Divalent State Research Articles

Masked Divalent Reactivity of Heterobimetallic Lanthanide Isocarbonyl Complexes.

A new rare-earth reduction system is described in which trivalent yttrium and dysprosium react as though present in their unstable divalent oxidation state. This masked divalent reactivity is achieved using the isocarbonyl-bridged dimers [(Cpttt2M)(μ-Fp)]2 (M = Y, 1Y; M = Dy, 1Dy; Cpttt = 1,2,4-C5tBu3H2; Fp = CpFe(CO)2), where the reducing electrons originate from the bridging [Fp]- ligands. The reactivity of 1Y and 1Dy is showcased by reducing the N-heterocycles 2,2'-bipyridyl (bipy), phenazine (phnz) and hexaazatrinaphthylene (HAN) to give corresponding mono-, di- and tri-metallic rare-earth complexes, respectively, with the heterocyclic ligands present in their singly, doubly and triply reduced forms, respectively. The dynamic magnetic properties of the dysprosium compounds are described. Compound 1Dy is a single-molecule magnet (SMM) with an appreciable energy barrier of 449(17) cm-1, whereas [(Cpttt2Dy)2(m-phnz)] (3Dy) is not an SMM because of a strong, competing equatorial crystal field. Surprisingly, [(Cpttt2Dy)3(HAN)] (4Dy) is also not an SMM, the origins of which are traced to the impact of the tert-butyl substituents on the dysprosium centre and its interaction with the radical [HAN]3- ligand.

Masked Divalent Reactivity of Heterobimetallic Lanthanide Isocarbonyl Complexes

A new rare‐earth reduction system is described in which trivalent yttrium and dysprosium react as though present in their unstable divalent oxidation state. This masked divalent reactivity is achieved using the isocarbonyl‐bridged dimers [(Cpttt2M)(μ‐Fp)]2 (M = Y, 1Y; M = Dy, 1Dy; Cpttt = 1,2,4‐C5tBu3H2; Fp = CpFe(CO)2), where the reducing electrons originate from the bridging [Fp]– ligands. The reactivity of 1Y and 1Dy is showcased by reducing the N‐heterocycles 2,2'‐bipyridyl (bipy), phenazine (phnz) and hexaazatrinaphthylene (HAN) to give corresponding mono‐, di‐ and tri‐metallic rare‐earth complexes, respectively, with the heterocyclic ligands present in their singly, doubly and triply reduced forms, respectively. The dynamic magnetic properties of the dysprosium compounds are described. Compound 1Dy is a single‐molecule magnet (SMM) with an appreciable energy barrier of 449(17) cm–1, whereas [(Cpttt2Dy)2(m‐phnz)] (3Dy) is not an SMM because of a strong, competing equatorial crystal field. Surprisingly, [(Cpttt2Dy)3(HAN)] (4Dy) is also not an SMM, the origins of which are traced to the impact of the tert‐butyl substituents on the dysprosium centre and its interaction with the radical [HAN]3– ligand.

Visible Light-Sensitive Sustainable Quantum Dot Crystals of Co/Mg Doped Natural Hydroxyapatite Possessing Antimicrobial Activity and Biocompatibility.

Cutting-edge research in advanced materials is increasingly turning toward the development of novel multifunctional nanomaterials for use in high-tech applications. This research uses the solid-state method as a solvent-free technique to create multifunctional quantum dot (QD) hydroxyapatite (HA) crystals from bovine bone waste. By incorporating cobalt (Co) and magnesium (Mg) into the HA structure, the crystallinity of the hexagonal HA nanoparticles (99.7%), showing QD crystals is enhanced. Oxygen vacancies on the surfaces of the HA nanoparticles contributed to their bandgap falling within the visible light range. In addition, the dopants substituted calcium in the HA crystal structure and generated a divalent oxidation state, shifting the bandgap of natural HA toward red wavelengths (3.26 to 1.94eV). Moreover, the incorporation of Co led to magnetization within the HA structure through spin polarization. Additionally, the doped QD crystals of HA nanoparticles showed significant antimicrobial activity against Escherichia coli, Staphylococcus aureus, and bacteriophages MS2, particularly under visible light exposure. In short, the Co/Mg co-doped HA nanoparticles exhibited ferromagnetic properties, sensitivity to visible light, biocompatibility, and considerable antimicrobial effects, establishing their potential as sustainable multifunctional materials for biomedical applications, especially in anti-infection treatments.

