Spin Density Calculations Research Articles

Expanding the Landscape of Phosphorous‐Based Open Shell Species: Stable Mono‐, Di‐, and Trianionic Radicals Based on a Contorted Triphosphaalkene

AbstractThe stepwise reduction of the highly contorted truxene‐based triphosphaalkene 1 using KC8 led to the isolation of mono‐, di‐, and tri‐anionic species. The solid‐state molecular structures of mono‐ and diradical anionic species were elucidated by single crystal X‐ray diffractions, revealing elongated P−C bonds and a pronounced “indene” aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open‐shell electronic configuration of both the diradical and triradical species—an observation unprecedented in any previously reported phosphorous‐based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34 % each), with a minor contribution from the third phosphorous (0.13 %), while the trianion demonstrates a uniform distribution of spin density (~30 %) across each phosphorous atom.

Expanding the Landscape of Phosphorous-Based Open Shell Species: Stable Mono-, Di-, and Trianionic Radicals Based on a Contorted Triphosphaalkene.

The stepwise reduction of the highly contorted truxene-based triphosphaalkene 1 using KC8 led to the isolation of mono-, di-and tri-anionic species. The solid-state molecular structures of mono- and diradical anionic species were elucidated by single crystal X-ray diffractions, revealing elongated P-C bonds and a pronounced "indene" aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open-shell electronic configuration of both the diradical and triradical species-an observation unprecedented in any previously reported phosphorous-based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34% each), with a minor contribution from the third phosphorous (0.13%), while the trianion demonstrates a uniform distribution of spin density (~30%) across each phosphorous atom.

Synergistic effects of vacancy and doping at Ge sublattices on the electronic and magnetic properties of new Janus Ge2PAs monolayer

Recently, 2D materials based on IV-V group have attracted great attention because of their interesting physical properties. In this work, Janus Ge2PAs monolayer with good stability is predicted using first-principles calculations. Our simulations assert its non-magnetic semiconductor nature with an indirect band gap of 1.11(1.75)eV obtained by PBE(HSE06)-based calculations. Further, vacancy defects and doping with transition metals (TMs = Cr and Mn) are explored in order to induce novel physical aspects. It is found significant magnetization of Janus Ge2PAs monolayer induced by Ge vacancies with total magnetic moments between 1.58 and 1.97 μB, where magnetism is produced mainly by atomic species around the defect sites. Herein, single Ge vacancy metalizes the monolayer, while the half-metallicity is obtained by creating a pair Ge vacancies. Regardless doping site, feature-rich diluted magnetic semiconductor and half-metallic behaviors are also obtained in Janus Ge2PAs monolayer by doping with Cr and Mn atom, respectively. In these case, TM impurities originate mainly the system magnetism with total magnetic moments between 2.00 and 3.03 μB. In addition, the coexistence of Ge vacancy and doping is also investigated. The calculated spin density shows an antiparallel spin orientation of Cr dopant and its neighboring atoms, meanwhile a parallel spin orientation is observed for Mn impurity and its neighboring atoms. Consequently, small total magnetic moment of 0.53 μB is obtained by the synergistic effects of doping with Cr and Ge vacancy, meanwhile the coexistence of Mn dopant and Ge vacancy generates a larger value of 4.88/4.89 μB. In all cases, the origin of electronic and magnetic properties is unraveled. Our results introduce new prospective spintronic 2D materials made from a new Janus Ge2PAs monolayer.

