NOCV method is well suited for this, because it uses the electronic structure of the molecules for an unbiased analysis of the pairwise orbital interactions without referring to a reference system. This has been found very useful in our previous studies of metal octacarbonyl complexes of main‐group atoms,8]q complexes is simplified by the high symmetry of the structures, because the metal AOs split according to the irreducible representation of the point group. Figure q with 7s, 7p, 6d, and 5f valence orbitals and eight CO in the cubic (hO) field of [U(CO)8]q. The eg MO is fully occupied in the quartet (4A1g) state of the anion [U(CO)8]−, whereas it is occupied with two unpaired electrons in the sextet (6A1g) state of the cation [U(CO)8]+. It becomes obvious that the electronic reference configuration of U+ in the sextet state is 7s0 7p0 6d2 5f3, whereas the quartet state of U− has the electron configuration 7s0 7p0 6d4 5f3. The AOs of the uranium atom uniquely correlate with the MOs of the complexes [U(CO)8]q, except for the t1u component of the 5f AOs, which can mix with the t1u set of the 7p AOs. However, inspection of the deformation densities, which are provided by the EDA‐NOCV calculations, makes it possible to estimate the relative contributions of the metal 5f and 7p AOs to the t1u MO. This is discussed below.The bonding analysis of the [An(CO)8]−, which correlate with the orbitals in the correlation diagram of Figure 2u orbitals and the a2u MO have some contributions from the 5f AOs of uranium, but the relevance of the 5f‐orbital bonding to the metal–CO bonds is unclear. A quantitative estimate of the contribution of the 5f AOs to the bonding interactions is provided by the EDA‐NOCV method. Table 8]q  by using the metal ion Uq with the given electron configurations and (CO)8 as interacting fragments, which refer to the MO correlation diagram.Figure Eorb contributes 56 % to the total attraction in [U(CO)8]+ and 59 % in [U(CO)8]−. The most important information of the EDA‐NOCV calculations comes from the breakdown of ΔEorb into the pairwise orbital interactions of ΔEorb(1)−ΔEorb(6). The contribution of the [U(d)]+→(CO)8 π backdonation and [U(d)]+←(CO)8 σ donation in the [U(CO)8]+ cation have the same strength; they amount to 64 % of ΔEorb. Not surprisingly, the [U(d)]−→(CO)8 π backdonation in the [U(CO)8]− anion is much stronger than the [U(d)]−←(CO)8 σ donation; both comprise 79 % of the total orbital interactions. Thus, the valence d AOs are the most important metal orbitals in [U(CO)8]q, but the relative contribution to the metal–ligand bonding is smaller than in the late lanthanide octacarbonyl anions [Ln(CO)8]− , in which the metal d‐orbital interactions account for >90 % of the metal‐AO contribution to the covalent bonding.The data in Table q→(CO)8 π backdonation and the [U(f)]q←(CO)8 σ donation contribute 16 % to the total orbital interactions in the cation and in the anion [U(CO)8]q. The data suggest a significant contribution of the metal 5f orbitals to the chemical bonds. The contribution of the 5f AOs to the t1u orbitals, which have mainly 6p character at the metal side, appears to be small. This becomes obvious from the visual inspection of the deformation densities and the associated fragment orbital, which are shown below. The contribution of the uranium 5f AOs to the U−CO bonds in [U(CO)8]q is much higher than that of the 4f AOs of the lanthanide atoms in [Ln(CO)8]− , which amount to <4 % of the Ln−CO bonding orbitals.Eorb values do not only come from genuine orbital interactions between the fragments, they also include intrafragment polarization. A previous study of transition metal hexacarbonyls [TM(CO)6]q  showed that the contribution by polarization is rather small.8]q.Table ρ(1)−Δρ(6), which are associated with the orbital interactions ΔEorb(1)−ΔEorb(6) in [U(CO)8]+ and [U(CO)8]−. Only one component of the degenerate interactions is shown. The color code of the charge flow is red→blue. Note that the plots of the deformation densities of the weaker interactions have smaller isovalues than those of the stronger interactions. The deformation densities nicely show the charge flow that is due to Uq←(CO)8 σ donation into the vacant 6d (t2g) and 5f AOs (a2u) and the reverse Uq→(CO)8 π backdonation from the occupied 6d (eg) and 5f AOs (t2u). Inspection of the deformation density Δρ(6a) (t1u) reveals that the uranium orbital is mainly a 7p AO. The occurrence of a red and a blue area in the deformation density Δρ(6a) of the anion [U(CO)8]− reveals a hybridization 5f/7p at the uranium center during bond formation. Figure ν|, which indicate the size of the charge transfer associated with the respective orbital interactions. Note that the amount of relocated charge does not directly correspond to the