Oxidation and ablation resistance of (TiZrHf)C medium-entropy ceramic coating on C/C composite constructed in-situ at low temperature down to 900°C

The low-cost construction of ultra-high temperature high/medium-entropy ceramic coatings is pivotal for advancing their engineering applications. The study successfully prepared (TiZrHf)C medium-entropy ceramic coatings on C/C composite surfaces using an in-situ molten salt disproportionation reaction at temperatures as low as 900°C. The (TiZrHf)C coatings, approximately 20 μm thick, showed uniform distribution of Ti, Zr, and Hf, typical of medium-entropy ceramics. The process entails Hf reducing Zr⁴⁺ and Ti⁴⁺ to divalent states, which then disproportionate and react with carbon to form the coatings. High-temperature oxidation tests revealed larger oxide grain sizes and dense boundaries in coatings with higher Ti content, indicating superior oxidation resistance. Additionally, ablation tests demonstrated that a suitable amount of liquid-phase TiO₂ formed on the composite surface improves ablation resistance by stabilizing the oxide layer. This cost-effective, highly designable method promotes medium/high-entropy ultra-high temperature ceramics' engineering application.

Catalytic Effect of Titanium Ions on the Cathodic Reduction of Selenium (VI), Copper (II), Uranium (VI) Ions and Other Metals in an Aqueous Solutions

It is known that catalytic processes are widely applied in the field of organic chemistry; however they also play a significant role in inorganic chemistry. Nonetheless, numerous unresolved issues persist in the technology of inorganic substances and the extraction of metals and nonmetals in their elemental states. This publication aims to consolidate the results of our pioneering research utilizing the redox Ti (IV)–Ti (III) system, which demonstrates a catalytic action on the cathodic reduction of selenium (VI), copper (II), platinum (IV), palladium (IV), bismuth, arsenic (V) ions, uranium (VI), as well as manganese dioxide suspension. It has been demonstrated that in the presence of the redox Ti (IV)–Ti (III) system, hard-to-reduce selenate ions can be reduced at room temperature. The catalytic action of the redox Ti (IV)–Ti (III) system has been reliably demonstrated, and the reaction mechanism has been established. In the electrochemical production of metal powders (Cu, Pt, Pd, Bi) at cathode current densities exceeding the limiting value, a portion of the current is irreversibly lost to the discharge of hydrogen ions. Consequently, the current efficiency (CE) for powder production does not exceed 80 %. We have established that in the presence of titanium (IV) ions, due to their catalytic action, the CE increases by more than 15 %. It has also been shown that during the cathodic polarization of hexavalent uranium its reduction to uranium (IV) in the presence of the catalyst increases by more than 50 %. The reduction of hard-to-reduce arsenate ions in the presence of titanium (IV) ions proceeds with high CE to the active trivalent state, and further reduction can proceed electrochemically. The cathodic reduction of a manganese dioxide suspension was investigated. In the presence of a catalyst — titanium (IV) ions, manganese in this dioxide is reduced to the divalent state with a current efficiency exceeding 90 %.

Weak antilocalization in the topological semimetal candidate YbAuSb

We report a study of the magnetic and magnetotransport properties of YbAuSb single crystals, which were grown using the bismuth flux. The x-ray diffraction data indicate that YbAuSb crystallizes in LiGaGe-type hexagonal structure with space groupP63mc. Our magnetic measurements revealed that YbAuSb is nonmagnetic with a divalent state of ytterbium ion. The temperature-dependent electrical resistivity exhibits a metallic behavior. A cusp-like feature in transverse and longitudinal magnetoresistance is observed at the low field regime. This cusp-like feature is attributed to the weak antilocalization (WAL) effect, which is more prominent at low temperatures. The transverse magnetoconductivity in low field region follows semiclassical model∼B, which is consistent with the presence of WAL phenomena. The WAL effect in transverse and longitudinal magnetoconductance is well explained using the modified Hikami-Larkin-Nagaoka and generalized Altshuler-Aronov model, respectively. The Hall resistivity shows a linear field dependence with a positive slope, suggesting hole charge carriers dominate in electrical transport. The calculated carrier density and mobility are in the order of 1020 cm-3and 102 cm2 V-1 s-1, respectively.