Advanced Molecular Design for Efficient Multicolor Electrochemiluminescence and Amplified Spontaneous Emission Based on Tetra‐BF2 Complexes

AbstractAdvanced organoboron dyes, incorporating tetra‐boron difluoride (tetra‐BF2) moieties, are developed, demonstrating efficient electrochemiluminescence (ECL) emissions in the green to orange regions through direct ion annihilation. By introducing diverse alkyl modifications in the molecules, luminescence color tuning is achieved via alterations in conjugation and bending angle. A photoluminescence quantum yield of 100% in dilute solutions is successfully achieved. Notably, the introduction of alkyl groups to the methine side stabilizes the radical ionic state, resulting in a high ECL efficiency of 74% through an efficient radical‐ion annihilation pathway. The key factor is that the energy of the annihilation reaction exceeds the S1 energy required for luminescence. Spin density calculations further elucidate the substituent effects on the radical ions of complexes. Moreover, the lasing properties of these materials in the solution‐processed blend films are investigated, revealing a low amplified spontaneous emission (ASE) threshold (Eth) of 6.40 ± 0.24 µJ cm−2, which is notably lower among organic laser materials. This is attributed to their large Stokes shifts and high quantum yield. The excellent ECL and ASE performances establish these materials as a valuable addition to the existing library of organoboron dyes, offering fresh insights into the development of organic solid‐state lasers.

On the energetic and magnetic stability of potassium atomic clusters doped by yttrium.

The abstract should be a single paragraph which summarises the content of the article. This study utilizes density functional theory (DFT) calculations to explore the energetic and magnetic stability of neutral and charged potassium (K) clusters doped with yttrium (Y). We aim to elucidate the influence of Y doping on the energetics and structures of these clusters, comparing them to undoped K clusters. Ground states of 64 polyhedral structures, all of them encapsulating at least one Y atom, were obtained. Y doping generally increased the spin magnetic moment, with charged clusters exhibiting the highest values. Notably, the K12Y+ cluster, possessing an icosahedral geometry and a magnetic moment of 6μB, is classified as a magnetic superatom. Additionally, we identified 14 superatoms with high magnetic robustness. The density of states (DOS) and spin density calculations additionally highlighted the substantial role played by yttrium in the electronic density of the electrons responsible for inducing magnetism in these clusters.

Study of curie temperaure, spin polarization, ferromagnetism and transport behavior of Ba2CrXO6 (X = Ta, W, Re, Os) for spintronic

The double perovskites (DPs) have become emerging aspirant for spintronic technology because of their stable, and multifunctional properties. Here in present article, the role 5d-electrons of Ta, W, Re, and Os in ferromagnetism, and thermoelectric behavior has been illustrated briefly. The ideal values of tolerance factor, formation energy and phonons dispersions are reported for structural, thermodynamic, and lattice dynamic stabilities. The higher Curie temperature and spin polarization has been addressed by Heisenberg model and spin density calculations. The ferromagnetism has been explained by the metallic and insulating channels of spin up and spin down configuration through hybridization, exchange energies, and exchange constants. The shifting of magnetic moments from Cr and X sites to Ba, O and interstitial sites ensures the exchange coupling due to spin of electrons rather than clustering. Furthermore, thermoelectric effect on the spin degree of electrons and transport characteristics are calculated by BoltzTraP code.

Role of π-Radical Localization on Thermally Stable Cross-Links Between Polycyclic Aromatic Hydrocarbons.

The thermal stability of cross-links between polycyclic aromatic hydrocarbons (PAHs) is critical for understanding the formation of soot pollutants, graphite, and carbon blacks. Recently, a variety of different π-radicals have been directly imaged and suggested to enable thermally stable bonding; however, a systematic study of reactivity has been lacking. In this work, we use density functional theory to study the reactivity of PAH π-radicals. The Mulliken spin densities are initially used to categorize the different classes of localization, and the bond energy is computed to determine the degree of localization required for thermal stability. The results showed that the bond energies of PAHs are strongly correlated with the calculated spin densities, but bond energies do not exist with the bond lengths due to significant rearrangement and steric effects during bond formation. A threshold for π-radical localization is suggested that will be stable in combustion and pyrolysis environments of ρMα ≥ 0.5. Finally, the formation of multicenter bonds between localized and delocalized π-radicals was investigated using the nudge elastic band (NEB) scan, and it was found that only delocalized π-radicals provided local energy minima. These results show that the localization of π-radicals is critical for the formation of thermally stable single-center bonds between aromatic radicals.

