Search

The regulation of solution pH on the structural and optical properties of peptide self‐assemblies remains a critical yet unresolved issue in peptide research. This study investigates the heptapeptide Ac‐IHIHIQI‐NH2 and its intrinsic fluorescence across a range of pH levels, demonstrating that variations in pH lead to significant changes in the morphology of the self‐assembled structures. While the position of the fluorescence emission remains constant—due to the stability provided by the hydrogen bonding network of the peptide backbone—the intensity of the fluorescence exhibits a direct correlation with the degree of self‐assembly. This finding underscores a dynamic relationship between structural morphology and optical properties. Notably, the ability of the peptide to self‐assemble under diverse pH conditions is a novel observation that contrasts with previously reported literature. By employing a computationally driven approach, complemented by rigorous experimental validation, this work establishes a new paradigm for studying complex interacting systems such as peptide self‐assembly. Our findings enhance the understanding of how environmental factors influence peptide behavior and pave the way for the design of innovative peptide‐based materials with tunable optical characteristics, with potential applications in bioluminescent probes and diagnostic tools for neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

The development of molecular switches with tunable properties has garnered considerable interest over several decades. A novel spin‐crossover (SCO) material based on iron(II) complexes incorporating 4‐acetylpyridine (4‐acpy) and [Hg(SCN)4]2− anions was synthesized and formulated as [Fe(4‐acpy)2][Hg(μ‐SCN)4] (1). Compound 1 is crystallized in a three‐dimensional network in the non‐centrosymmetric orthorhombic space group Pna21 with two octahedral [Fe(4‐acpy)2(NCS)4] entities featuring two distinct Fe centers (Fe1 and Fe2). Crystallographic, magnetic, and Mössbauer measurements reveal an incomplete SCO exclusively at Fe2, with transition temperature T1/2≈102 K. Photomagnetic studies conducted at 10 K with lasers ranging from 405 to 1310 nm evidence light‐induced excited spin‐state trapping (LIESST) and reverse‐LIESST effects, with a unique near‐infrared‐responsive LIESST phenomenon at 1064 and 1310 nm. Advanced photocrystallographic studies at 40 K provide precise structural evidence for these metastable states. The optical and vibrational properties consistently corroborate with magnetic and photomagnetic studies. Additionally, temperature‐ and light‐dependent terahertz (THz) absorptions are associated with phonon vibrations around Fe2 centers, through SCO behavior, as supported by ab initio calculation. The Fe(II)−Hg(II) systems can be promising benchmarks for exploring synergistic switching effects in structural, magnetic, and spectroscopic properties. [ABSTRACT FROM AUTHOR]

At the air–water interface, many reactions are accelerated, sometimes by several orders of magnitude. This phenomenon has proved to be particularly important in water microdroplets, where the spontaneous oxidation of many species stable in bulk has been experimentally demonstrated. Different theories have been proposed to explain this finding, but it is currently believed that the role of interfacial electric fields is key. In this work, we have carried out a quantum chemistry study aimed at shedding some light on this question. We have studied two prototypical processes in which a hydroxide anion transfers its excess electron to either the water environment or a dioxygen molecule. To model the interface, we use a cluster of 21 water molecules immersed in an electric field, and we examine the energetics of the studied reactions as a function of field magnitude. Our results reveal that electric fields close to those estimated for the neat air–water interface (∼0.15 V ⋅ Å−1) have a moderate effect on the reaction energetics and that much stronger fields (>1 V ⋅ Å−1) are required to get spontaneous electron transfer. Therefore, the study suggests that additional factors such as an excess charge in microdroplets need to be considered for explaining the experimental observations. [ABSTRACT FROM AUTHOR]

A long‐standing question in electron transfer research concerns the number and identity of collective nuclear motions that drive electron transfer or localisation. It is well established that these nuclear motions are commonly gathered into a so‐called electron transfer coordinate. In this theoretical study, we demonstrate that both anti‐symmetric and symmetric vibrational motions are intrinsic to bridged systems, and that both are required to explain the characteristic shape of their intervalence charge transfer bands. Using the properties of a two‐state Marcus–Hush model, we identify and quantify these two coordinates as linear combinations of normal modes from ab initio calculations. This quantification gives access to the potential coupling, reorganization energy and curvature of the potential energy surfaces involved in electron transfer, independent of any prior assumptions about the system of interest. We showcase these claims with the Creutz–Taube ion, a prototypical Class III mixed valence complex. We find that the symmetric dimension is responsible for the asymmetric band shape, and trace this back to the offset of the ground and excited state potentials in this dimension. The significance of the symmetric dimension originates from geometry dependent coupling, which in turn is a natural consequence of the well‐established superexchange mechanism. The conceptual connection between the symmetric and anti‐symmetric motions and the superexchange mechanism appears as a general result for bridged systems. [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]

