Crystal Field Stabilization Energy Research Articles

Effect of Metal d Band Position on Anion Redox in Alkali-Rich Sulfides.

New energy storage methods are emerging to increase the energy density of state-of-the-art battery systems beyond conventional intercalation electrode materials. For instance, employing anion redox can yield higher capacities compared with transition metal redox alone. Anion redox in sulfides has been recognized since the early days of rechargeable battery research. Here, we study the effect of d-p overlap in controlling anion redox by shifting the metal d band position relative to the S p band. We aim to determine the effect of shifting the d band position on the electronic structure and, ultimately, on charge compensation. Two isostructural sulfides LiNaFeS2 and LiNaCoS2 are directly compared to the hypothesis that the Co material should yield more covalent metal-anion bonds. LiNaCoS2 exhibits a multielectron capacity of ≥1.7 electrons per formula unit, but despite the lowered Co d band, the voltage of anion redox is close to that of LiNaFeS2. Interestingly, the material suffers from rapid capacity fade. Through a combination of solid-state nuclear magnetic resonance spectroscopy, Co and S X-ray absorption spectroscopy, X-ray diffraction, and partial density of states calculations, we demonstrate that oxidation of S nonbonding p states to S2 2- occurs in early states of charge, which leads to an irreversible phase transition. We conclude that the lower energy of Co d bands increases their overlap with S p bands while maintaining S nonbonding p states at the same higher energy level, thus causing no alteration in the oxidation potential. Further, the higher crystal field stabilization energy for octahedral coordination over tetrahedral coordination is proposed to cause the irreversible phase transition in LiNaCoS2.

Strategic Atomic Interaction Modification for Highly Durable Inorganic Solid Electrolytes in Advanced All‐Solid‐State Li‐Metal Batteries

All‐solid‐state Li‐metal battery (ASSLB) represents advantageous energy storage system for automotive applications. For ASSLB, inorganic solid electrolyte is essential in determining safety and cycling performance. However, significant challenges persist in practical construction of ASSLB with optimized electrolyte. Specifically, electrolyte's structural instability influencing its electrochemical performance remains critical issue within typical operating temperatures for ASSLB in electric vehicles. Herein, this challenge is fundamentally addressed by substituting trace amount of lithium with cadmium, which lacks crystal field stabilization energy. This strategy of atomic interaction modification has induced electrolyte's structural distortion and electronic alteration by deliberately introducing disorder at local lithium sites. Li symmetric cell with cadmium‐substituted antiperovskite solid electrolyte exhibits outstanding critical current density of 11.5 mA cm−2 (5.75 mAh cm−2) and excellent stability for 3000 h at 10.0 mA cm−2 (5.0 mAh cm−2). This study highlights explicit research direction for breakthrough of ASSLB, focusing on understanding how local distortion affects complex inorganic materials.

Engineering Single-Atom Sites with the Irving-Williams Series for the Simultaneous Co-photocatalytic CO2 Reduction and CH3CHO Oxidation.

The bonding effects between 3d transition-metal single sites and supports originate from crystal field stabilization energy (CFSE). The 3d transition-metal atoms of the spontaneous geometrical distortions, that is the Jahn-Teller effect, can alter CFSE, thereby leading to the Irving-Williams series. However, engineering single-atom sites (SASs) using the Irving-Williams series as an ideal guideline has not been reported to date. Herein, alkynyl-linked covalent phenanthroline frameworks (CPFs) with phenanthroline units are developed to anchor the desired 3d single metal ions from d5 to d10 (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+). The Irving-Williams series was employed to accurately predict the bonding effects between 3d transition-metal atoms and phenanthroline units. To verify this, theoretical calculations and experimental results reveal that Cu-SASs/CPFs exhibits higher stability and faster charge-transfer efficiency, far surpassing other metal-SASs/CPFs. As expected, Cu-SASs/CPFs demonstrates a high photoreduction of CO2-to-CO activity (~30.3 μmol·g-1·h-1) and an exceptional photooxidation of CH3CHO-to-CH3COOH activity (~24.7 μmol·g-1·h-1). Interestingly, the generated *O2- is derived from the process of CO2 reduction, thereby triggering a CH3CHO oxidation reaction. This work provides a novel design concept for designing SASs by the Irving-Williams to regulate the catalytic performances.