N‐(aminobenzyliden)phthalimides as a New Redox Mediator Family for the Selective Indirect Reduction of Benzyl or Allyl Halides

AbstractThe chemical stability of the electrogenerated radical anion of N‐(aminobenzyl) phthalimide 1 in aprotic organic media at room temperature is reported in this work. The redox couples 1/1⋅− and its imine precursor 2/2⋅− can carry out reductive redox catalysis of benzyl or allyl halides indirectly. This reaction gives easy access to reactive alkyl radicals, which in the presence of diethyl fumarate yields 2‐benzylsuccinate diethyl ester in moderate yields; this reaction is unattainable by direct electrochemical reduction. Spin density calculations at the DFT level of theory showed that the spin density of 1⋅− and 2⋅− is located on the phtalimide ring, and a dimeric association was evidenced (Eint=23.47 kcal/mol and Eint=80.42 kcal/mol respectively), via π−π stacking interactions. The redox mediators presented here showed good functional group selectivity, redox potential tunability and easy preparation from readily available commercial materials with excellent yields.

Photochemical Oxidation of Dimethyl Sulfide with Triplet Nitro Compounds

The mechanism of oxygen atom transfer between triplet molecules of a nitro compound and dimethyl sulfide is considered. This reaction pathway can be one of the possible routes in the reaction of photochemical oxidation of the sulfur compound. Quantum-chemical modeling has shown the feasibility of such a reaction as having a fairly low activation energy. The transition states of the reaction have almost the same structure in various solvents. The calculation of spin densities and charges on atoms in transition states hasshown no significant charge separation. This finding is also confirmed by calculation of the activation parameters of the oxygen transfer reaction involving various solvents. The activation energies remain almost unchanged with an increase in the solvent permittivity. All the data obtained suggest the radical mechanism of oxygen atom transfer with the participation of the triplet nitro compound.

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

Spin-related electronic pathway through single molecule on Au(111)

Spin properties of organic molecules have attracted great interest for their potential applications in spintronic devices and quantum computing. Fe-tetraphenyl porphyrin (FeTPP) is of particular interest for its robust magnetic properties on metallic substrates. FeTPP is prepared in vacuum via on-surface synthesis. Molecular structure and spin-related transport properties are characterized by low-temperature scanning tunneling microscope and spectroscopy at 0.5 K. Density functional theory calculations are performed to understand molecular adsorption and spin distribution on Au(111). The molecular structure of FeTPP is distorted upon adsorption on the substrate. Spin excitations of FeTPP are observed on the Fe atom and high pyrrole groups in differential conductance spectra. The calculated spin density distribution indicates that the electron spin of FeTPP is mainly distributed on the Fe atom. The atomic transmission calculation indicates that electrons transport to substrate is mediated through Fe atom, when the tip is above the high pyrrole group.

DFT study on CH⋯O, CH···SCN and S···π interaction energies in three dinuclear mixed valence cobalt(III/II) complexes with secondary diamine ligands having inner N2O2 and outer O4 compartments

Three dinuclear cobalt(III/II) mixed valence reduced Schiff base complexes, [(N3)CoIIIL(μ-O2CR1)CoII(N3)] (1), [(SCN)CoIIIL(μ-O2CR2)CoII(NCS)] (2) and [(SCN)CoIIIL(μ-O2CR3)CoII(NCS)] (3) {H2L= (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol); R1CO2H = 4-methyl-3-nitrobenzoic acid; R2CO2H = benzoic acid; R3CO2H = 3-methyl-4-nitrobenzoic acid} have been synthesized and characterized by elemental analysis and spectral study. X-ray diffraction analysis was used to determine the structures of all three complexes. Spin density calculations have been used to determine the location of the paramagnetic cobalt(II) center in each of the dinuclear complexes. Moreover, several supramolecular assemblies (formed by CH⋯O, CH···SCN and S··· π and other interactions) observed in the solid state of the three complexes involving the pseudohalide as electron donors have been analysed using DFT calculations, molecular electrostatic potential (MEP) surfaces and characterized using the noncovalent interaction plot (NCI Plot) index.

Spin-density calculation via the graphical unitary group approach

In this work we discuss the calculation of the spin-density matrix from fundamental spin principles as implemented in the COLUMBUS Program System employing the graphical unitary group approach (GUGA). First, a general equation for the spin-density matrix is derived in terms of the one-and two-particle reduced density matrices, quantities that are spin-independent and readily available within the GUGA formalism. Next, the evaluation of this equation using the Shavitt loop values is discussed. Finally, the spatially resolved counterpart of the spin-density matrix, the spin distribution, is calculated for the phenalenyl radical and structures produced by heteroatoms with mono- and di-substitutions. The physical meaning of the spin-density along with its computational description using various methods is discussed putting special emphasis on negative contributions to the spin-density and their quantification via a spin-promotion index.

Field-induced single-molecule magnet behaviour in a series of dinuclear cobalt(III,II) complexes

We present the synthesis, structure and magnetic characterization of four dinuclear cobalt(III,II) complexes: [(NCS)CoIII(Ln)(µ–OAc)CoII(NCS)]·G, with n/G = 1/CH3OH (1), 2/CH3CN (2), 3/- (3) and 4/CH3OH (4), being H2Ln, four closely related reduced Schiff base ligands: H2L1 = (1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol), H2L2 = (1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol), H2L3= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-methoxyphenol) and H2L4= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-ethoxyphenol). The single crystal X-ray structures of complexes 1–4 show that both cobalt centres in the four complexes adopt a distorted octahedral geometry with Co(III) and Co(II) centres residing at inner N2O2 and outer O4 pockets of the reduced Schiff base, respectively. Magnetic measurements show that all complexes behave as Co(II) monomers, confirming the presence of diamagnetic low spin Co(III) ions, which have also been supported by the spin-density calculation using Density Functional Theory. Additionally, complexes 1–4 show a field-induced slow relaxation of the magnetization at low temperatures that follow direct and Raman mechanisms.

Synthesis of complex bicyclic scaffolds by intermolecular photosensitized dearomative cycloadditions of activated alkenes and naphthalenes.

The rapid buildup of molecular complexity from simple precursors is a key goal in organic chemistry. One strategy to achieve this is through a dearomative cycloaddition wherein a 2D arene and alkene is converted to a 3D structure. In many cases this type of reactivity has been achieved with photochemistry. Despite the prospect of such a reaction, most known variants are intramolecular, which greatly limits the scope of chemical space that can be accessed. Intermolecular variants are known but are generally limited to heterocyclic systems such as indoles or quinolines. Herein, a method for intermolecular dearomative cycloaddition of simple naphthalenes with alkenes is presented. The reactions operate by a photoinduced sensitization of the arene. The bridged bicyclic products are generated with control of regiochemistry and function for a range of alkenes. In addition, the products can serve as useful intermediates as demonstrated in the synthesis of a biologically active benzazapine analog. Mechanistic studies are also included, which support reaction via a triplet excited state and that the selectivity can be rationalized by spin-density calculations.

Mn12 -Acetate Complexes Studied as Single Molecules.

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn12 coordination clusters of general formula [MnIII 8MnIV 4O12(RCOO)16(H2O)4] had been exemplified by bulk samples of the archetypal [MnIII 8MnIV 4O12(CH3COO)16(H2O)4] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn12 system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn12O12(CH3COO)15(CH3CN)]+ (1) by gas phase X‐ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn12O12(CH3COO)15(CH3CN)]+ (1), [Mn12O12(CH3COO)16] (2), [Mn12O12(CH3COO)16(H2O)4] (3), and the complex in bulk geometry [MnIII 8MnIV 4O12(CH3COO)16(H2O)4] (5). The found magnetic fingerprints – experiment and theory alike – are of a remarkable robustness: The MnIV 4 core bears almost no magnetic anisotropy while the surrounding MnIII 8 ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn12 core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects.

