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The atomic structures, electronic structures, magnetic properties, and spin states of BiCoO3 multiferroic material under hydrostatic pressure are comprehensively investigated by using first‐principles calculation based on density functional theory. Firstly, we found the pressure‐tuned structural symmetry transition from tetragonal P4 mm (No. 99) to cubic Pm3¯$\bar{3}$m (No. 221) space group. The structural transformation prompts the Co─O polyhedral coordination transfer from a CoO5 pyramidal to a CoO6 distorted octahedron. Secondly, the pressure‐induced magnetic change from C‐type antiferromagnetic state to ferromagnetic state and then to paramagnetic configuration occurred after continuous compression of the volume. Essentially, the fundamental reason for the transition of the magnetic structure lies in the change of the internal atomic structure, such as the pressure induced abrupt changes of Co─O bond length and bond angle. Meanwhile, an obvious volume collapse was observed when the pressure was applied to 51–56 GPa. Finally, as the pressure increases, the magnetism changes from C‐type antiferromagnetic state to paramagnetic configuration, accompanying the transformation from high spin state with b2g2eg2a1g1b1g1 configuration in pyramid structure to low spin state with t2g6eg0 in octahedral field. Therefore, our results demonstrate that applied hydrostatic pressure in BiCoO3 can trigger the transformation of structure, magnetism, charge, and spin state. [ABSTRACT FROM AUTHOR]

High‐voltage LiCoO2 (LCO) attracts great interest due to its high theoretical capacity, however, the aggravated oxygen redox, Co dissolution, and lattice degradation at high voltage potentially induce the instability of crystal structural and cathode–electrolyte interphase, and can ultimately lead to severe capacity fading. Herein, a design strategy of spin modulation is presented to stabilize the surface and bulk structure of the commercial LiCoO2 (C‐LCO). The prepared high‐spin state LiCoO2 via crystal field modulation elevates the Co─O band gap, suppresses the electronic compensation of oxygen at high voltage, and reduces the side reactions of reactive oxygen and dissolved Co ions with the electrolyte, which greatly restrains the irreversible phase transition from O3 to H1‐3 and the degeneration of cathode–electrolyte interphase. As a result, the spin‐modulated LiCoO2 shows significantly improved electrochemical performances including high discharge capacity, stable cycling behavior, and enhanced rate capability. This work based on spin modification by crystal field modulation can apply to other layered transition metal oxide cathodes, providing a new avenue for developing high‐energy–density cathodes. [ABSTRACT FROM AUTHOR]

Integrating controllable spin states into single‐molecule magnets (SMMs) enables precise manipulation of magnetic interactions at a molecular level, but remains a synthetic challenge. Herein, we developed a 3d–4f metallacrown (MC) magnet [DyNi5(quinha)5(Clsal)2(py)8](ClO4) ⋅ 4H2O (H2quinha=quinaldichydroxamic acid, HClsal=5‐chlorosalicylaldehyde) wherein a square planar NiII is stabilized by chemical stacking. Thioacetal modification was employed via post‐synthetic ligand substitutions and yielded [DyNi5(quinha)5(Clsaldt)2(py)8](ClO4) ⋅ 3H2O (HClsaldt=4‐chloro‐2‐(1,3‐dithiolan‐2‐yl)phenol). Thanks to the additional ligations of thioacetal onto the NiII site, coordination‐induced spin state switching (CISSS) took place with spin state altering from low‐spin S=0 to high‐spin S=1. The synergy of CISSS effect and magnetic interactions results in distinct energy splitting and magnetic dynamics. Magnetic studies indicate prominent enhancement of reversal barrier from 57 cm−1 to 423 cm−1, along with hysteresis opening and an over 200‐fold increment in coercive field at 2 K. Ab initio calculations provide deeper insights into the exchange models and rationalize the relaxation/tunnelling pathways. These results demonstrate here provide a fire‐new perspective in modulating the magnetization relaxation via the incorporation of controllable spin states and magnetic interactions facilitated by the CISSS approach. [ABSTRACT FROM AUTHOR]

A new iron(III) complex (Et3NH)2[Fe(L)2](ClO4)·MeOH (1) where H2L = 2-{(E)-[2-hydroxyphenyl)imino]methyl}phenol has been synthesised and characterised by single crystal XRD, elemental analysis and DC magnetic susceptibility measurements. The dianionic ligands L2− coordinate in a tridentate fashion with the Fe(III) through their deprotonated phenolic oxygens and azomethine nitrogen atoms, resulting in a trans-FeO4N2 chromophore. Variable-temperature magnetic measurements were performed between 300 and 5 K under an applied field of 0.1 T and show that 1 is in the high spin state (S = 5/2) over the whole measured temperature range. This is confirmed by Mössbauer spectroscopy at 77 and 300 K. [ABSTRACT FROM AUTHOR]