energy, because it is also determined by the energy levels of the interaction orbitals.Figure 8]+ and [Th(CO)8]− by using the Dh4 symmetry of the equilibrium structures. They look more complicated than the MO diagram for the hO field of the uranium adducts →eu+a2u(Dh4); t2u(hO)→eu+b2u(Dh4); t2g(hO)→eg+b2g(Dh4). The doubly degenerate orbitals are split as eg(hO)→a1g+b1g(Dh4). Furthermore, a2u(hO)→b1u(Dh4).0 7p0 6d3 5f0 for the doublet state of Th+ in (2A1g) [Th(CO)8]+ and 7s0 7p0 6d4 5f1 for the doublet state of Th− in (2B1u) [Th(CO)8]−. Thus, the irreducible representations of the Dh4 point group make it possible to distinguish between the contributions of the metal valence AOs, except for the 5f and 7p participation in the eu and a2u MOs, which require inspection of the associated deformation densities.Figure s Figure , but the8]+ by using the metal ion Th+ and the (CO)8 cage with the symmetry‐adapted electron configurations 8 interactions possess, like the uranium complexes, a slightly more covalent than electrostatic character. The most important metal AOs in the thorium complex are the 6d orbitals, which have an even higher contribution to the metal–CO bonds than in the uranium complexes. The dominant orbital interactions in the cation [Th(CO)8]+ come from the [Th(d)]+→(CO)8 π backdonation (ΔEorb(1)+ΔEorb(2)) followed by the [Th(d)]+←(CO)8 σ donation (ΔEorb(3)+ΔEorb(4)). The contribution of the metal(6d) AOs to the bonding in [Th(CO)8]+ (75 %) is even higher than in [U(CO)8]+. Inspection of the deformation densities of the eu orbital (ΔEorb(7)) at the metal end shows that it comes mainly from the 5f AOs, whereas the a2u orbital (ΔEorb(8)) comes mainly from the 7p AOs. The total contribution of the metal(5f) AOs in [Th(CO)8]+, which arises from ΔEorb(5) and ΔEorb(7), amounts to ≈10 % and is less than in [U(CO)8]+. The EDA‐NOCV results suggest that the contribution of the dominant pairwise orbital interaction in [Th(CO)8]+ has the same trend as the uranium complexes 6d≫5f>7s≈7p. Figure ρ(1)–(8) that are associated with the interaction energies ΔEorb(1)–(8) in [Th(CO)8]+. They nicely illustrate the charge flow between the metal atom and the ligand orbitals. Only one component of the degenerate orbital is shown.Table 8]− in Table −  and (CO)8, which correspond to the MO correlation diagram in Figure 1u MO and suggests strong [Th(f)]−→(CO)8 π backdonation (ΔEorb(9)). Inspection of the eigenvalues |ν| associated with the deformation densities, which are shown in Figure 8 than at the metal atom. This means that the metal–ligand interactions in [Th(CO)8]− might be better described in terms of interactions between neutral Th and a negatively charged ligand cage (CO)8−, although the bond cleavage gives Th− and 8 CO as fragments.The EDA‐NOCV results for the anion [Th(CO)8]− by using neutral Th, which is in the electronic singlet state and the electron configuration 7s0 6d4 5f0, and (CO)8− as interacting fragments. Previous studies by us suggest that those fragments that give the smallest orbital value ΔEorb are best suited to describe the bond formation, because they undergo the least change by the interatomic interactions.8− as fragments gives a clearly smaller ΔEorb value  than Th−+(CO)8 . Thus, the former EDA‐NOCV calculations provide a more faithful indication of the orbital interactions than the latter. Table 1u MO, which now comes from [Th(f)]←(CO)8− π donation (ΔEorb(9′)), is much weaker than the [Th(f)]−→(CO)8 π backdonation (ΔEorb(9)). The remaining contributions all become a bit larger when Th+(CO)8− are employed as the fragments. The latter EDA‐NOCV calculations of the anion suggest a similar result as for the thorium cation, in other words, there is a dominant contribution of the 6d metal orbitals (84 %), which is larger than in the uranium complex. The contribution of the 5f AOs from the b1u orbitals ΔEorb(5)+ΔEorb(9′) and the eu MO ΔEorb(7), which has mainly 5f character at the metal end, amounts to ≈9 %. The overall relevance of the thorium valence AOs in [Th(CO)8]− has the same trend as the other systems 6d≫5f>7s≈7p.Table ρ(1)–(9′) that are associated with the interaction energies ΔEorb(1)–(9′) in [Th(CO)8]− by using neutral Th  and (CO)8− as interacting fragments. We also show the deformation density Δρ(9) that comes from the fragments Th−  and (CO)8. The remaining deformation densities of the latter fragmentation scheme are shown in Figure S7 (see the Supporting Information); they look very similar to the deformation densities displayed in Figure Figure + is shorter and has a blueshift with respect to the free CO, whereas HOC+ has a longer bond length and the C−O frequency is redshifted. If the σ HOMO of CO would be an antibonding orbital, it should lead to a shorter C−O bond in HCO+ and HOC+. The positive charge