Interface Engineering via Constructing Enhanced Ligand Enables Highly Stable Li‐Rich Layered Oxide Cathode

AbstractHigh‐energy‐density and cost‐effective lithium‐rich oxides (LRO) are considered as the promising cathode materials for the next‐generation lithium‐ion batteries . Nevertheless, the elevated cut‐off voltage and the complex interface interactions have presented significant challenges that can lead to material degradation. Specifically, the inevitable release of lattice oxygen and the highly reactive interface‐driven irreversible migration of transition metal (TM) ions in LRO make the construction of a robust interface extremely important. Herein, an effective and efficient coating approach is applied to stabilize the interface structure of LRO by introducing a coordination bond between the strong ligand of polyurethane (PU) and the surface of LRO particles. This functional coating stabilizes the crystal field stabilization energies of LRO by acting as a strong ligand in spectrochemistry to form a coordination bond with Mn4+ in Li2MnO3 at high voltage. Consequently, irreversible oxygen release and TM ions migration are greatly inhibited. Overall, the LRO‐PU cathode exhibits superior electrochemical cyclability with a retention of 80.0% at 1C after 300 cycles and enhanced rate capability with a retention of 80.9% at 0.1C after rate cycles, marking a significant step toward commercial implementation.

Melt-quenched carboxylate metal–organic framework glasses

Although carboxylate-based frameworks are commonly used architectures in metal-organic frameworks (MOFs), liquid/glass MOFs have thus far mainly been obtained from azole- or weakly coordinating ligand-based frameworks. This is because strong coordination bonds of carboxylate ligands to metals block the thermal vitrification pathways of carboxylate-based MOFs. In this study, we present the example of carboxylate-based melt-quenched MOF glasses comprising Mg2+ or Mn2+ with an aliphatic carboxylate ligand, adipate. These MOFs have a low melting temperature (Tm) of 284 °C and 238 °C, respectively, compared to zeolitic-imidazolate framework (ZIF) glasses, and superior mechanical properties in terms of hardness and elastic modulus. The low Tm may be attributed to the flexibility and low symmetry of the aliphatic carboxylate ligand, which raises the entropy of fusion (ΔSfus), and the lack of crystal field stabilization energy on metal ions, reducing enthalpy of fusion (ΔHfus). This research will serve as a cornerstone for the integration of numerous carboxylate-based MOFs into MOF glasses.

Kinetic partitioning of trace cations between zoned clinopyroxene and a variably cooled-decompressed alkali basalt: Thermodynamic considerations on lattice strain and electrostatic energies of substitution

We present kinetic partitioning data for trace cations measured in zoned clinopyroxene crystals obtained from a variably cooled and decompressed olivine basalt erupted at Mt. Etna volcano in Italy. Supersaturation effects and compositional heterogeneities at the interface melt lead to the development of sector zoning, concentric zoning, and patchy zoning in clinopyroxene crystals. Apparent partition coefficients between compositionally different growth layers and adjacent melts (Di) for isovalent groups of trace elements are tested for internal consistency on the thermodynamic basis of lattice strain (ΔGstrain) and electrostatic (ΔGelec) energies of substitutions. The excess energy of partitioning (ΔGpartitioning) for trace cations in zoned crystals accounts for a kinetic incorporation control leading to large enthalpic effects through distortion of the lattice and changes in the electrostatic forces. ΔGpartitioning depends upon the complementary relationship between ΔGstrain and ΔGelec, which is the most appropriate thermodynamic description for the accommodation of rare earth elements and high field strength elements in the lattice site of zoned crystals. Polyhedral sectors, skeletal forms, and overgrowth zones have Di values settled by the number of charge-balanced and -imbalanced configurations taking place in the lattice site as a function of aluminium in tetrahedral coordination, and crystal structural changes produced by heterovalent cation substitutions. In an energetically unstable macroscopic system ruled by cooling and decompression, thermodynamic requirements for the crystallochemical control of Di encompass the attainment of local equilibrium at the crystal-melt interface via the establishment of small-volume reaction kinetics. The requisite of local interface equilibrium is however susceptible to the anisotropic growth velocity of each specific clinopyroxene surface, thereby giving reason to different energetic properties of the crystallographic site. This axiomatic control requires that transition metal cations partition also in consideration of electronic effects related to the crystal field stabilization energy. The overriding implication is that Di values for trace cations having different size, charge, and electronic configuration serve as sensitive probes of the different crystal growth mechanisms, surface incorporation sites, and arrangements of atoms at the lattice-scale. In this perspective, fractional crystallization modeling of 2011–2013 bulk rock data from lava fountains indicates that the compositional evolution of magmas erupted at Mt. Etna cannot be described by a unique equilibrium value of Di for a given clinopyroxene-melt interface. The leverage of interface kinetics is distinctively dominant along the subvolcanic plumbing system, thereby requiring that values of Di differ for structurally and compositionally distinct zones in clinopyroxene phenocrysts. To successfully interpret the trace element signature of Etnean magmas, the archetypal constancy of partition coefficient at bulk thermodynamic equilibrium must be in some measure reappraised in favor of the establishment of a local interface equilibrium upon highly dynamic crystallization and growth conditions.

Structural analysis and polarization study of CoCr2O4 nanoparticles

We present the room temperature polarization study of the multiferroic compound CoCr2O4. The co-existence of two elements (Co and Cr) in partially filled d-blocks makes these compounds exhibit a wide range of physical properties. The Cr3+ions almost invariably cover the octahedral (Oh) sites as the crystal field stabilization energy (CFSE) is more than 224 kJ mol −1. The chemical based Sol-gel self-combustion method has been used to successfully synthesize CoCr2O4 chromite. Laboratory X-ray diffraction (LXRD) and synchrotron X-ray diffraction (SXRD) investigations approve the single-phase face centered crystalline structure. The obtained space group is Fd3m. The average crystallite size has been determined by Debye Scherrer’s method and the Williamson Hall [W-H] method. The obtained size is found to be ~ 27 and 17 nm respectively, for both methods when the data is measured by SXRD. The scanning electron micrograph (SEM) shows the agglomeration of particles, which is confirmed by surface topography. Room temperature polarization study exposes the weaker strength of ferroelectricity, which is principally due to charge reversal in the CoCr2O4 compound. The experimental value for retaining polarization is found to be ~ 65% at room temperature (300K).

Ligand field regulation of δ-MnO2 by polyanion modification enables extended potential window in supercapacitors

Extending the potential range of MnO2 is imperative to improve power density and capacity density for supercapacitors. However, MnO2 usually suffers from severe Mn dissolution, irreversible phase transition, and poor cycling performance under an extended potential range. Herein, a ligand field regulation strategy is rationally designed to enhance the structural stability of δ-MnO2 to extend the potential window to 0–1.3 V (vs. Ag/AgCl). As revealed, the generated strong covalent B–O plane triangle or P–O tetrahedron configuration effectively decreases the lattice O activity of δ-MnO2. The B–O–Mn and P–O–Mn bonding interactions enhance Mn ion crystal field stabilization energy in the MnO6 octahedra. Therefore, the lattice O loss, Mn dissolution, and irreversible phase transition are well suppressed. The PO43− doped δ-MnO2 electrodes (with a high mass loading of ∼10 mg cm−2) can deliver a large specific capacitance (268.3 F g−1 at 0.5 A g−1) and excellent cycling performance (83.5% after 10000 cycles) in the extended potential window of 0–1.3 V (vs. Ag/AgCl). Our ligand field regulation strategy affords opportunities for developing simultaneously high-capacity and high-voltage electrodes for supercapacitors.

Sustainable Cellulose Nanofibers-Mediated Synthesis of Uniform Spinel Zn-Ferrites Nanocorals for High Performances in Supercapacitors.

Spinel ferrites are versatile, low-cost, and abundant metal oxides with remarkable electronic and magnetic properties, which find several applications. Among them, they have been considered part of the next generation of electrochemical energy storage materials due to their variable oxidation states, low environmental toxicity, and possible synthesis through simple green chemical processing. However, most traditional procedures lead to the formation of poorly controlled materials (in terms of size, shape, composition, and/or crystalline structure). Thus, we report herein a cellulose nanofibers-mediated green procedure to prepare controlled highly porous nanocorals comprised of spinel Zn-ferrites. Then, they presented remarkable applications as electrodes in supercapacitors, which were thoroughly and critically discussed. The spinel Zn-ferrites nanocorals supercapacitor showed a much higher maximum specific capacitance (2031.81 F g-1 at a current density of 1 A g-1) than Fe2O3 and ZnO counterparts prepared by a similar approach (189.74 and 24.39 F g-1 at a current density of 1 A g-1). Its cyclic stability was also scrutinized via galvanostatic charging/discharging and electrochemical impedance spectroscopy, indicating excellent long-term stability. In addition, we manufactured an asymmetric supercapacitor device, which offered a high energy density value of 18.1 Wh kg-1 at a power density of 2609.2 W kg-1 (at 1 A g-1 in 2.0 mol L-1 KOH electrolyte). Based on our findings, we believe that higher performances observed for spinel Zn-ferrites nanocorals could be explained by their unique crystal structure and electronic configuration based on crystal field stabilization energy, which provides an electrostatic repulsion between the d electrons and the p orbitals of the surrounding oxygen anions, creating a level of energy that determines their final supercapacitance then evidenced, which is a very interesting property that could be explored for the production of clean energy storage devices.

Ion-specific bathochromic shifts: Simultaneous detection of multiple heavy metal pollutants via charge transfer interactions

An anthraimidazoledione-based colorimetric probe (1) has been developed to detect heavy metal pollutants in acetonitrile medium. Adding metal ions, such as Zn2+, Ni2+ and Co2+ induce ion-dependent redshifts in the metal-to-ligand charge transfer (MLCT) band. As a result, the almost colorless solution of1turned into green, yellow and red colors upon adding Zn2+, Ni2+, and Co2+ ions. On the other hand, the blue fluorescence of 1 is slightly quenched in the presence of Zn2+ ions, while the diminution is significant for Ni2+ ions. On the other hand, Co2+ ion results in the red-shift of emission maxima and quenching. Thus, we could observe faint cyan-colored fluorescence with Co2+ ions. The binding affinities for metal ions follow Irving–William’s order. At the same time, the colorimetric responses depend on the ionic radius, hydration enthalpy, coordination number, crystal field stabilization energies of the metal ions, etc. However, in the mixed aqueous environment, the ratiometric response was noticed only with Co2+ ions. Along with ratiometric color change, additions of metal ions result in an increase in both anodic and cathodic peak current along with shifts in the redox potential values. Further, the presence of residual Co2+ was determined in natural water samples.

Mono- and Rare Trinuclear Zn(II) Complexes with Near-Infrared Emissive Ligands: Anion-Responsive Nuclearity Control, Interconversion, Solid-State NIR Emission, and Latent Fingerprint Imaging

The ability to predictably control the nuclearity of metal complexes is vital in developing functional coordination compounds and metal–organic frameworks. However, consistent nuclearity control achieving complexes of different nuclearities using a series of ligands is difficult, especially when the metal ion involved does not show any crystal field stabilization energy for a particular geometry. Herein, a series of three mononuclear (M1–M3) and the corresponding trinuclear (T1–T3) Zn(II) complexes have been synthesized from a series of near-infrared (NIR)-emitting ligands (HL1–HL3) through counterion control (ZnCl2 vs Zn(OAc)2). The structural analyses revealed a regular distorted tetrahedral geometry for the mononuclear complexes, M1–M3. However, the complexes T1–T3 showed a rare trinuclear structure, in which two deprotonated ligand molecules coordinate with three Zn(II) centers such that a central octahedral Zn ion is connected to two terminal tetrahedral Zn ions through phenolate and acetate bridging groups. Intramolecular π–π stacking interactions between the constituting ligands play significant roles in forming such a rare geometry. The plausible reasons for the counterion-controlled nuclearity have been proposed along with successful interconversion of trinuclear complexes to mononuclear complexes at 65 °C. The complexes M1–M3 and T1–T3 exhibited substituent and nuclearity-dependent photophysical properties. In the solid state, two of the mononuclear complexes, M1 and M2, displayed NIR emissions (661–670 nm), while the trinuclear complexes T1–T3 emitted yellow/orange fluorescence (572–607 nm). The complexes M2 and T1 were successfully tested as latent fingerprint (LFP) imaging agents on several non-infiltrating and semi-infiltrating substrates, including everyday household objects, using the powder dusting method. In all these cases, highly fluorescent LFP images with high sensitivity, selectivity, and contrast and low background interference have been obtained.

Comprehensive investigation of crystallographic, spin-electronic and magnetic structure of [formula omitted]: Unraveling the suppression of configuration entropy in high entropy oxides

High entropy oxides (HEOs) are a rapidly emerging class of functional materials consisting of multiple principal cations. The original paradigm of HEOs assumes cationic occupations with the highest possible configurational entropy allowed by the composition and crystallographic structure. However, the fundamental question remains on the actual degree of configurational disorder in HEOs, especially, in systems with low enthalpy barriers for cation anti-site mixing. Considering the experimental limitations due to the presence of multiple principal cations in HEOs, here we utilize a robust and cross-referenced characterization approach using soft X-ray magnetic circular dichroism, hard X-ray absorption spectroscopy, Mössbauer spectroscopy, neutron powder diffraction and SQUID magnetometry to study the competition between crystal field stabilization energy and configurational entropy governing the cation occupation in a spinel HEO (S-HEO), (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4. In contrast to the previous studies, the derived complete structural and spin-electronic model, (Co0.6Fe0.4)(Cr0.3Fe0.1Mn0.3Ni0.3)2O4, highlights a significant deviation from the hitherto assumed paradigm of entropy-driven non-preferential distribution of cations in HEOs. An immediate correlation of this result can be drawn with bulk as well as the local element specific magnetic properties, which are intrinsically dictated by cationic occupations in spinels. The real local lattice picture presented here provides an alternate viewpoint on ionic arrangement in HEOs, which is of fundamental interest for predicting and designing their structure-dependent functionalities.

Elevating the discharge plateau of prussian blue analogs through low-spin Fe redox induced intercalation pseudocapacitance

Low-cost Prussian blue analogs (PBAs) have attracted great attentions as a group of promising cathodes for sodium-ion batteries (SIBs) due to their tailorable and open frameworks which endue the possibility of ultrahigh Na+ diffusion kinetics. Herein, a unique discharging plateau elevation was firstly determined in the iron hexacyanoferrate. The synergy between the crystal field and ligand field stabilization energy in the OH-coordinated Fe sites lowers the activation energy barrier of low-spin Fe, thus inducing the intercalation pseudocapacitance. Furthermore, we prove that the Na+ storage mechanism of high-spin Fe redox reaction features an ion–diffusion behavior while the low-spin Fe redox reaction shows a pseudocapacitance behavior. Benefitting from the improved ionic diffusivity in intercalation pseudocapacitance, the full cell achieves an outstanding rate performance and long-term cycling stability of over 3000 cycles at 500 mA g−1. It is expected that manipulating Fe redox kinetics of the PBAs through inducing special coordinated groups could be a new pathway towards the design of practical high-voltage SIBs.

A Single Crystal Hybrid Ligand Framework of Copper(II) with Stable Intrinsic Blue-Light Luminescence in Aqueous Solution.

Single-crystal solid–liquid dual-phase hybrid organic–inorganic ligand frameworks with reversible sensing response facilitated by external stimuli have received significant attention in recent years. This report presents a significant leap in designing electronic structures that display reversible dual-phase photoluminescence properties from single-crystal hybrid ligand frameworks. Three-dimensional Cu(C3N2H4)4Cl2 complex frameworks were formed through the intermolecular hydrogen bonding and π⋯π stacking supramolecular interactions. The absorption band peaks at 627 nm were assigned to d–d transition showing 10Dq = 15,949 cm−1 and crystal field stabilization energy (CFSE) = 0.6 × 10Dq = 114.4 kJmol−1, while the ligand-to-metal charge transfer (LMCT) of complexes was displayed at 292 nm. The intense luminescence band results from LMCT present at 397 nm. Considering its structure, air stability, framework forming and stable luminescence in aqueous solution, the Cu(C3N2H4)4Cl2 complex shows potential for luminescence Cu-based sensors using emission intensity to detect heavy metal ion species.