The spin states of active sites have a significant impact on the adsorption/desorption ability of the reaction intermediates during the oxygen evolution reaction (OER). Sulfide spinel is not generally considered a highly efficient OER catalyst owing to the low spin state of Co3+ and the lack of unpaired electrons available for adsorption of reaction intermediates. Herein, it is proposed a novel Nd‐evoked valence electronic adjustment strategy to engineer the spin state of Co ions. The unique f‐p‐d orbital electronic coupling effect stimulates the rearrangement of Co d orbital electrons and increases the eg electron filling to achieve high‐spin state Co ions, which promotes charge transport by propagating a spin channel and generates a high number of active sites for intermediate adsorption. The optimized CuCo1.75Nd0.25S4 catalyst exhibits outstanding electrocatalytic properties with a low overpotential of 320 mV at 500 mA cm−2 and a 48 h stability at 300 mA cm−2. In situ synchrotron radiation infrared spectra confirm the quick accumulation of key *OOH and *O intermediates. This work deepens the comprehensive understanding of the relationship between OER activity and spin configurations of Co ions and offers a new design strategy for spinel compound catalysts. [ABSTRACT FROM AUTHOR]

LaCoO3 is well-known for its unique thermally induced transition of Co3+ (3d6) ions from a low spin (LS) state to a higher spin state of intermediate spin (IS) state or high spin (HS) state, due to a delicate balance between crystal-field splitting and Hund’s coupling. In this work, we try to stabilize all possible spin states in the same initial structural model and further investigate the spin-state effect on the redox performance of LaCoO3. We find that an initial model of pseudocubic with R3¯c tilting octahedra was effective in stabilizing all possible spin states. The oxygen vacancy formation values of LS > HS + LS > HS > IS indicate that the IS state is the most optimal spin state in oxygen vacancy formation, which results from a weakened Co-O bonding energy by eg orbital occupation. The oxygen migration barriers of LS > IS > HS + LS > HS show that oxygen migration is easier in the relatively loose structure and thus LS structure is the most unfavorable in oxygen migration. Combining the oxygen vacancy formation and migration results, we conclude that the higher spin states of IS and HS are more beneficial than LS in oxygen conduction. Our results confirm the influence of the spin-state effect on oxygen conduction and show that spin-state regulation is a good strategy for improving the redox performance of perovskites.

Iron is an impurity widely occurred in sphalerite, and its effect on sphalerite flotation is complex. In this work, the effects of iron content and spin state on electronic properties and floatability of iron-bearing sphalerite are comprehensively studied using density functional theory Hubbard U (DFT+U) calculations combined with coordination chemistry flotation. The band gap of ideal sphalerite is 3.723 eV, and thus electron transition is difficult to occur, resulting in poor floatability. The results suggest the band gap of sphalerite decreases with increasing iron content. For low iron content, the decreased band gap facilitates electron transition; at this case, Fe2+ in a high-spin state possesses one π electron pair, which can form a weak π-backbonding with xanthate, causing increasing floatability. However, for medium and high iron-bearing sphalerite, with the further decrease of band gap, Fe2+ is oxidized to Fe3+ due to electrochemical interaction, and hence π-backbonding is eliminated, leading to lower floatability of iron-bearing sphalerite, which is consistent with the flotation experimental results. This work could give a deeper understanding of how sphalerite flotation behaviors are affected by iron content.

The processing and analysis of synchrotron data can be a complex task, requiring specialized expertise and knowledge. Our previous work addressed the challenge of X-ray emission spectrum (XES) data processing by developing a standalone application using unsupervised machine learning. However, the task of analyzing the processed spectra remains another challenge. Although the non-resonant Kβ XES of 3d transition metals are known to provide electronic structure information such as oxidation and spin state, finding appropriate parameters to match experimental data is a time-consuming and labor-intensive process. Here, a new XES data analysis method based on the genetic algorithm is demonstrated, applying it to Mn, Co and Ni oxides. This approach is also implemented as a standalone application, Argonne X-ray Emission Analysis 2 (AXEAP2), which finds a set of parameters that result in a high-quality fit of the experimental spectrum with minimal intervention. AXEAP2 is able to find a set of parameters that reproduce the experimental spectrum, and provide insights into the 3d electron spin state, 3d–3p electron exchange force and Kβ emission core-hole lifetime.

A new iron(III) complex (Et3NH)2[Fe(L)2](ClO4)·MeOH (1) where H2L = 2-{(E)-[2-hydroxyphenyl)imino]methyl}phenol has been synthesised and characterised by single crystal XRD, elemental analysis and DC magnetic susceptibility measurements. The dianionic ligands L2− coordinate in a tridentate fashion with the Fe(III) through their deprotonated phenolic oxygens and azomethine nitrogen atoms, resulting in a trans-FeO4N2 chromophore. Variable-temperature magnetic measurements were performed between 300 and 5 K under an applied field of 0.1 T and show that 1 is in the high spin state (S = 5/2) over the whole measured temperature range. This is confirmed by Mössbauer spectroscopy at 77 and 300 K.

The electronic state in terms of charge and spin of metal sites is fundamental to govern the catalytic activity of a photocatalyst. Herein, we show that modulation of the electronic states of Cu sites, without changing the coordination environments, of two metal‐organic supramolecular assemblies based on π⋅⋅⋅π stacking can significantly improve photocatalytic activity. The use of these heterogeneous photocatalysts, without using noble metal cocatalysts, resulted in an increase of the hydrogen production rate from 522 to 3620 μmol h−1 g−1. A systematical analysis revealed that the charge density and spin density of the metal centers are efficiently modulated via the modulation of the coordination fields around active copper (II) centers by the variation of the non‐coordination groups of terminal ligands, leading to the significant enhancement of photocatalytic activity. This work provides an insight into the electronic state of active metal centers for designing high‐performance photocatalysts. [ABSTRACT FROM AUTHOR]