attached to the carbon atom in HCO+ makes the C−O bond less polar and more “N2‐like”, which enhances the triple‐bond character, whereas the opposite effect takes in HOC+.It is illuminating to compare the calculated charge transfer with the calculated and experimentally observed redshift of the C−O vibrational frequencies in the metal complexes Table . It is u8]+/−, which come from the eigenvalues of the pairwise orbital interactions that are given in Tables 8]− are strong donors, which agrees with the large redshifts of the adducts 8 are used as fragments, whereas the uranium atom in [U(CO)8]− even carries a positive charge. The actinide atoms in the [An(CO)8]+ cations are charge acceptors, but the overall charge transfer An+←(CO)8 is smaller than in the anions. The effect of the π backdonation in the cations An+→(CO)8 on the C−O stretching frequencies is stronger than the An+←(CO)8 σ donation, but the redshifts in the cations [An(CO)8]+ are much weaker than in the anions [An(CO)8]−. The calculated net charges of the EDA‐NOCV method agree quite well with the values of the Hirshfeld− is an electron acceptor in [U(CO)8]− with a negative charge of −1.33 e. This disagrees with all other values in Table 8]−, which suggests strong U−→(CO)8 π backdonation.Table ts Table . The tho8]+/− carry a negative partial charge, which is at odds with the results of all other methods. It is also difficult to reconcile the NBO charges with the frequency shifts of the carbonyl ligands. The peculiar NBO charges may be caused by the unbalanced treatment of the valence orbitals of the metals in the sequence of orthogonalization steps in the NBO algorithm. The NBO method makes a preselection of those orbitals, which are considered as genuine atomic valence orbitals for the construction of the molecular orbitals. Only those outermost AOs that are occupied in the electronic ground state of the atom are considered as valence AOs, whereas vacant AOs are named Rydberg AOs. Valence AOs were then favored over Rydberg AOs in the NBO algorithm, which yields MOs that are biased towards the chosen AOs. This can lead to curious and inept results, because atoms may sometimes use AOs for chemical bonding that are vacant in the electronic ground state. Some examples were recently reported by us.8]+/−.The NBO method suggests that all metal atoms in the cations and anions [An(CO)8]+ agree quite well with the previous study by Duncan and co‐workersDd4 equilibrium geometry and a redshift of the C−O stretching mode by 80 cm−1. Our calculations give an hO structure and a smaller redshift of 63 cm−1, which agrees better with the experimental value of −56 cm−1 in our work and the observed data of −63 cm−1 by Duncan and co‐workers.8]+ in their work. The authors carried out CASSCF calculations by stating that the five unpaired electrons “reside primarily in the 5f and 7s orbitals.” [13] This is at odds with our results, which give the electron configuration of 7s0 7p0 6d2 5f3 at the uranium atom, in which two unpaired electrons are in 6d AOs. The EDA‐NOCV analysis suggests that the energy contribution through donation from the 6d electrons in the occupied eg AO and the backdonation into the vacant 6d AOs (t2g) are much larger than the contribution of the occupied and vacant 5f AOs (Table 8]+ possesses hO symmetry. We searched for a Dd4 structure with an electron sextet state of [U(CO)8]+ and found an energy minimum structure with the electron configuration of 7s0 7p0 6d1 5f4, which is 24.8 kcal mol−1 higher in energy than the hO structure with the electron configuration of 7s0 7p0 6d2 5f3 . The Dd4 structure exhibits frequency shifts of the C−O stretching mode of 80 and 85 cm−1 , which agrees with the reported value of 80 cm−1 by Duncan and co‐workers.hO structure is in better agreement with the experimental values and clearly lower in energy than the Dd4 structure, we think that the computed Dd4 structure of [U(CO)8]+ in the previous work refers to an excited sextet state of the molecule.Our experimental results for [U(CO)bitals.”  This is 8]+. Ricks et al. interpreted the redshift in terms of U+(5f)→CO π backdonation by saying that “apparently, back‐donation from f orbitals is also quite efficient, even though the spatial overlap is quite different from that of d orbitals.”