Kinetic partitioning of major-minor cations between olivine and Hawaiian tholeiitic basalt under variable undercooling and cooling rate conditions

In order to elucidate the kinetic partitioning of cations between olivine and basalt, we performed undercooling (−ΔT) and cooling rate (CR) experiments at atmospheric pressure and QFM-2 buffer. Starting from the superliquidus temperature of 1250 °C, a Hawaiian tholeiitic basalt was cooled at the rates of 4 (CR4), 20 (CR20), and 60 (CR60) °C/h to the final target temperatures of 1175 °C (−ΔT = 35 °C; −ΔT35) and 1125 °C (−ΔT = 85 °C; −ΔT85). Results show that polyhedral olivine morphologies are obtained at -ΔT35, whereas strong disequilibrium skeletal and/or dendritic textures form at -ΔT85. The amount of forsterite in olivine decreases from to 85% to 78% with increasing both -ΔT and CR. A diffusive boundary layer also develops in the melt next to the olivine surface and its composition becomes progressively enriched in Ca, owing to its incompatible behavior with the lattice site. Residual melts are progressively depleted in silica and enriched in alkali from CR4 to CR60, but silica-rich melts are observed with increasing -ΔT. In terms of Fe2+-Mg exchange, olivines obtained at -ΔT35 are always in equilibrium with the diffusive boundary layer, comprising both the interface melt next to the olivine surface and the far-field melt where all chemical gradients cease. At -ΔT85, however, the Fe2+-Mg exchange indicates two distinct equilibration stages between olivine core and far-field melt, and between olivine rim and interface melt. Partition coefficients (Kd) of Mg, Fe, Mn, Ca, and Cr calculated at the olivine-melt interface preferentially change as a function of -ΔT rather than CR. From -ΔT35 to -ΔT85, KdMg, KdFe, KdMn, and KdCr remarkably increase, whereas the opposite applies to KdCa. Through the application of equilibrium partitioning models, we found that Mg, Fe, Mn, and Ca are incorporated into the olivine lattice site at near-equilibrium proportions. This generally good agreement with modeling data demonstrates that diffusive mass transport of cations in our experiments occurred under the conditions of local equilibrium at the olivine surface. In contrast, marked deviations from the expected equilibrium are found for KCr in response to the major influence of crystal field stabilization energy on cation incorporation.

Insights into the Structural and Microscopic Origin of Magnetic Properties of the γ-Fe2O3@MnxOy Nanostructure

Hetero-nanostructures having multi-layered ferromagnetic–antiferromagnetic ultrathin films, dispersion of ferromagnetic particles to the antiferromagnetic matrix, and a core–shell model (F@AF) can exhibit an exchange bias (HEB) that will be useful for spintronic materials such as spin valves, magnetic random-access memories, and ultrahigh data storage. The spin proximity effect of F and AF in the monodispersed core–shell is not much reported. For the first time, we report the preparation of core–shell monodispersed nanoparticles of γ-Fe2O3@MnxOy having different thicknesses of shells. The microscopic origin of magnetic properties and the microscopic crystal structure are explained by experimental results such as energy-dispersive analysis of X-rays line scanning, X-ray absorption near-edge spectroscopy, and magnetic data. The values of HEB for γ-Fe2O3@MnxOy (Mn6) and γ-Fe2O3@MnxOy (Mn12) are found to be 8 and 79 Oe, respectively. Also, possible theoretical models such as crystal field stabilization energy for normal or inverse spinel structures and possible magnetic proximity interactions in core@shell models are discussed. Interestingly, samples show the heating behavior required for hyperthermia under an AC magnetic field, and materials will be potential for hyperthermia cancer therapy. Thermal decomposition of γ-Fe2O3@MnxOy produces α-Fe2–2xMn2xO3 at 550 °C, but their unit cell volumes are almost the same even after occupancy of 12 at. % Mn3+ in Fe3+ sites, and the origin of this behavior is explained for the first time.

The interaction of flotation reagents with metal ions in mineral surfaces: A perspective from coordination chemistry

