Role of Dy 4felectrons on magnetic coupling and reorientation in DyFeO3.

Spin reorientation transition is an ubiquitous phenomenon observed in magnetic rare earth orthferrites RFeO3, which has garnered significant attention in recent years due to its potential applications in spintronics or magnetoelectric devices. Although a plenty of experimental works suggest that the magnetic interaction between R3+and Fe3+spins is at the heart of the spin reorientation, but a direct and conclusive theoretical support has been lacking thus far, primarily due to the challenging nature of handling R 4felectrons. In this paper, we explored DyFeO3as an example by means of comprehensive first principles calculations, and compared two different approaches, where the Dy 4felectrons were treated separately as core or valence states, aiming to elucidate the role of Dy 4felectrons, particularly in the context of the spin reorientation transition. The comparison provides a solid piece of evidence for the experimental argument that the Dy3+-Fe3+magnetic interactions play a vital role in triggering spin reorientation of Fe3+moments at low temperatures. The findings revealed here not only extend our understanding on the underlying mechanism for spin reorientation transition in RFeO3, but also highlight the importance of explicit description of R 4felectrons in rationally reproducing their structural, electronic and magnetic properties.

Pressure-induced structural and magnetic ordering transitions in the J1-J2 square lattice antiferromagnets AMoOPO4Cl (A = K, Rb).

By means of ab initio density functional theory calculations taking into account electronic correlation and van der Waals force, we conducted comprehensive studies of the electronic and magnetic properties, as well as structural and magnetic ordering evolution under pressure of the square lattice antiferromagnets AMoOPO4Cl (A = K, Rb) containing Mo5+ ions with , theoretically predicted as the potential candidates for achieving quantum phases, existing in the boundary regimes for square lattice magnets. Our results indicate that the columnar antiferromagnetic ordering, experimentally determined, is the magnetic ground state of the ambient P4/nmm phase, stabilized by the predominant antiferromagnetic next nearest neighbor interaction J2 in the diagonal directions of the square lattice, regardless of the effective Hubbard amendment values. More importantly, the P4/n phase, involving the mutual twisting of the MoO5Cl and PO4 polyhedra, satisfactorily reproduces the experimentally observed structural transition and the subsequent magnetic ordering transition from columnar antiferromagnetic ordering to Néel antiferromagnetic one, identified to be the appropriate high pressure structure. Furthermore, the mechanism underlined responsible for the magnetic ordering transition at high pressure has been disclosed in terms of density of states and spin density isosurface analysis across the transition. The loss of mirror plane symmetry in the P4/n phase activates the P 3s orbitals to participate in the magnetic interaction, giving rise to a competitive ferromagnetic superexchange interaction, in addition to antiferromagnetic direct one, and consequently initiating the magnetic ordering transition. The insights revealed here not only deepen our understanding of the electronic properties and structural and magnetic ordering transitions under high pressure of square lattice antiferromagnets AMoOPO4Cl (A = K, Rb), but also push the boundaries of knowledge by recognizing the role of nonmagnetic ions P 3s in magnetic exchange coupling.

Role of V-V dimerization on electronic and magnetic properties of ilmenite-type CoVO3.

Structural, electronic and magnetic properties of ilmenite-type CoVO3have been explored via the generalized gradient approximation + effective HubbardUeffcorrection, in the framework of density functional theory. Our results indicate that high temperature rhombohedralR3-phase is metallic with oxidation states and electronic configurations Co2+(t2g↑3eg↑2t2g↓2eg↓0), V4+(t2g↑1eg↑0t2g↓0eg↓0), respectively, while low temperature triclinicP1-phase, induced from spin-Peierls transition in the V-V dimerization manner, is insulating, maintaining charge and electronic states unchanged. Furthermore, the A-type antiferromagnetic ordering, where the ferromagnetic honeycomb layers are anti-aligned along the stacking axis, is identified to be the magnetic ground state for the low temperature phase, in nice agreement with experimental findings, analogous to CoTiO3. The unexpected intralayer ferromagnetic couplings can be attributed to the intraorbitalt2g-t2gexchange coupling, which was assumed to be small earlier and ignored, but actually large in honeycomb cobaltates with 3d7electronic configuration. In addition, the computed magnetic moment on Co2+ion ranges from 2.5 to 2.7µB, HubbardUeffdependent, close to idealS= 3/2 state, rather than the anticipatedJeff= 1/2 state. Furthermore, the supplemental calculations, taking spin-orbit coupling (SOC) into account, uncover faint orbital moments of 0.21-0.27µBat the Co site, illustrating the insignificance of SOC. Except for the inevitable trigonal distortions, the excessive structural distortion triggered by the formation V-V dimerization, i.e. the breaking of trigonal symmetry around Co2+, further lifts the degeneracy oft2gorbitals and increases crystal field splitting, driving it away from potential candidates for realizing Kitaev model physics.