+→CO π backdonation comes from the two electrons in the 6d AOs. This is in agreement with previous theoretical studies on multiple bonds in terminal actinide complexes LnAn≡E , which suggest that the 6d orbitals of the actinides are more important for chemical bonding than the 5f orbitals.The choice of the electron configuration of the uranium atom has a strong effect on the analysis of the metal–CO bonds in [U(CO)8]+/−. In the work by Duncan and co‐workers, it was suggested that “the d orbitals in actinides are usually less important in bonding, and therefore, stable actinide systems often have 22 electrons .”8H8)2 and other stable actinide complexes in future studies.A final word shall be devoted to the 32‐electron rule,8]+/−  were prepared in the gas phase, and they were studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and the anions were characterized as saturated coordinated complexes. Quantum chemical calculations that used density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (Dh4) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (hO) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8]  and [U(CO)8]  have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method revealed that, along with the dominant 6d valence orbitals, there is significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important that the 5f orbitals of thorium.The octacarbonyl cation and anion complexes of actinide metals [An(CO)The authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


Iron aluminides are still deeply investigated materials for their use in power plants, automotive and chemical industry, and other sectors. This paper shows that it is possible to strongly improve their oxidation behavior by the addition of silicon. The description of the synergic effect of aluminum and silicon on the oxidation behavior of Fe–Al–Si alloys at 800 °C in air is presented. The oxidation rate, microstructure, phase, and chemical composition of these ternary alloys are compared with the binary Fe–Al and Fe–Si alloys. Results showed that the oxidation of Fe–Al–Si ternary alloys provides an oxide layer based on aluminum oxide with a low concentration of iron and silicon. Below this oxide layer, there is a layer of silicides formed as a result of depletion by aluminum, which forms a secondary oxidation protection. On the other hand, Fe2O3 and SiO2 were detected as the oxidation products of Fe–Si alloy by the means of XRD analysis. Both Fe–Al–Si alloys form Al2O3 (cubic γ-Al2O3 modification) and Fe2O3 during the oxidation at 800 °C. In addition, SiO2 was also detected on the surface of FeAl20Si20 alloy. In the case of all tested alloys, the components of the basic material  were also detected due to the low thickness of the oxide scales. However, the Fe3Al2Si3 ternary phase was not detected, even though it is one of the main constituents of the FeAl20Si20 alloy before oxidation, as seen in XRD analysis of the oxidized samples  revealedThe oxide layer on FeAl32 alloy is dense and compact, having the thickness between 2 and 4 µm after the oxidation for 300 h a, dependThe chemical analysis of the oxide layers by EDS  revealedThe EDS chemical analysis was also used in order to describe the changes in chemical composition below the oxide layer. In the case of Fe–Al alloy, strong depletion by aluminum can be seen below the oxide layer . In the GDOES analysis of the oxide layers  confirmeThe presented results showed that the addition of silicon to Fe–Al-based alloys leads to a significant improvement in high-temperature oxidation resistance. A quite surprising fact is that the improvement is almost independent of the ratio between silicon and aluminum. When comparing the oxidation behavior of all tested alloys, we can formulate the following statements.2O3, which is known to have a lower protective effect than α-Al2O3, which forms at higher temperatures (around 1000 °C) [2O3.Fe–Al and Fe–Al–Si alloys tend to form the oxide layer based on aluminum oxide due to a high thermodynamic stability of this oxide . At 800 1000 °C) . Despite2O3) and silicon oxide (SiO2) on the inner side of the oxide layer. The presence of both oxides in significant amounts corresponds well with the similar thermodynamic stability of these oxides  was applied:−1), A is the area of exposed surface (cm2), ρ is the density of oxide (3.95 g.cm−3 for Al2O3 and 5.24 g.cm−3 for Fe2O3), and M(oxide) is the molar weight of oxide (102 g.mol−1 for Al2O3 and 160 g.mol−1 for Fe2O3). The results of the calculation are presented in For comparison purposes, the thickness of the oxide layers was calculated from the weight gains, assuming that the oxidation product is AlFe–Al and Fe–Al–Si alloys form the oxide layer based on aluminum oxide with minor amounts of silicon and aluminum.Fe–Si alloy oxidizes forming the mixture of iron oxide and silicon oxide.The oxidation rate of Fe–Al–Si alloys is three to four orders lower than that of Fe–Al and Fe–Si alloys due to the presence of dense aluminum oxide layer and a layer of iron silicides below it, which act as a secondary oxidation protection.In this paper, the oxidation behavior of Fe–Al, Fe–Si and Fe–Al–Si alloys prepared by mechanical alloying and spark plasma sintering was studied and compared with the following main results: