Electronic Configuration Research Articles

Orbital and Electrical Dual Function of Polymer Intercalant for Promoting NH4+ Storage in Vanadium Oxide Anode

AbstractPolymer‐intercalated metal oxides have attracted considerable attention for ammonium ions (NH4+) storage due to their enhanced interlayer space, which, through the pillar effect, facilitates rapid and efficient transport of NH4+. However, the understanding remains limited regarding how polymer intercalants affect the intrinsic structure of host materials, especially the variations in atomic orbital and electronic structural induced by the intercalants. Herein, a polyaniline‐intercalated vanadium oxide (P‐VOx) is developed and, for the first time, its NH4+ storage behavior is validated as an anode material. Using various spectroscopy techniques combined with theoretical simulation, the changes are analyzed in atomic orbital and electronic structure induced by the intercalant. Spectroscopy studies reveal that the insertion of polyaniline optimizes the electronic structure of V2O5, promoting the transition of electrons to the V 3dxy state and increasing the occupation of the V t2g orbital, thereby enhancing electrical conductivity. Computational results confirm that P‐VOx lowers the NH4+ migration barrier, thereby enhancing electron/NH4+ transfer. As a result, the P‐VOx electrode demonstrates outstanding capacity and unprecedented long‐term cycling stability. This study provides new insights into the atomic and electronic structural changes induced by the polymer intercalant and underscores the advantages of polymer‐intercalated VOx as a high‐performance electrode for NH4+ storage.

Modulating Electronic Density of Single-Atom Ni Center by Heteroatoms for Efficient CO2 Electroreduction.

Single-atom catalysts (SACs) with unique geometric and electronic configurations have triggered great interest in many important reactions. However, controllably modulating the electronic structure of metal centers to enhance catalytic performance remains a challenge. Here, the electronic structure of Ni centers over Ni1-NC SACs by introducing electron-rich phosphorus or electron-deficient boron for electrochemical CO2 reduction (CO2RR) is systematically tailored. It is found that the Ni1-PNC with Ni1-N3P site exhibits superior performance with a current density of 14.6mA cm-2 and a Faradaic efficiency of 90.6% at -0.8V versus RHE for CO production, far exceeding Ni1-NC and Ni1-BNC SACs. Detailed characterizations and theoretical calculations reveal a linear relationship between the valence state of Ni species and the CO2RR performance. The incorporation of P species facilitates the electronic localization around the Ni1 center, significantly promoting the adsorption of CO2 and the formation of key *COOH intermediate to enhance CO2RR. This work provides a feasible approach to quantitatively manipulate the electronic structure of single-atom metal sites and to rationally design highly efficient catalysts for boosted performance.

NO Oxidation States in Nonheme Iron Nitrosyls: A DMRG-CASSCF Study of {FeNO}6-10 Complexes.

Building upon an earlier study of heme-nitrosyl complexes (Inorg. Chem. 2023, 62, 20496-20505), we examined a wide range of nonheme {FeNO}6-10 complexes (the superscript represents the Enemark-Feltham count) and two dinitrosyl iron complexes using DMRG-CASSCF calculations. Analysis of the wave functions in terms of resonance forms with different [π*(NO)]i occupancies (where i = 0-4 for mononitrosyl complexes) identified the dominant electronic configurations of {FeNO}6 and {FeNO}7 complexes as FeIII-NO0 and FeII-NO0, respectively, mirroring our previous findings on heme-nitrosyl complexes. A trigonal-bipyramidal S = 1 {FeNO}8 complex with an equatorial triscarbene ligand set appears best described as a resonance hybrid of FeI-NO0 and FeII-NO-. Reduction to the corresponding S = 1/2 {FeNO}9 state was found to involve both the metal and the NO, leading to an essentially FeI-NO- complex. Further reduction to the {FeNO}10 state was found to be primarily metal-centered, leading to a predominantly Fe0-NO- configuration. Based on the weights wi of the [π*(NO)]i resonance forms, an overall DMRG-CASSCF-based π*(NO) occupation number could be derived, which was found to exhibit a linear correlation with both the NO bond distance and NO stretching frequency, allowing a readout of the NO oxidation state from the NO bond distance.