Homocoupling of benzyl pyridyl ethers via visible light-mediated deoxygenation.

The photocatalytic coupling of ethers is uncommon because of the challenges in breaking C-O bonds and low selectivity. Herein, we report a visible light-mediated deoxygenation homocoupling of benzyl pyridyl ethers via their pyridium salts. This approach enables C(sp3)-O bond homolysis under mild conditions. Mechanistic experiments support the radical nature of the reaction. This method is highly compatible with electron-withdrawing groups and has potential applications for drug precursor synthesis.

High-nuclearity and thiol protected core-shell [Cu75(S-Adm)32]2+: distorted octahedra fixed to Cu15 core via strong cuprophilic interactions.

Atomically precise nanoclusters have a critical role in understanding the structure-property relationships at the atomic level. Copper nanoclusters have attracted considerable attention, but the synthesis is limited because of susceptibility to oxidation. Herein, we developed a reduction speed controlling method to synthesize [Cu75(S-Adm)32]2+ (HS-Adm: 1-Adamantanethiol) nanocluster and reveal the key steps in the nucleation process. Cu75 was first observed and characterized with the following features: (i) composed of a face-centered cubic Cu15 kernel and a Cu60 caged shell including 12 distorted octahedra. (ii) The observation of the shortest Cu-Cu bond (2.166(7) Å) in the Cu nanoclusters, which could result from the distortion of the octahedron. (iii) The sole µ3-S mode of S, which plays two roles as a vertex and bridge atom to connect Cu atoms. This work presents a unique nanoball Cu nanocluster with strong cuprophilic interaction and provides a novel method to expand the family of Cu nanoclusters as well.

Synthesis of Unnatural α-Amino Acids from (Pyridin-2-yl) Carbamate via CIPE-Induced Carbonyl Migration.

Synthetic methods of unnatural α-amino acids have always been the focus of extensive research due to their significant bioactivities. However, convenient transition-metal-free catalyzed methods are still in demand. Herein, we report a novel strategy for the construction of an unnatural α-amino acid skeleton via intramolecular rearrangement of carbamates, which are readily available from amines and their common protecting groups. This rearrangement could afford a variety of amino ester products in up to 98% yield, even in gram-scale reaction. The reaction mechanism was studied in detail through experiments and theoretical calculations. The complex-induced proximity effect (CIPE) from the 2-pyridyl group is shown to be indispensable for this transformation.

Electronic and Magnetic Properties of Spin-Orbit-Entangled Honeycomb Lattice Iridates MIrO3 (M = Cd, Zn, and Mg).

By means of density functional theory calculations with the inclusion of spin-orbit coupling, we present a comprehensive investigation of the structural, electronic, and magnetic properties of the novel series of ilmenite-type honeycomb lattice iridates MIrO3 (M = Cd, Zn, and Mg), the potential candidates for realizing the quantum spin liquid. Our findings are as follows: (i) the structural relaxations could not properly capture the abnormal thin two-dimensional honeycomb IrO6 layers in CdIrO3, making the experimentally proposed crystal structure questionable. Furthermore, the calculations within the experimental structure could not correctly determine the magnetic ground state; however, the results within the optimized one rectify this scenario and provide a precise and reasonable description of its electronic and magnetic properties, which is in good agreement with the experimental observations and that of Zn and Mg analogues. In this regard, we hope that our report will inspire additional studies on this issue and eventually resolve the crystal structure of CdIrO3. (ii) We identified that the magnetic ground state of this series of iridates MIrO3 is the zigzag antiferromagnetic ordering, where ferromagnetic zigzag chains are coupling antiferromagnetically across the bridging bonds within a hexagon. (iii) Though it is widely assumed that all the iridates can be well described based on the spin-orbit-assisted Jeff = 1/2 Mott insulating state model, detailed analysis of electronic band structures indicates that the formation of quasimolecular orbitals (QMOs) within a hexagon plays a non-negligible role in appropriately depicting the electronic and magnetic properties. Finally, (iv) we found that all the antiferromagnetic patterns are insulating with finite band gaps. Clarifying the effect of magnetic ordering on the electronic structures is important because it reminds us of potential erroneous identification/prediction of the ground state. The results suggest that precisely determining the magnetic ground state and adopting it in the simulations are imperative for faithfully rendering the electronic properties of a compound. Our results underline the importance of structural factor, spin-orbit coupling, correlation correction, the formation of the QMOs within the hexagon, as well as magnetic ordering in elucidating the electronic structure of a series of ilmenite-type honeycomb lattice iridates MIrO3.

Finding Key Factors for Efficient Water and Methanol Activation at Metals, Oxides, MXenes, and Metal/Oxide Interfaces.

Activating water and methanol is crucial in numerous catalytic, electrocatalytic, and photocatalytic reactions. Despite extensive research, the optimal active sites for water/methanol activation are yet to be unequivocally elucidated. Here, we combine transition-state searches and electronic charge analyses on various structurally different materials to identify two features of favorable O-H bond cleavage in H2O, CH3OH, and hydroxyl: (1) low barriers appear when the charge of H moieties remains approximately constant during the dissociation process, as observed on metal oxides, MXenes, and metal/oxide interfaces. Such favorable kinetics is closely related to adsorbate/substrate hydrogen bonding and is enhanced by nearly linear O-H-O angles and short O-H distances. (2) Fast dissociation is observed when the rotation of O-H bonds is facile, which is favored by weak adsorbate binding and effective orbital overlap. Interestingly, we find that the two features are energetically proportional. Finally, we find conspicuous differences between H2O/CH3OH and OH activation, which hints toward the use of carefully engineered interfaces.

Synthesis of gem-Dimethylcyclopentane-Fused Arenes with Various Topologies via TBD-Mediated Dehydro-Diels-Alder Reaction.

The development of efficient methods for the synthesis of substituted polycyclic arenes with various topologies is in high demand due to their excellent electrical and optical properties. In this work, a series of gem-dimethylcyclopentane-fused arenes with more than ten topologies were synthesized via a 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD)-mediated dehydro-Diels-Alder reaction with moderate to good yields. The introduction of the near-planar gem-dimethylcyclopentane moiety not only impacts the molecular conjugative system but also regulates the intermolecular π-π interactions and crystal packing, which are critical for the photoelectric performance of arenes. The photophysical properties, molecular geometry, molecular packing of these compounds, and electrochemical properties were investigated by UV-vis absorption, fluorescence emission spectra, DFT calculations, single-crystal X-ray structure analysis, and cyclic voltammetry study.

[AuAg26(SR)18S]- Nanocluster: Open Shell Structure and High Faradaic Efficiency in Electrochemical Reduction of CO2 to CO.

For atomically precise metal nanoclusters, distinctive molecular architectures and promising applications are urgently required to be intensively explored. Herein, we have first reported the open shell structure of the [AuAg26(S-Adm)18S]- nanocluster and its application in the electrochemical reduction of CO2. The X-ray crystal structure of the AuAg26 nanocluster is composed of a AuAg12 icosahedron kernel and a Ag14(SR)18S open shell. The shell includes a Ag6(SR)3S, a Ag5(SR)6, and three Ag(SR)3 motifs. It is the first time twisty propeller-like Ag5(SR)6 and trefoil-like Ag6(SR)3S motifs in metal nanoclusters have been observed. Due to the novel open shell configuration of Ag14(SR)18S, four triangular facets of the kernel are exposed. The AuAg26 nanocluster shows excellent catalytic activity in the electrochemical reduction of CO2 to CO. The Faradaic efficiency of CO is up to 98.4% under -0.97 V. The electrochemical in situ infrared study and DFT calculations demonstrate that the open shell structure of the AuAg26 nanocluster is beneficial to the forming of intermediate COOH* in the electrochemical reduction of CO2 to CO.

Magnetic Interactions in ZnMnO3: Active Role of Zn 3d10 Orbitals, in Comparison with MgMnO3.