The selective interaction between reagents and mineral surfaces is the core basis of mineral flotation separation. This paper creatively proposes a perspective from coordination chemistry to clarify the interaction mechanism of reagents with mineral surfaces systematically and profoundly. The metal ion in mineral surface is far different from the free ion. The former is in a semi-constrained state, causing the properties of surface metal ions to be greatly affected by surface structures and properties of surrounding atoms. Based on coordination chemistry, the π-backbonding model is advanced for the interaction between sulfhydryl collectors and sulphide minerals. It is of interest that with more π electron pairs, the surface metal ion is more likely to interact with sulfhydryl collectors containing unoccupied π orbitals; with greater polarizability, the metal ion is more prone to covalent interactions with sulfhydryl collectors. In addition, the unoccupied orbitals play a crucial role in selectivity of depressants. For example, the depressants NaCN and Ca(OH)+ containing unoccupied π orbitals can strongly depress pyrite holding π electron pairs, but can hardly depress galena possessing no π electron pair. Furthermore, the crystal field stabilization energy resulting from the interaction between reagents and surface metal ions can influence the stability of reagent adsorption, and can adequately explain the order of flotation critical pH for sulphide minerals. The coordination theory sheds new light on the interaction mechanism between flotation reagents and mineral surfaces.

K-Ion Battery Cathode Design Utilizing Trigonal Prismatic Ligand Field.

The intrinsic physical and chemical properties of materials are largely governed by the bonding and electronic structures of their fundamental building units. The majority of cathode materials contain octahedral TMO6 (TM = transition metal), which dominates the redox chemistry during electrochemical operation. As a less symmetric form of TMO6 , the trigonal prismatic geometry is not a traditionally favored coordination configuration as it tends to lose the crystal-field stabilization energy and thus generate large ligand repulsion. Herein, a K-ion battery cathode design, K2 Fe(C2 O4 )2 , is shown​, where the TMO6 trigonal prism (TP) is not only electrochemically active but stable enough to allow for excellent cycling stability. Detailed synchrotron X-ray absorption spectroscopy measurements reveal the evolution of localized fine structure, evidencing the electrochemical activity, reversibility, and stability of the TP motif. The findings are expected to expand the toolbox for the rational design of electrode materials by taking advantage of TP as a structural gene.

Mn3+ and the pink color of gem-quality euclase from northeast Brazil

Abstract Pink euclase of gem quality and centimeter size, presenting an unusual pink-orange coloration and a pink to orange pleochroism, was discovered near Livramento de Nossa Senhora, in Bahia State, Brazil. The origin of the pink coloration has been investigated using several spectroscopic techniques: UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR), luminescence, and X-ray absorption near edge structure (XANES). The coloration is mainly due to the presence of Mn3+ substituted to octahedral Al3+ that causes an intense split band at about 18 500 and 21 000 cm−1. The crystal field splitting Dq, crystal field stabilization energy (CFSE), and Racah parameter B for Mn3+ are 2055.5 cm−1, 147 kJ/mol, and 886 cm−1, respectively. The Mn3+ molar extinction coefficient varies as a function of polarization, between 23 and 55 L.mol−1·cm−1. An additional absorption band, near 24 000 cm−1, together with the rising background toward the UV, tentatively assigned to the O → Fe3+ OMCT, contributes to the pink-orange hue. The in-situ UV-Vis-NIR spectra on heating up to 500 °C show a color change toward an intense, stable pink color. CIE colorimetric parameters demonstrate that the color of the investigated euclase remains in the pink domain before and after heat treatment. In the absence of Mn2+, shown by EPR and luminescence, the presence of Mn3+ evidences oxidative formation conditions due to contamination of the hydrothermal fluids by the surrounding host rock.

Structure and magnetic behavior of sol-gel grown spinel NixMn3-xO4 nanoparticles: Effect of Ni fraction and induction of superparamagnetism at room temperature

Spinel NixMn3-xO4 nanostructures have attracted a huge research interest due to their applications in catalysis, electrocatalysis, high-performance supercapacitors, lithium-ion batteries, among others. However, those applications strongly depend on the Ni:Mn ratio, valence states and spatial distribution of cations in the spinel lattice. Using a low-temperature sol-gel process, we synthesized NixMn3-xO4 nanoparticles of 14–26 nm average sizes with different Ni contents. Effects of Ni incorporation on the morphology, structure and magnetic properties of the nanostructures were studied by SEM, XRD, XPS, Raman spectroscopy and VSM. While a high Ni content in the spinel nanostructures causes lattice shrinkage, lattice expansion at lower Ni content occurs due to higher occupancy of Mn2+ ions in tetrahedral sites. Structural and magnetic behaviors of the nanostructures were explained by considering the crystal field stabilization energies of the cations. We demonstrate that superparamagnetic behavior can be induced in the NixMn3-xO4 nanostructures by incorporating Ni at x>1.0.