The highly selective hydrogenation to remove olefins is a significant refining approach for the reformate. Herein, a library of transition metal for reformate hydrogenation is tested experimentally to validate the predictive level of catalytic activity from our theoretical framework, which combines ab initio calculations and microkinetic modeling, with consideration of surface H‐coverage effect on hydrogenation kinetics. The favorable H coverage of specific alloy surface under relevant hydrogenation condition, is found to be determined by its corresponding alloy composition. Besides, olefin hydrogenation rate is determined as a function of two descriptors, i.e. H coverage and binding energies of atomic hydrogen, paving the way to computationally screen on metal component in the periodic table. Evaluation of 172 bimetallic alloys based on the activity volcano map, as well as benzene hydrogenation rate, identifies prospective superior candidates and experimentally confirms that Zn3Ir1 outperforms pure Pd catalysts for the selective hydrogenation refining of reformate. The insights into H‐coverage‐related microkinetic modelling have enabled us to both theoretically understand experimental findings and identify novel catalysts, thus, bridging the gap between first‐principle simulations and industrial applications. This work provides useful guidance for experimental catalyst design, which can be easily extended to other hydrogenation reaction. [ABSTRACT FROM AUTHOR]

By reaction of sodium electride or NaC2H with the anhydrous sodium salt of propiolic acid, Na(OOC−C≡C−H), in liquid ammonia crystalline powders of Na2C3O2 were obtained. The structure analysis based on synchrotron powder diffraction data revealed that Na2C3O2 crystallizes in a monoclinic unit cell (I2/a, Z=4) exhibiting the elusive Y‐shaped −C≡C−COO− anion, which is unprecedented in a crystalline compound up to now. IR/Raman and solid‐state NMR spectroscopic investigations with assignments supported by DFT‐based ab initio calculations confirm this finding. Reaction with sodium electride led to a higher crystallinity of the product, but additionally a by‐product apparently due to decomposition and polymerization of Na2C3O2 was formed. No such by‐product was observed in the reaction with NaC2H, which turned out to be a milder metalation route. However, the product of the latter reaction is less crystalline. [ABSTRACT FROM AUTHOR]

In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

The character of the electronic structure of acenes has been the subject of longstanding discussion. However, convincing experimental evidence of their open‐shell character has so far been missing. Here, we present the on‐surface synthesis of tridecacene molecules by thermal annealing of octahydrotridecacene on a Au(111) surface. We characterized the electronic structure of the tridecacene by scanning probe microscopy, which reveals the presence of an inelastic signal at 126 meV. We attribute the inelastic signal to spin excitation from the singlet diradical ground state to the triplet excited state. To rationalize the experimental findings, we carried out many‐body ab initio calculations as well as model Hamiltonians to take into account the effect of the metallic substrate. Moreover, we provide a detailed analysis of how the dynamic electron correlation and virtual charge fluctuation between the molecule and metallic surface reduces the singlet‐triplet band gap. Thus, this work provides the first experimental confirmation of the magnetic character of tridecacene. [ABSTRACT FROM AUTHOR]

Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photonics and spintronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self‐assembled thin film made of a carbazole di‐bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure–property relationships, resulting in a more efficient material design. [ABSTRACT FROM AUTHOR]

The purification of p‐xylene (pX) from its xylene isomers represents a challenging but important industrial process. Herein, we report the efficient separation of pX from its ortho‐ and meta‐ isomers by a microporous calcium‐based metal–organic framework material (HIAM‐203) with a flexible skeleton. At 30 °C, all three isomers are accommodated but the adsorption kinetics of o‐xylene (oX) and m‐xylene (mX) are substantially slower than that of pX, and at an elevated temperature of 120 °C, oX and mX are fully excluded while pX can be adsorbed. Multicomponent column breakthrough measurements and vapor‐phase/liquid‐phase adsorption experiments have demonstrated the capability of HIAM‐203 for efficient separation of xylene isomers. Ab initio calculations have provided useful information for understanding the adsorption mechanism. [ABSTRACT FROM AUTHOR]