Three-Dimensional (3D) Porous Reduced Graphene Oxide Aerogel (RGA) Nanoelectrodes Consisted of Palladium Nanoparticles Embedded in Polyethlyenimine (PEI) for Detection of Bisphenol A and H2O2

This research focuses on the development of three-dimensional (3D), hierarchically porous nanoelectrodes, which incorporate palladium nanoparticles within a polyethyleneimine-reduced graphene oxide aerogel (RGA-PEI-Pd). These nanoelectrodes are designed for sensitive detection of bisphenol A (BPA) and hydrogen peroxide (H2O2). The abundant positive charges in polyethyleneimine (PEI) facilitate the formation of a 3D porous structure by connecting to the reduced graphene oxide through carbon-nitrogen bonds, while also anchoring palladium nanoparticles uniformly across the aerogel. This structure maintains the aerogel's porosity.Palladium in its zero-valent (Pd0) and divalent (Pd2+) states plays a crucial role in the catalyst's performance, undergoing redox reactions to alternate between Pd2+ and Pd4+ states. This dynamic contributes to the electrode's ability to effectively oxidize BPA and reduce H2O2. The modified electrode showed low detection limits for BPA (25.5 nM) and H2O2 (16.2 nM) under optimal conditions. Extensive analytical methods, including electrochemical spectroscopy, were employed to delve into the unique electrocatalytic properties of these electrodes.The practical applicability of these electrodes was further demonstrated by their successful use in real-world environmental and biological samples, such as BPA-contaminated water from rivers and lakes, and clinical samples containing MCF-7 cells. The electrodes also exhibited impressive reusability, with recovery rates ranging from 96% to 104.3%.

A Sustainable Process for Rare Earth Electrowinning in Chloride Based Molten Salts

Neodymium production has become increasingly important due to use of neodymium–iron–boron (NdFeB) magnets in green energy, consumer technology and defense applications. The state-of-the-art practice features a neodymium fluoride and lithium fluoride molten salt with a consumable carbon anode converting dissolved neodymium oxide and carbon to neodymium metal and CO2.1-2 The anode effect results in PFCs and CO emissions, which make the current neodymium electrowinning process unsustainable.3-4 Some attempts have been made to electrolyze the chloride salt of neodymium to produce chlorine at the anode. Chlorine is a value-added product which neither consumes the anode nor produces other deleterious GHGs. Additionally, the chloride of neodymium can be non-carbothermically produced through a spontaneous reaction with hydrochloric acid, producing only water as a side product. However, a common problem in chloride rare earth electrowinning is the low Coulombic efficiency (10-50%) obtained in lab-scale and pilot-scale efforts.5 The neodymium chloride electrolysis process notoriously encounters a two-step reduction producing an intermediate divalent (Nd2+) oxidation state which is stable in the chloride media.6-7 The intermediate neodymium species diffuses away from the cathode leading to Coulombic efficiency loss. Additionally, the kinetics of the chlorine evolution reaction (CER) in chloride molten salts are known to be relatively sluggish, causing significant anodic overpotentials which elevate the specific energy consumption during electrowinning. Furthermore, electrowinning from molten salts often produces spongy or dendritic deposits of metal requiring energy-intensive purification. In this talk, we will address all aforementioned technical hurdles and report on our efforts achieving high Coulombic efficiency (~85%), and compact deposits with superior as-electrowon neodymium metal purity (>99 wt.%). Furthermore, we will report the development of a new anode which catalyzes chlorine evolution, lowering the anodic overpotential considerably during electrolysis at high current densities of practical interest for electrowinning. Specific energy consumption is calculated for some example cases and found to be between 2.1 and 3.5 kWh/kg representing a significant improvement over the conventional oxyfluoride process. Figure 1

Revealing the atomic and electronic mechanism of human manganese superoxide dismutase product inhibition

Human manganese superoxide dismutase (MnSOD) is a crucial oxidoreductase that maintains the vitality of mitochondria by converting superoxide (O2●−) to molecular oxygen (O2) and hydrogen peroxide (H2O2) with proton-coupled electron transfers (PCETs). Human MnSOD has evolved to be highly product inhibited to limit the formation of H2O2, a freely diffusible oxidant and signaling molecule. The product-inhibited complex is thought to be composed of a peroxide (O22−) or hydroperoxide (HO2−) species bound to Mn ion and formed from an unknown PCET mechanism. PCET mechanisms of proteins are typically not known due to difficulties in detecting the protonation states of specific residues that coincide with the electronic state of the redox center. To shed light on the mechanism, we combine neutron diffraction and X-ray absorption spectroscopy of the product-bound, trivalent, and divalent states of the enzyme to reveal the positions of all the atoms, including hydrogen, and the electronic configuration of the metal ion. The data identifies the product-inhibited complex, and a PCET mechanism of inhibition is constructed.