Low temperature activation of inert hexagonal boron nitride for metal deposition and single atom catalysis

Hexagonal boron nitride (hBN) has long been considered chemically inert due to its wide bandgap and robust covalent bonds. Its inertness hinders hBN from functionalization for energy conversion applications. A question arising is whether it is possible to make hBN chemically reactive. Here, we report cryomilling in liquid N2, as an effective strategy to activate the chemical reactivity of hBN by engineering different vacancies to produce defective-BN (d-BN). The local reactivity of the vacancies is probed by photoluminescence (PL) emissions and electron spin resonance spectroscopy (ESR). Density functional theory calculations reveal that the formation of different vacancies with/without oxygen cause the creation of mid-gap states that are responsible for the PL emissions in the visible region. These vacancies also generate localized free radicals which are both theoretically and experimentally confirmed by spin density calculations and ESR. Due to the vacancy induced free radicals and Fermi level shifts, d-BN can be controllably functionalized with single metal atoms by the spontaneous reduction of metal cations; mono-metallic or bi-metallic clusters can also be effectively reduced. As a proof of concept, the surface-bound metal nanostructures, especially substrate confined single metal atoms, exhibit improved hydrogen evolution catalytic performance, and can be further used for sensing, and quantum information.

Electron Distribution in 1,2,3-Benzotriazole and 1,2,3-Triazole Anion Radical Isomers: An EPR and DFT Study.

The anion radicals of N1- and N2-alkylbenzotriazoles and alkyltriazoles (alkyl = methyl or isopropyl) have been generated by low-temperature potassium metal reduction in tetrahydrofuran. Electron paramagnetic resonance (EPR) analysis and density functional theory calculations reveal that the electron spin distribution within the triazole ring of these systems is markedly different. The magnitude of the electron-nitrogen couplings along with the calculated spin densities reveals that the N2-alkylbenzotriazole and N2-alkyltriazole anion radicals have significantly greater electron spin residing within the N3 portion of the triazole ring compared with that of the respective N1 isomers. These differences impact the overall geometry of the triazole ring where both N2-isomers lose planarity upon reduction. Experimental and computational results reveal that the N2-methyltriazole anion radical has the largest concentration of electron spin residing in the N3 moiety compared to that of the other three anion radicals studied. Significant anisotropic line broadening is observed in the EPR spectrum of the N2-methyltriazole anion radical, which is a consequence of the large nitrogen hyperfine couplings and sufficiently slow rotational motion of this species in solution.

Graphene oxide @ nickel phosphate nanocomposites for photocatalytic hydrogen production

The graphene oxide @nickel phosphate (GO:NPO) nanocomposites (NCs) are prepared by using a one-pot in-situ solar energy assisted method by varying GO:NPO ratio i.e. 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, and 2.00 without adding any surfactant or a structure-directing reagent. As produced GO:NPO nanosheets exhibited an improved photocatalytic activity due to the spatial seperation of charge carriers through interface, where photoinduced electrons transferred from NiPO4 to the GO sheets without charge-recombination. Out of the series, the system 1.00 GO:NPO NC show the optimum hydrogen production activity (15.37 μmol H2 h−1) towards water splitting under the visible light irradiation. The electronic environment of the nanocomposite GO-NiO6/NiO4-PO4 elucidated in the light of advance experimental analyses and theoretical DFT spin density calculations. Structural advanmcement of composites are well correlated with their hydrogen production activity.

Theoretical Assessment of Hinge-Type Models for Electron Donors in Reaction Centers of Photosystems I and II as well as of Purple Bacteria

Hinge-type molecular models for electron donors in reaction centers of Photosystems I and II and purple bacteria were investigated using a two-state computational approach based on frozen-density embedding (FDE). This methodology, dubbed FDE-diab, is known to avoid consequences of the self-interaction error as far as intermolecular phenomena are concerned, which allows a prediction of qualitatively correct spin densities for large biomolecular systems. The calculated spin density distributions are in a good agreement with available experimental results and demonstrated a very high sensitivity to changes in the relative orientation of cofactors and amino acid protonation states. This allows a validation of the previously proposed hinge-type models providing hints on possible protonation states of axial histidine molecules.