Exploring the equilibrium and non-equilibrium properties of a cooperative trinuclear spin-crossover chain: The role of elastic frustration.

Among the large family of spin-crossover (SCO) solids, recent investigations focused on polynuclear SCO materials, whose specific molecular configurations allow the presence of multi-step transitions and elastic frustration. In this contribution, we develop the first elastic modeling of thermal and dynamical properties of trinuclear SCO solids. For that, we study a finite SCO open chain constituted of successive elastically coupled trinuclear (A=B=C) blocks, in which each site (A, B, and C) may occupy two electronic configurations, namely, low-spin (LS) and high-spin (HS) states, accompanied with structural changes. Intra- and inter-molecular springs couple the sites inside and between trimers. The model also includes the change of length inside and between the trinuclear units subsequent to the spin states changes. First, we studied the mechanical relaxation of a LS chain initially prepared with HS distances, from which we dissected the dynamics of the atomic displacements for various strengths of intra- and inter-molecular elastic constants. Second, we investigated the thermal properties of the chain at equilibrium, which revealed the existence of a rich variety of behaviors, going from: gradual LS to HS transition to multiple spin transitions with the presence of self-organized spin state structures in the plateaus. The latter were identified as emerging from antagonist short- and long-range elastic interactions between intra- and inter-block size changes. The present model opens several possible extensions, among which are the cases of coupled non-linear trimer molecules as well as that of inter-chain interactions with block-block interactions, leading to unexpected hysteretic spin transitions.

Selected configuration interaction for high accuracy and compact wave functions: Propane as a case study.

Traditionally, because of the limit of full configuration interaction, complete active space (CAS) theory is most often used to model bond dissociation and other dynamical processes where the multi-reference character becomes important. Inconveniently, the CAS method is highly dependent on the choice of active space and, therefore, inherently non-black-box, in addition to the exponential scaling with respect to electrons and orbitals. This illustrates the need for methods that can accurately treat multi-reference electronic structure problems without significant dependence on input parameters. Selected configuration interaction (SCI) methods have experienced a revival in recent years because of their independence of these predicaments. SCI methods aim to exploit the sparsity of the full configuration interaction space to identify all relevant electronic configurations and, therefore, keep the wave function as compact as possible while still representing the total multi-reference electronic structure accurately. In this work, we take the recent achievement by Gao et al. to run full configuration interaction on the propane molecule in a minimal basis set (23 electrons in 26 orbitals) as an occasion to demonstrate that our SCI methods implemented in the GeneralSCI program package can achieve high energetic accuracy in conjunction with very compact wave functions, which considerably alleviate computational cost. Furthermore, we show the good performance of our SCI methods in reproducing a propane bond dissociation surface and energy. This illustrates that SCI methods can be readily applied to problems in chemical reactivity.

Manipulating d‐band Center by Interface‐Induced Dislocation in Pt@PtCu Nanowires Boosting Oxygen Reduction

AbstractEngineering the electronic configuration and intermediates adsorption behaviors of Platinum‐based catalysts is crucial for improving oxygen reduction reaction (ORR) kinetics at the cathode in proton exchange membrane fuel cells (PEMFCs), yet it remains an enormous challenge. Herein, an interface‐induced dislocation tactic through Pt/PtCu heterogeneous formation in Pt@PtCu nanowires composites (Pt@PtCu NWs) for efficient ORR is reported. Theoretical studies have proven that dislocation driven by a hybrid interface could alter electron redistribution and downshift the d‐band of Pt, thus facilitating the desorption of oxygen‐containing species and achieving outstanding ORR performance. Specifically, the as‐prepared Pt@PtCu NWs deliver exceptional ORR properties with a half‐wave of 0.940 V. Moreover, the mass activity (MA) of Pt@PtCu NWs reaches 1.17 A mgPt−1 at 0.9 V, which is 4.18 and 10.64 times higher than that of Pt NWs (0.27 A mgPt−1) and commercial Pt/C (0.11 A mgPt−1). Most importantly, Pt@PtCu NWs also prove remarkable structural stability with only a 14.5% decrease in MA compared to a 58.9% decrease for Pt/C after the durability test. Overall, this strategy of d‐band center tuning induced by hybrid‐interface‐driven dislocation provides a promising avenue for designing high‐efficiency electrocatalysts.

Selective Ions Exchange Reactions Endow Defective Heterovalent Copper‐Based Selenides With Enhanced Dielectric Polarization Response

AbstractDefective heterovalent selenides provide a spacious arena for creating emergent electromagnetic (EM) phenomena that are unattainable in the conventional constituent counterparts. However, there are still synthetic methodological challenges, and in‐depth understanding of the EM properties, particularly correlation between tailored polarization sites and dielectric polarization response, are significantly inadequate. Herein, a selective ions exchange strategy driven by concentration‐regulated (Case 1) and time‐evoked (Case 2) approaches, is innovatively proposed to design series of defective heterovalent copper‐based selenides. The controllable phase evolution tailored by concentration‐regulated mixed cation/anion exchange is responsible for heterointerfaces levels (Case 1), while Cu+/Cu2+ electronic configurations controlled by time‐evoked cation exchange accounted for further manipulating heterointerfaces/defects levels and enriching polarization sites (Case 2). The coupling of nonstoichiometric Cu2−xSe‐containing heterointerfaces, unsaturated Se vacancies and multi‐valence configurations, rather than themselves alone even at a higher level, imparted abundant polarization sites to trigger boosted polarization response for defective heterovalent selenides. Consequently, this designed defective heterovalent selenide (ZnSe/CuSe/Cu2‐xSe) deliveres a broad bandwidth of 6.89 GHz compare to parent ZnSe without dielectric response, outperforming most reported metal selenides until now. This innovative strategy overcame the bottlenecks of conventional synthetic methodology, providing a paradigm for fabricating sophisticated defective heterovalent materials for versatile applications beyond EM absorption.

N-Doped Zigzag-Type Aromatic Truncated Cone Belts.

Zigzag aromatic hydrocarbon belts, ultrashort segments of zigzag carbon nanotubes, have been fascinating in the chemistry community for more than a half century because of their aesthetically appealing molecular nanostructures and tantalizing applications. Precise introduction of heteroatoms of distinct electronegativity and electronic configuration can create various heterocyclic aromatic nanobelts with novel physical and chemical properties. Here, we report the synthesis of unprecedented N-doped zigzag-type aromatic belts, belt[n]pyrrole[n]pyridines (n = 6-8), from multiple intramolecular Caryl-Caryl homocoupling reactions of readily available azacalix[n](3,5-dibromopyridine)s. These compounds adopt globally π-conjugated belt structures and display unique photophysical and electrochemical properties. The truncated cone cavity of belt[8]pyrrole[8]pyridine was used as the outstanding host to form very stable 2:1 encapsulation complexes with fullerenes. This work opens a new avenue to the rational design and efficient synthesis of aromatic belts of distinct topological structures and tailor-made properties, which are invaluable in applications in materials and supramolecular chemistry.

Unraveling 3d Transition Metal (Ni, Co, Mn, Fe, Cr, V) Ions Migration in Layered Oxide Cathodes: A Pathway to Superior Li-Ion and Na-Ion Battery Cathodes.

Li-ion and Na-ion batteries are promising systems for powering electric vehicles and grid storage. Layered 3d transition metal oxides AxTMO2 (A = Li, Na; TM = 3d transition metals; 0<x≤2) have drawn extensive attention as cathode materials due to their exceptional energy densities. However, they suffer from several technical challenges caused by crystal structure degradation associated with TM ions migration, such as poor cycling stability, inferior rate capability, significant voltage hysteresis, and serious voltage decay. Aiming to tackle these challenges, this review provides an in-depth discussion and comprehensive understanding of the TM ions migration behaviors in AxTMO2. First, the key thermodynamics and kinetics that impact TM ions migration are discussed, covering ionic radius, electronic configuration, crystal structure arrangement, and migration energy barrier. In particular, details are provided regarding the universal and specific migration characteristics of Ni, Co, Mn, Fe, Cr, and V ions in layered cathode materials. Subsequently, the impacts of these migrations on electrochemical performance are emphasized in terms of the fundamental science behind technical issues, and strategies to modulate TM ions migration for advanced cathode materials development are summarized. Besides, characterization techniques for probing the TM ions migration are present, like neutron diffraction (ND), scanning transmission electron microscopy (STEM), nuclear magnetic resonance (NMR), and others. Finally, future directions in this regard are comprehensively concluded. This review offers valuable insights into the basic design of advanced layered oxide cathode materials for Li-ion and Na-ion batteries.

Exploring molecule-surface interactions of urania via IR spectroscopy and density functional theory.

Within the framework of surface-adsorbate interactions relevant to chemical reactions of spent nuclear fuel, the study of actinide oxide systems remains one of the most challenging tasks at both the experimental and computational levels. Consequently, our understanding of the effect of their unique electronic configurations on surface reactions lags behind that of d-block oxides. To investigate the surface properties of this system, we present the first infrared spectroscopy analysis of carbon monoxide (CO) interaction with a monocrystalline actinide oxide, UO2(111). Using a monocrystalline form largely avoids issues related to super-stoichiometries (UO2+x) and makes the experimental data suitable for further theoretical studies. Our findings reveal that CO adsorbs molecularly and shows a pronounced blue shift of the vibrational frequency to 2160 cm-1 relative to the gas-phase value. Interpreted through density functional theory (DFT) at different levels of computation, results indicate that to accurately describe the interaction between the CO molecule and the surface, it is essential to consider hybrid functionals, the non-collinearity of uranium's local magnetic moments, and spin-orbit coupling. Moreover, an intense IR absorption band at 978 cm-1 emerged upon CO adsorption, tentatively attributed to the frequency shift of the O-U-O asymmetric stretch of the UO2(111) surface in the presence of adsorbed oxygen. This new band, together with the observation of the importance of the relativistic effects in determining the nature of the chemical bonding of CO, is poised to broaden our understanding of actinide surface reactions.

A trimetallic bismuth(I)-based allyl cation

The chemistry of low-valent bismuth compounds has recently unlocked new concepts in catalysis and unique electronic structure fundamentals. In this work, we describe the synthesis and characterization of a highly reduced bismuth salt featuring a cationic core based on three contiguous Bi(I) centres. The triatomic bismuth-based core exhibits an electronic configuration that mimics the canonical description of the archetypical carbon-based π-allyl cation. Structural, spectroscopic and theoretical analyses validate the unique π-delocalization between the bismuth’s highly diffused 6p orbitals, resulting in a bonding situation in which the three bismuth atoms are interconnected by two bonds, formally possessing a 1.5 bond order each. This electronic situation defines this complex as the heaviest and stable π-allyl cation of the periodic table. Furthermore, we demonstrate that the newly synthesized complex is able to act as a synthon for the transfer of a Bi(I) cation to forge other low-valent organobismuth complexes.

A Series of AnVIO22+ Complexes (An = U, Np, Pu) with N3O2-Donating Schiff-Base Ligands: Systematic Trends in the Molecular Structures and Redox Behavior.

In their + V and + VI oxidation states, actinide elements (U, Np, and Pu) are commonly encountered in characteristic linear dioxo structures, known as actinyl ions (AnO2n+; An = U, Np, Pu, n = 1, 2). A systematic understanding of the structural and redox behavior of AnVO2+/AnVIO22+ complexes is expected to provide valuable information for controlling the behavior of An elements in natural environments and in nuclear fuel cycles while enabling the development of spintronics and new reactivities that utilize the anisotropic spin of the 5f electrons. However, systematic trends in the behavior of AnVO2+/AnVIO22+ complexes remain poorly understood. The [AnV/VIO2(saldien)]-/0 complexes (saldien2- = N,N'-disalicylidenediethylenetriamine) studied here offer a promising avenue for advancing our understanding of this subject. The molecular structures of a series of [AnVIO2(saldien)] complexes were found to exhibit notable similarities through these An elements with minor, but still significant, contributions from the actinide contraction. The redox potentials of the [AnV/VIO2(saldien)]-/0 couples clearly increase from U to Np, followed by a subsequent decrease from Np to Pu (-1.667 V vs Fc0/+ for [UV/VIO2(saldien)]-/0, -0.650 V for [NpV/VIO2(saldien)]-/0 and -0.698 V for [PuV/VIO2(saldien)]-/0). Such a difference can be explained in terms of the difference in character of the electronic configuration of the + VI oxidation state. A series of these redox trends was also successfully reproduced by DFT-based calculations. These findings provide valuable information for controlling the oxidation states of the An elements.

Decoupling many-body interactions in the CeO2(111) oxygen vacancy structure with statistical learning and cluster expansion.

Oxygen vacancies (VO's) are of paramount importance in influencing the properties and applications of ceria (CeO2). Yet, comprehending the distribution and nature of VO's poses a significant challenge due to the vast number of electronic configurations and intricate many-body interactions among VO's and polarons (Ce3+ ions). In this study, we established a cluster expansion model based on first-principles calculations and statistical learning to decouple the interactions among the Ce3+ ions and VO's, thereby circumventing the limitations associated with sampling electronic configurations. By separating these interactions, we identified specific electronic configurations characterized by the most favorable VO-Ce3+ attractions and the least favorable Ce3+-Ce3+/VO-VO repulsions, which are crucial in determining the stability of vacancy structures. Through more than 108 Metropolis Monte Carlo samplings of VO's and Ce3+ ions in the near surface of CeO2(111), we explored potential configurations within an 8 × 8 supercell. Our findings revealed that oxygen vacancies tend to aggregate and are abundant in the third oxygen layer with an elevated VO concentration primarily due to extensive geometric relaxation, an aspect previously overlooked. This work introduces a novel theoretical framework for unraveling the complex vacancy structures in metal oxides, with potential applications in redox and catalytic chemistry.

Controlling orbital ordering of intergrowth structures with flat [Ag(II)F2] layers to mimic oxocuprates(II).

Based on density functional theory calculations, we propose a new pathway toward compounds featuring flat [AgF2] layers which mimic [CuO2] layers in high-temperature oxocuprate superconductor precursors. Calculations predict the dynamic (phonon) and energetic stability of the new phases over diverse substrates. For some compounds with ferro orbital ordering, we find a gigantic intrasheet superexchange constant of up to -211 meV (DFT+U) and -256 meV (SCAN), calculated for hypothetical (CsMgF3)2KAgF3 intergrowth. Semiempirical calculations show that at optimum doping, the expected superconducting critical temperature should reach 200 K. The partial substitution of K+ with Ba2+ leads to noticeable electron doping of the [AgF2] sublattice, as revealed by progressive population of the upper-Hubbard band. On the other hand, modest 10-15% hole-doping through partial substitution of Mg2+ with Li+, primarily leads to the depopulation of p(z) orbitals of apical F atoms. We also find structures with an undesired antiferrodistortive structural ordering and discuss the structural factors that determine the transition from buckled to flat planes and from different types of orbital ordering using the Landau theory of phase transitions.

Duality of electron localization and configuration admixing for d/f electrons in two ordered cerium-nickel intermetallic compounds: Density functional theory merged with a two-impurity model

Duality of electron localization and configuration admixing for d/f electrons in two ordered cerium-nickel intermetallic compounds: Density functional theory merged with a two-impurity model

Ru2Ptx/AC catalysts with tunable electronic configurations for in-situ hydrogenolysis of glycerol

Ru2Ptx/AC catalysts with tunable electronic configurations for in-situ hydrogenolysis of glycerol

D-band state control engineering over ZnIn2S4 for enhanced photoreduction of CO2 to CH4.

Metal-based photocatalysts with d10 electronic configurations exhibit good photocatalytic performance due to strong band edge dispersion, however, the weak bonding between d10 metal sites and CO2 through 2p-3d orbital hybridization limits their activity and selectivity for CO2 to CH4 conversion. Herein, a strategy for modulating the d-band center is proposed to promote the formation of CH4 in the photocatalytic CO2 reduction process. In a model system taking ZnIn2S4 (ZIS) as photocatalysts, highly thermodynamically electronegative elements (such as Bi, Cu, and Co) are doped to upshift the d-band center of ZIS, enhance the selectivity and yield of CH4. In the absence of cocatalysts or photosensitizers, the CO2 photoreduction products of all doped ZIS samples shifts from pure CO to a mixture of CO and CH4, with CH4 being the predominant product. Among all samples, Bi-doped ZnIn2S4 (Bi-ZIS) demonstrates the highest performance, achieving a CH4 selectivity of 63.68% and a high evolution rate of 21.07µmol·g-1·h-1 during visible-light-driven CO2 reduction. Density functional theory (DFT) calculations indicate that doping highly electronegative elements can modulate the electron cloud distribution of ZIS, thereby raising its d-band center. This shift reduces the energy barrier for CO2 photoreduction to CH4, enhancing the binding energy between active sites and intermediates (such as *OCH2 and *OCH3), facilitating the formation of CH4. Consequently, this study not only validates the effectiveness of the d-band center modulation strategy but also offers a novel perspective for optimizing the activity and product selectivity of d10 metal-based photocatalysts in CO2RR.

Rocksalt-type heavy rare earth monoxides TbO, DyO, and ErO exhibiting metallic electronic states and ferromagnetism.

Solid-phase rare earth monoxides have been recently synthesized via thin film epitaxy. However, it has been difficult to synthesize heavy rare earth monoxides owing to their severe chemical instability. In this study, rocksalt-type heavy rare earth monoxides REOs (RE = Tb, Dy, Er) were synthesized for the first time, as single-phase epitaxial thin films. The REOs were characterized by hard X-ray photoemission spectroscopy, X-ray absorption spectroscopy, resonant photoemission spectroscopy, and magnetization measurements. These REOs showed metallic electronic states with the almost localized 4f states, indicating the 4fn5d1 electronic configurations of Tb, Dy, and Er ions. X-ray magnetic circular dichroism measurements of TbO evidenced the magnetic ordering of the 4f spins below the Curie temperature (TC). The TC was evaluated to be 233 K for TbO, 142 K for DyO, and 88 K for ErO, where the TC decreased with the 4f electron number, approximately proportional to the de Gennes factor.

Analytical nuclear gradient and derivative coupling theories for multireference perturbation methods.

Electron correlations should be appropriately included in quantum chemistry calculations to accurately describe the energy and wave functions. In multiconfigurational methods, the reference functions are written as linear combinations of multiple electronic configurations to describe static correlations. Using the multiconfigurational reference functions, it is also possible to correct for dynamical correlations using various methods. Geometry optimizations and dynamics simulations are among the most prominent applications of quantum chemistry methods. Such applications become much more straightforward when analytical nuclear gradients are available. Many efficient algorithms for computing analytical nuclear gradients and derivative coupling using multireference perturbation theories (MRPTs) have recently been developed. This work aims to provide a comprehensive and easy-to-follow review of analytical gradient theories and the properties of methods for obtaining analytical gradients and derivative coupling methods using MRPTs. We also briefly review the practical applications of these methods in performing nonadiabatic dynamics simulations.

Unveiling the molecular mechanism of Mn and Zn-catalyzed Ullmann-type C-O cross-coupling reactions.

A detailed theoretical study delving into the molecular mechanisms of the Ullmann-type O-arylation reactions catalyzed by manganese and zinc metal ions has been investigated with the aid of the density functional theory (DFT) method. In contrast to the redox-active mechanisms proposed for classical Ullmann-type condensation reaction, a redox-neutral mechanism involving σ-bond metathesis emerged as the most appealing pathway for the investigated high-valent Mn(II) and Zn(II)-catalyzed O-arylation reactions. The mechanism remains invariant with respect to the nature of the central metal, ligand, base, etc. This unusuality in the mechanism has been dissected by considering three cases: ligand-free and ligand-assisted Mn(II)-catalyzed O-arylation reaction and ligand-assisted Zn(II)-catalyzed O-arylation reactions. In each class, a metal phenoxide species was identified as the active catalyst. The unusual mechanistic trends observed in these C-O cross-coupling reactions could be attributed to the stable electronic configurations (d5, d10) combined with the higher oxidation states of the catalytic metal centers (Mn(II), Zn(II)). The exploration into the electronic effects of functional groups in controlling the reaction feasibility within each metal variant disclosed a consistent trend irrespective of the transition metal catalyst involved in the reaction. It was found that the introduction of electron-withdrawing groups at the para-position of organic halide lowers the energy of their lowest unoccupied molecular orbitals (LUMO), thereby lowering the HOMO-LUMO gap between the coupling partners. This study thereby revealed a comprehensive understanding of the fundamental mechanisms exhibited by high-valent first-row transition metal catalysts that could foster the development of eco-friendly protocols for preparing biaryl ether moieties.