Jahn-Teller effect and features of divalent copper ion behavior in multicomponent borate crystals

Crystals of YGa3(BO3)4, YAl3(BO3)4, EuGa3(BO3)4 and EuAl3(BO3)4 with copper alloy were studied by electron paramagnetic resonance and X-ray diffraction analysis. The lattice parameters and coordinates of copper-doped boron atoms were determined. The study of EPR spectra showed that copper is in the divalent state and replaces aluminum ions with C2 node symmetry. In YAl3(BO3)4:Cu crystals, a ligand structure exists due to the interaction of copper electrons with yttrium nuclei. The parameters of the spin Hamiltonian describing the behavior of the Cu2+ spectrum have been determined. The deviation of the Z-axis spectra from the C3 axis by 54(1)° is due to Jahn-Teller vibronic interaction and monoclinic distortion. In the EuGa3(BO3)4 crystal, a new spectrum 2 was found, which also belongs to divalent copper but is observed at an excited state 31 cm−1 away from the ground state. Above 70 K, an isotropic EPR line with a width of 450 Gs, g = 2.1, appears and exists up to room temperature.

Tourmaline as a petrogenetic indicator highlighted in a multicoloured crystal from the gem deposit of Mavuco, Alto Ligoña pegmatite district, NE Mozambique

Abstract A rounded fragment of a multicoloured tourmaline crystal (2.5 cm diameter), collected from the secondary gem deposit of Mavuco, Alto Ligoña pegmatite district, Mozambique, has been investigated using a multi-analytical approach, with the objective of reconstructing its growth history. The sample represents a core-to-rim section, perpendicular to the c axis, of a crystal characterised by a variety of colours. These change from a black core to an intermediate zone with a series of colours, yellow, blue–green and purple, to a final dark-green prismatic overgrowth. These changes are the result of a wide variation in Fe, Mn, Ti and Cu concentrations and their redox state. The black core is characterised by enrichment in Fe and Mn, with iron present in its divalent state. The yellow zone shows a progressive depletion in Fe and its colouration is caused by Mn2+ and Mn2+-Ti4+ IVCT interactions. The progressive decrease in Mn coupled with the absence of Ti, and the lack of Fe, implies that Cu2+ acts as the only chromophore in the pale blue–green zone. The dominant colour-causing agent of the purplish zone is Mn3+, denoting a change in redox environment; however, even though the amount of Cu remains significant, its chromophore effect is obscured by Mn3+. The dark-green prismatic overgrowth, characterised by a sharp increase in Fe, Mn and also Ca, is interpreted as a late-stage partial re-opening of the geochemical system. This occurrence could potentially be related to mechanical instability of the cavity in which the crystal grew.

Unveiling the transformation of 2,4,6-trihalophenols by active species in drinking water pipelines: The role of goethite

The long-term accumulated pipe scale in the water distribution system (WDS) is vital for ensuring the safety of drinking water delivery. This study revealed a novel positive role of pipe scale in triggering interface free radicals for aromatic substances degradation. The goethite (main constituents of pipe scale) converts from the trivalent state to the divalent state by withdraw electrons from aromatic phenolic compounds. Active free radicals such as hydroxyl radical (OH), Cl, and ClO were subsequently formed via a cascade of chain reactions under WDS conditions, among which OH was the dominate active species driving efficient transformation of 2,4,6-trichlorophenol (60.8%) and 2,4,6-tribromophenol (80.5%) and the corresponding toxicity attenuation. The goethite mediated chlorination is a surface reaction following Langmuir–Hinshelwood model. Our works revealed the presence of natural source of OH for disinfection byproducts transformation. Given the ubiquitous existence of iron scales inside ductile iron pipe, the finding renewed the understanding of the impact of WDS on drinking water quality.

Low-temperature aqueous synthesis and biocompatibility of manganese whitlockite

In this work, manganese whitlockite (Mn-WH, Ca18Mn2(HPO4)2(PO4)12) was successfully synthesized and comprehensively characterized. This material is a manganese-containing analog of the biomineral magnesium whitlockite (Mg-WH, Ca18Mg2(HPO4)2(PO4)12). The synthesis was performed via a low-temperature dissolution-precipitation process in aqueous medium under ambient pressure at 75 °C using dicalcium phosphate dehydrate and manganese acetate tetrahydrate as starting materials. The crystal structure of the synthesized powder was determined by powder X-ray diffraction, FTIR and Raman spectroscopies, demonstrating the presence of characteristic structural units. Morphological features and elemental distribution within the synthesized powder were studied by SEM/EDX analysis. XPS, EPR and magnetic studies confirmed the presence of Mn ions in a divalent state. Temperature-dependent magnetic measurements revealed a paramagnetic behavior of Mn-WH down to 5 K. In vitro cytotoxicity experiments were performed with MC3T3-E1 preosteoblastic cell line.