Carbohydrates are the most abundant organic material on Earth and the structural "material of choice" in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom‐up engineering of carbohydrate materials demands an atomic‐level understanding of their molecular structures and interactions in condensed phases. Here, high‐resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three‐dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D‐ and L‐oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases. [ABSTRACT FROM AUTHOR]

Nanoconfinement effects on water dissociation and reactivity remain controversial, despite their importance to understand the aqueous chemistry at interfaces, pores, or aerosols. The pKw in confined environments has been assessed from experiments and simulations in a few specific cases, leading to dissimilar conclusions. Here, with the use of carefully designed ab initio simulations, we demonstrate that the energetics of bulk water dissociation is conserved intact to unexpectedly small length‐scales, down to aggregates of only a dozen molecules or pores of widths below 2 nm. The reason is that most of the free‐energy involved in water autoionization comes from breaking the O−H covalent bond, which has a comparable barrier in the bulk liquid, in a small droplet of nanometer size, or in a nanopore in the absence of strong interfacial interactions. Thus, dissociation free‐energy profiles in nanoscopic aggregates or in 2D slabs of 1 nm width reproduce the behavior corresponding to the bulk liquid, regardless of whether the corresponding nanophase is delimited by a solid or a gas interface. The present work provides a definite and fundamental description of the mechanism and thermodynamics of water dissociation at different scales with broader implications on reactivity and self‐ionization at the air‐liquid interface. [ABSTRACT FROM AUTHOR]

Ethylene epoxidation is industrially and commercially one of the most important selective oxidations. Silver catalysts have been state‐of‐the‐art for decades, their efficiency steadily improving with empirical discoveries of dopants and co‐catalysts. Herein, we perform a computational screening of the metals in the periodic table, identify prospective superior catalysts and experimentally demonstrate that Ag/CuPb, Ag/CuCd and Ag/CuTl outperform the pure‐Ag catalysts, while they still confer an easily scalable synthesis protocol. Furthermore, we show that to harness the potential of computationally‐led discovery of catalysts fully, it is essential to include the relevant in situ conditions e.g., surface oxidation, parasitic side reactions and ethylene epoxide decomposition, as neglecting such effects leads to erroneous predictions. We combine ab initio calculations, scaling relations, and rigorous reactor microkinetic modelling, which goes beyond conventional simplified steady‐state or rate‐determining modelling on immutable catalyst surfaces. The modelling insights have enabled us to both synthesise novel catalysts and theoretically understand experimental findings, thus, bridging the gap between first‐principles simulations and industrial applications. We show that the computational catalyst design can be easily extended to include larger reaction networks and other effects, such as surface oxidations. The feasibility was confirmed by experimental agreement. [ABSTRACT FROM AUTHOR]

LiI and LiBr have been employed as soluble redox mediators (RMs) in electrolytes to address the sluggish oxygen evolution reaction kinetics during charging in aprotic Li‐O2 batteries. Compared to LiBr, LiI exhibits a redox potential closer to the theoretical one of discharge products, indicating a higher energy efficiency. However, the reason for the occurrence of solvent deprotonation in LiI‐added electrolytes remains unclear. Here, by combining ab initio calculations and experimental validation, we find that it is the nucleophile IO3- ${{{\rm I}{\rm O}}_{3}^{-}}$ that triggers the solvent deprotonation and LiOH formation via nucleophilic attack, rather than the increased solvent acidity or the elongated C−H bond as previously suggested. As a comparison, the formation of BrO3- ${{{\rm B}{\rm r}{\rm O}}_{3}^{-}}$ in LiBr‐added electrolytes is found to be thermodynamically unfavorable, explaining the absence of LiOH formation. These findings provide important insight into the solvent deprotonation and pave the way for the practical application of LiI RM in aprotic Li‐O2 batteries. [ABSTRACT FROM AUTHOR]

Self‐assembly FeII complexes of phenazine (Phen), quinoxaline (Qxn), and 4,4′‐trimethylenedipyridine (Tmp) with tetrahedral building blocks of [HgII(XCN)4]2− (X=S or Se) formed six new high‐dimensional frameworks with the general formula of [Fe(L)m][Hg(XCN)4]⋅solvents (L=Phen, m/X=2/S, 1; L=Qxn, m/X=2/S, 2; L=Qxn, m/X=1/S, 3; L=Qxn, m/X=1/Se, 3‐Se; L=Tmp, m/X=1/S, 4; and L=Tmp, m/X=1/Se, 4‐Se). 1, 3, and 3‐Se show an intense sub‐terahertz (sub‐THz) absorbance of around 0.60 THz due to vibrations of the solvent molecules coordinated to the FeII ions and crystallization organic molecules. In addition, crystals of 1, 4, and 4‐Se display low‐frequency Raman scattering with exceptionally low values of 0.44, 0.51, and 0.53 THz, respectively. These results indicate that heavy metal FeII−HgII systems are promising platforms to construct sub‐THz absorbers. [ABSTRACT FROM AUTHOR]