The ilmenite-type MgMnO3 and ZnMnO3 with honeycomb Mn layers exhibit distinctive magnetic ground states. In experiments, MgMnO3 exhibits a Néel antiferromagnetic alignment, in which both nearest-neighbor (NN) J1 and next-nearest-neighbor (NNN) J2 exchange interactions are antiferromagnetic, while ZnMnO3 has zigzag antiferromagnetic ordering with NN ferromagnetic and NNN antiferromagnetic coupling. On the basis of ab initio band structure calculations, we explain the deviation of NN J1 exchange coupling from antiferromagnetic (MgMnO3) to ferromagnetic (ZnMnO3) as originating from the intensive hybridization between the occupied Zn 3d10 orbitals with those of the bridging O 2p states, strongly depending on the position of the orbitals. In addition, our results indicate that, in combination with the NN J1 coupling, the considerably large third-nearest-neighbor (TNN) J3 exchange interaction plays an important role in erecting the magnetic ground states, rather than the experimentally proposed NNN J2. Furthermore, our findings highlight the important role of not only the electronic configurations but also the positions of the nonmagnetic cations in determining the essence of the magnetic exchange interactions. Therefore, the hybridization effect of nonmagnetic cations should not be dismissed in an analysis of the magnetic properties of transition-metal oxides.

Boosting the catalysis of gold by O2 activation at Au-SiO2 interface.

Supported gold (Au) nanocatalysts have attracted extensive interests in the past decades because of their unique catalytic properties for a number of key chemical reactions, especially in (selective) oxidations. The activation of O2 on Au nanocatalysts is crucial and remains a challenge because only small Au nanoparticles (NPs) can effectively activate O2. This severely limits their practical application because Au NPs inevitably sinter into larger ones during reaction due to their low Taman temperature. Here we construct a Au-SiO2 interface by depositing thin SiO2 layer onto Au/TiO2 and calcination at high temperatures and demonstrate that the interface can be not only highly sintering resistant but also extremely active for O2 activation. This work provides insights into the catalysis of Au nanocatalysts and paves a way for the design and development of highly active supported Au catalysts with excellent thermal stability.

Trends in C-O and N-O bond scission on rutile oxides described using oxygen vacancy formation energies.

Reactivity trends on transition metals can generally be understood through the d-band model, but no analogous theory exists for transition metal oxides. This limits the generality of analyses in oxide-based catalysis and surface chemistry and has motivated the appearance of numerous descriptors. Here we show that oxygen vacancy formation energy (ΔE Vac) is an inexpensive yet accurate and general descriptor for trends in transition-state energies, which are usually difficult to assess. For rutile-type oxides (MO2 with M = 3d metals from Ti to Ni), we show that ΔE Vac captures the trends in C-O and N-O bond scission of CO2, CH3OH, N2O, and NH2OH at oxygen vacancies. The proportionality between ΔE Vac and transition-state energies is rationalized by analyzing the oxygen-metal bonds, which change from ionic to covalent from TiO2 to NiO2. ΔE Vac may be used to design oxide catalysts, in particular those where lattice oxygen and/or oxygen vacancies participate in the catalytic cycles.

Structure of the Au23-x Agx (S-Adm)15 Nanocluster and Its Application for Photocatalytic Degradation of Organic Pollutants.

Ligands play an important role in determining the atomic arrangement within the metal nanoclusters. Here, we report a new nanocluster [Au23-x Agx (S-Adm)15 ] protected by bulky adamantanethiol ligands which was obtained through a one-pot synthesis. The total structure of [Au23-x Agx (S-Adm)15 ] comprises an Au13-x Agx icosahedral core, three Au3 (SR)4 units, and one AgS3 staple motif in contrast to the 15-atom bipyramidal core previously seen in [Au23-x Agx (SR)16 ]. UV/Vis spectroscopy indicates that the HOMO-LUMO gap of [Au23-x Agx (S-Adm)15 ] is 1.5 eV. DFT calculations reveal that [Au19 Ag4 (S-Adm)15 ] is the most stable structure among all structural possibilities. Benefitting from Ag doping, [Au23-x Agx (S-Adm)15 ] exhibits drastically improved photocatalytic activity for the degradation of rhodamine B (RhB) and phenol under visible-light irradiation compared to Au23 nanoclusters.

Self-activated surface dynamics in gold catalysts under reaction environments.

Nanoporous gold (NPG) with sponge-like structures has been studied by atomic-scale and microsecond-resolution environmental transmission electron microscopy (ETEM) combined with ab initio energy calculations. Peculiar surface dynamics were found in the reaction environment for the oxidation of CO at room temperature, involving residual silver in the NPG leaves as well as gold and oxygen atoms, especially on {110} facets. The NPG is thus classified as a novel self-activating catalyst. The essential structure unit for catalytic activity was identified as Au-AgO surface clusters, implying that the NPG is regarded as a nano-structured silver oxide catalyst supported on the matrix of NPG, or an inverse catalyst of a supported gold nanoparticulate (AuNP) catalyst. Hence, the catalytically active structure in the gold catalysts (supported AuNP and NPG catalysts) can now be experimentally unified in low-temperature CO oxidation, a step forward towards elucidating the fascinating catalysis mechanism of gold.

Spatially Confined Assembly of Monodisperse Ruthenium Nanoclusters in a Hierarchically Ordered Carbon Electrode for Efficient Hydrogen Evolution.

The redox units of polyaniline (PAni) are used cooperatively, and in situ, to assemble ruthenium (Ru) nanoclusters in a hierarchically ordered carbon electrode. The oxidized quinonoid imine (QI) units in PAni bond Ru complex ions selectively, whereas reduced benzenoid amine (BA) units cannot. By electrochemically tuning the ratio of QI to BA, Ru complexes are spatially confined in the outer layer of hierarchical PAni frameworks. Carbonization of Ru-PAni hybrids induces nucleation on the outer surface of the carbon support, generating nearly monodisperse Ru nanoclusters. The optimized catalyst has a low loading of approximately 2 wt % Ru, but exhibits a mass activity for the hydrogen evolution reaction that is about 6.8 times better than commercial 20 wt % Pt/C catalyst.

Light-enhanced acid catalysis over a metal-organic framework.

A Brønsted acid-functionalized metal-organic framework (MOF), MIL-101-SO3H, was prepared for acid-engaged esterification reactions. Strikingly, for the first time, the MOF exhibits significantly light-enhanced activity and possesses excellent activity and recyclability, with even higher activity than H2SO4 under light irradiation.

Charge ordering and magnetic frustration in CsFe2F6.

The structural, electronic and magnetic properties of a charge-ordered iron fluoride material CsFe2+Fe3+F6 have been explored by density functional theory calculations based on the generalized gradient approximation + U approach, which was implemented in the VASP code. The material exhibits a 3D pyrochlore-related structure which consists of corner-shared Fe2+F6 and Fe3+F6 octahedra. Our results confirm that CsFe2F6 is a Mott-Hubbard insulator, and bears a magnetically frustrated ground state in which the localized 3d electrons are antiferromagnetically coupled between the homogeneous Fe ions (Fe3+-Fe3+ along the b axis, and Fe2+-Fe2+ along the a axis), while interactions between the heterogeneous Fe ions (Fe3+-Fe2+ along the c axis) are frustrated, consistent with Goodenough-Kanamori superexchange interactions. Although the disproportionation of the total 3d charge is extremely low, explicit evidence is provided on the charge ordering by an order parameter, which is defined as the difference in minority d yz orbital (in the local coordinates) occupations between the Fe3+ and Fe2+ cations. In addition, spin ordering and the spin-orbit coupling effect play an insignificant role in the charge ordering and the preferential occupation of the d yz orbital scenario in CsFe2F6.

Establishing and Understanding Adsorption-Energy Scaling Relations with Negative Slopes.

Adsorption-energy scaling relations are widely used for the design of catalytic materials. To date, only linear scaling relations are known in which the slopes are positive. Considering the adsorption energies of F, O, N, C, and B on transition metals, we show here that scaling relations with negative slopes also exist between certain adsorbates. The origin of such unconventional scaling relations is analyzed in terms of common descriptors such as d-band center, work function, number of outer electrons, electronic charge on the adsorbates, integrated crystal orbital overlap populations, and crystal orbital Hamilton populations. Conventional scaling relations are formed between adsorbates such as F, O, N, and C, which create ionic-like bonds with surfaces. Conversely, anomalous scaling relations are established between those and covalently bound adsorbates such as B. This widens the theory of adsorption-energy scaling relations and opens new avenues in physical chemistry and catalysis, for instance, in direct borohydride fuel cells.

Stepwise displacement of catalytically active gold nanoparticles on cerium oxide.

Aberration-corrected environmental transmission electron microscopy (ETEM) proved that catalytically active gold nanoparticles (AuNPs) move reversibly and stepwise by approximately 0.09 nm on a cerium oxide (CeO2) support surface at room temperature and in a reaction environment. The lateral displacements and rotations occur back and forth between equivalent sites, indicating that AuNPs are loosely bound to oxygen-terminated CeO2 and may migrate on the surface with low activation energy. The AuNPs are likely anchored to oxygen-deficient sites. Observations indicate that the most probable activation sites in gold nanoparticulate catalysts, which are the perimeter interfaces between an AuNP and a support, are not structurally rigid.