A model of ionization-induced reactions in CH4/N2 clusters in Titan's atmosphere: theoretical insights into mono- and divalent states

Abstract We propose a model for ionization-induced reactions between N2 and CH4, the main components of Titan's atmosphere, and examine their mechanism using quantum mechanical and molecular dynamics methods. Bimolecular CH4–N2 clusters form through collision, and their conformation depends on the encounter cross section due to weak intermolecular interaction. These clusters acquire a driving force through vertical ionization because the vertically ionized structure is not situated at the minimum of the potential energy surface in the ionized state. This leads to multiple reactions, overcoming energy barriers in the process. In the divalent state, a robust attractive interaction occurs between CH4 and N2 through charge transfer. Subsequently, the H4C–N2 covalent bond forms prior to reactions, resulting in the production of N2H+, CH3+, CH3N2+, and CH2N2+; otherwise only N2H+, CH3+, and CH2+ are generated. In contrast, when ionized to a monovalent state, although dissociation of N2H+ and isomerization to CH3NHN+ and CH3NNH+ occurs, a significant portion dissociates into CH4+ and N2 without undergoing further reactions. Additionally, the generation of N2H+ and CH3+ is limited in the monovalent state, primarily due to a lower driving force and the absence of Coulombic explosion. Our computational results highlight the pivotal role of divalent reactions within Titan's atmosphere, which are more efficient than monovalent reactions.

Defects assisted the enhancement of optical and ferromagnetism in Zn1-xCoxS quantum dots: Toward efficient optoelectronic and spintronic applications

Colloidal Co-doped ZnS Quantum dots (QDs) were successfully synthesized through a facile and effective chemical co-precipitation method using polyethylene glycol (PEG) as a capping agent. A comprehensive study on the structure, optoelectronic, and magnetic properties of ZnS: Co2+ QDs was thoroughly carried out using diverse characterization techniques. Transmission electron micrographs reveal spherical QDs with a mean particle size of 5 ± 0.5 nm, whereas the X-ray diffraction (XRD) analysis and Raman spectroscopy confirm the exclusive presence of cubic ZnS phase structure, without any signs of Co-related impurity phases. Energy-dispersive x-ray (EDX) analysis verifies the presence of only three elements: Zinc, Cobalt, and Sulphur, with nearly stoichiometric proportions. X-ray photoemission (XPS) analysis confirmed the presence of Co2+ ions in the divalent oxidation state as well as the fair existence of sulphur vacancies. Optical measurements demonstrate that Co-doping in ZnS leads to a decrease in the optical band gap owing to the presence of defects that create localized states within the band structure. In addition, the refractive index (n) is found to increase with Co-doping level due to the increase in the polarizability. The outcomes of optical properties reveal that the tunability of the optical band gap and dispersive oscillator parameters in Co-doped ZnS QDs results in an enhancement of the non-linear optical parameters, such as third-order non-linear optical susceptibility χ(3), and non-linear refractive index n2, rendering them well-suited for applications in optoelectronic devices. Furthermore, the room-temperature photoluminescence (PL) spectra revealed that the Co-doped ZnS QDs have two broad emission bands, including the blue emission, and the green emission. By varying the level of Co-doping, it becomes possible to effectively control the relative PL intensities of dual-color emissions, highlighting their potential for producing adjustable color outputs. The room temperature ferromagnetic behaviour of the QDs has been observed and analyzed in accordance with the bound magnetic polarons model. These findings suggest that Co-doped ZnS QDs can be utilized effectively in the design of spintronic devices.

Slow magnetic relaxation in a europium(II) complex.

Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) EuII complex, the [EuII(N{SiMePh2}2)2] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures.

Photoinduced electron transfer in Eu2+ and Sm3+ co-doped CaF2 nanocrystals prepared by co-precipitation

We report on the photoinduced electron transfer in Eu2+ and Sm3+ co-doped CaF2 nanocrystals prepared by a facile co-precipitation method using CaCl2, EuCl2, SmCl3 and NH4F. The doping of divalent Eu2+ was realized by employing granular zinc in the CaCl2/EuCl2 solution under nitrogen to reduce Eu3+→ Eu2+. The CaF2:xEu,0.2%Sm nanocrystals were prepared with different Eu concentrations of x = 0, 0.2, 0.5, 1.5, and 2.5%, resulting in an average crystallite size between 54 and 36 ± 1 nm. The maximum luminescence intensities of Eu2+ and Sm2+ were obtained for the x = 0.5% sample. Photoinduced electron transfer and back transfer in the CaF2:0.5%Eu,0.2%Sm nanocrystals were measured by detecting the Eu2+ and Sm2+ luminescence, upon exposure to 340 and 310 nm UV LED light. Interestingly, the photoionization of Eu2+ occurred 6 times faster for the sample co-doped with 0.2% Sm. Upon exposure to 340 nm light, a reduction and increase of the Eu2+ and the Sm2+ luminescence were observed, respectively. Subsequent exposure to 310 nm light decreased the Sm2+ luminescence, but the luminescence of Eu2+ kept on being bleached, albeit at a lower rate. Whilst the Sm valence state could be reversibly changed between the trivalent and divalent state by 340 and 310 nm light, the observation that the Eu2+ luminescence did not recover may indicate that a third centre is involved in the photoinduced electron transfer mechanisms.

Kinetics of electrochemical Eu3+ to Eu2+ reduction in aqueous media

All lanthanides have a stable trivalent oxidation state, but some of them can also occur in the divalent or tetravalent state. Europium is well-known for its divalent oxidation state, which has been investigated in aqueous, organic, and molten salt media. In contrast to other lanthanides, Eu3+ can be easily reduced (Eo=−0.34 V vs. SHE) via chemical, electrochemical or photochemical routes, and Eu2+ is quite stable in a variety of electrolytes, including nitrate salts. To date, the kinetics of the Eu3+/Eu2+ reduction reaction has been investigated only by polarography and chronopotentiometry, most often in perchlorate medium. In this study, the kinetics of the Eu3+/Eu2+ couple were analysed in nitrate, chloride and perchlorate media by cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE). The diffusion coefficient, charge transfer coefficient and rate constants were calculated based on the Levich and Koutecký-Levich analysis and Tafel plot to gain insight in the electrochemical process and the influence of the electrolyte type on it. Given the pre-existing characterization of this redox couple in perchlorate medium, it is selected as a reference system to both compare the kinetic parameters and to validate whether the methodology can be applied to other electrolytes. The Eu3+ reduction reaction was found to be quasi-reversible in these electrolytes and the calculated kinetic parameters are in line with the previously reported values.

Alkaline Earth Metal Superatom of W@Si16: Characterization of Group 6 Metal Encapsulating Si16 Cage on Organic Substrates.

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si16) exhibit a superatomic nature, depending on the central M atom owing to the number of valence electrons and charge state on organic substrates. Since M@Si16 superatom featuring group 4 and 5 transition metal atoms exhibit rare-gas-like and alkali-like characteristics, respectively, group 6 transition metal atoms are expected to show alkaline earth-like behavior. In this study, M@Si16, comprising a central atom from group 6 (MVI = Cr, Mo, and W) were deposited on C60 substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures. In comparison to alkali-like Ta@Si16, the extent of charge transfer to the C60 substrate is approximately doubled, while the oxidative reactivity is subdued for MVI@Si16 on C60, especially for W@Si16. The results show that a divalent state of MVI@Si162+ appears on the C60 substrate, which is consistently calculated to be a symmetrical cage structure of W@Si162+ in C3v, revealing insights into the "periodic law" of M@Si16 superatoms pertaining to the characteristics of alkaline earth metals.

Mixing entropy and enthalpy effects on europium ions in Eu-doped BaAl2O4

Distributions of Eu2+ and Eu3+ do affect the optical properties. However, the substitution of the activator ions hardly perturbed the crystal structure of the host lattice. Without the differences in crystal structure, it is not trivial to develop an effective descriptor to investigate stoichiometry-dependent mechanism to explore the effects of Eu species on valence states. In this study, through x-ray nanodiffraction, x-ray fluorescence, x-ray absorption near edge structure, and x-ray excited optical luminescence, we mapped the valence state distributions of Eu species to calculate the local mixing enthalpy and entropy. The calculated thermodynamics parameters show good agreement with the optical properties. We found that Eu2+ of Eu-doped BaAl2O4 predominantly existed in a divalent state, which results in segregation phenomena of local Eu2+ and Eu3+ ions.