The LiOH‐based cathode chemistry has demonstrated potential for high‐energy Li−O2 batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e− oxygen reduction, in which Li2O2 acts as intermediate in low water‐content electrolyte but LiHO2 as intermediate in high water‐content electrolyte. Besides, LiOH decomposes via 1 e− oxidation during charge, generating surface‐reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high‐potential charge plateau (1 e− water oxidation). At following cycles, these accumulated protons lead to a new high‐potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e− cathode chemistries in metal–air batteries. [ABSTRACT FROM AUTHOR]

The full separation of alkane isomers as a function of different degrees of branching remains a daunting challenge due to its stringent requirement with respect to pore dimensions of the adsorbents. In this work, we report a novel microporous coordination network built on calcium (II) and chloranilate. The compound has a flexible framework and exhibits temperature‐dependent adsorption behavior toward hexane isomers. At 30 °C, it accommodates substantial amounts of linear and monobranched hexanes but fully excludes their dibranched isomer, and at elevated temperatures such as 150 °C, it acts as a splitter for linear and branched alkanes. Its capability of efficient discrimination of hexane isomers as a function of branching is verified by experimental breakthrough measurements. Ab initio calculations have uncovered the underlying selective size‐exclusion separation mechanism. [ABSTRACT FROM AUTHOR]

A new class of beryllium‐boron clusters, beryllo‐borospherene, is described herein theoretically. When beryllium is gradually added to the B12 motif, it undergoes drastic structural modifications. The global minimum of the Be4B12+ cluster is an Archimedean beryllo‐borospherene in a 2A1 electronic ground state, composed of four boron triangles linked at each corner, resulting in a truncated tetrahedron with four B6 rings capped with four beryllium atoms. Beryllium forms strong bonding with the boron clusters through strong electrostatic and covalent interactions. For instance, the bonding between a beryllium atom and Be3B12 unit is best described as a Be+ fragment in a 2P excited state forming a strong and polarized electron‐sharing bond with Be3B12, followed by several dative interactions by employing its vacant s, p, and very high‐lying d orbitals. Counterintuitively, for an s‐block element, the p orbitals of beryllium are the most crucial atomic orbitals for bonding rather than s orbitals. [ABSTRACT FROM AUTHOR]

Although pyrazine‐linked hybrid ultramicroporous materials (HUMs, pore size <7 Å) are benchmark physisorbents for trace carbon dioxide (CO2) capture under dry conditions, their affinity for water (H2O) mitigates their carbon capture performance in humid conditions. Herein, we report on the co‐adsorption of H2O and CO2 by TIFSIX‐3‐Ni—a high CO2 affinity HUM—and find that slow H2O sorption kinetics can enable CO2 uptake and release using shortened adsorption cycles with retention of ca. 90 % of dry CO2 uptake. Insight into co‐adsorption is provided by in situ infrared spectroscopy and ab initio calculations. The binding sites and sorption mechanisms reveal that both CO2 and H2O molecules occupy the same ultramicropore through favorable interactions between CO2 and H2O at low water loading. An energetically favored water network displaces CO2 molecules at higher loading. Our results offer bottom‐up design principles and insight into co‐adsorption of CO2 and H2O that is likely to be relevant across the full spectrum of carbon capture sorbents to better understand and address the challenge posed by humidity to gas capture. [ABSTRACT FROM AUTHOR]

Zeolites have found tremendous applications in the chemical industry. However, the dynamic nature of their active sites under the flow of adsorbate molecules for adsorption and catalysis is unclear, especially in operando conditions, which could be different from the as‐synthesized structures. In the present study, we report a structural transformation of the adsorptive active sites in SAPO‐34 zeolite by using acetone as a probe molecule under various temperatures. The combination of solid‐state nuclear magnetic resonance, in situ variable‐temperature synchrotron X‐ray diffraction, and in situ diffuse‐reflectance infrared Fourier‐transform spectroscopy allow a clear identification and quantification that the chemisorption of acetone can convert the classical Brønsted acid site adsorption mode to an induced Frustrated Lewis Pairs adsorption mode at increasing temperatures. Such facile conversion is also supported by the calculations of ab‐initio molecular‐dynamics simulations. This work sheds new light on the importance of the dynamic structural alteration of active sites in zeolites with adsorbates at elevated temperatures. [ABSTRACT FROM AUTHOR]

C≡N bond scission can be a potential avenue for the functionalization of chemical bonds. We have conducted a computational study, using density functional theory (DFT) and ab initio multireference CASSCF methods, to unravel the intricate mechanistic pathways traversed in the copper‐promoted, dioxygen‐assisted reaction for the formation of aryl isocyanate species from aryl aldehyde. This aryl isocyanate species acts as an active species for C≡N bond cleavage of coordinated cyanide anion enabling nitrogen transfer to various aldehydes. Electronic structure analysis revealed that under all the reaction conditions radical‐based pathways are operative, which is in agreement with the experimental findings. The major driving force is a CuII/I redox cycle initiated by single‐electron transfer from the carbon center of the nitrile moiety. Our study reveals that the copper salts act as the "electron pool" in this unique nitrogen transfer reaction forming an aryl isocyanate species from aryl aldehydes. [ABSTRACT FROM AUTHOR]

By employing accurate state‐of‐the‐art many‐electron quantum‐chemistry methods, we establish that monocyclic carbon rings can accommodate Li guest atoms. The low‐lying electronic states of these endocircular systems are analyzed and found to include both charge‐separated states where the guest Li atom appears as a cation and the ring as an anion and encircled‐electron states where Li and the ring are neutral. The electron binding energies of the encircled‐electron states increase drastically at their highly symmetric equilibrium geometries with increasing size of the ring, and in Li@C24, this state becomes the ground state. Li is very weakly bound vertical to the rings in the low‐lying encircled‐electron states, hinting to van‐der‐Waals binding. Applcations are mentioned. [ABSTRACT FROM AUTHOR]

We assess the crucial role of tetrapyrrole flexibility in the CO ligation to distinct Ru‐porphyrins supported on an atomistically well‐defined Ag(111) substrate. Our systematic real‐space visualisation and manipulation experiments with scanning tunnelling microscopy directly probe the ligation, while bond‐resolving atomic force microscopy and X‐ray standing‐wave measurements characterise the geometry, X‐ray and ultraviolet photoelectron spectroscopy the electronic structure, and temperature‐programmed desorption the binding strength. Density‐functional‐theory calculations provide additional insight into the functional interface. We unambiguously demonstrate that the substituents regulate the interfacial conformational adaptability, either promoting or obstructing the uptake of axial CO adducts. [ABSTRACT FROM AUTHOR]

Herein, we investigate a novel set of polarizing agents—mixed‐valence compounds—by theoretical and experimental methods and demonstrate their performance in high‐field dynamic nuclear polarization (DNP) NMR experiments in the solid state. Mixed‐valence compounds constitute a group of molecules in which molecular mobility persists even in solids. Consequently, such polarizing agents can be used to perform Overhauser‐DNP experiments in the solid state, with favorable conditions for dynamic nuclear polarization formation at ultra‐high magnetic fields. [ABSTRACT FROM AUTHOR]

Keywords: electrochemistry; ferrocenate; ferrocene; organometallic chemistry; redox chemistry EN electrochemistry ferrocenate ferrocene organometallic chemistry redox chemistry 12632 12635 4 05/28/21 20210601 NES 210601 The recent discoveries of both dicationic and monoanionic ferrocene derivatives throw light on the effect of the substituents on the C SB 5 sb ring as well as the choice of redox agents and solvent system in the preparation of previously believed to be difficult synthetic targets. Electrochemistry, ferrocenate, ferrocene, organometallic chemistry, redox chemistry The realization that ferrocene in polar organic solutions could overcome liquid junction potential problems led to the use of the ferrocene/ferrocenium couple as an ideal internal standard in organometallic electrochemistry.[3] Although ferrocene can undergo reversible one- and two-electron oxidations as well as one-electron reduction, only the monocation (Fe SP III sp ) can be readily isolated. [Extracted from the article]

Atomic‐level control over the position and growth of a single and continuous metal chain is an ambitious goal that often requires complex and costly processes. Herein, we demonstrate that 1Pd‐DNA molecules, comprising a continuous single chain of PdII ions, can be prepared by a simple self‐assembly reaction between the complex [Pd(Cheld)(CH3CN)] (1Pd_CH3CN) (Cheld=chelidamic acid) and single‐stranded DNA homopolymers (ss‐DNA) containing adenine (A) or 7‐deazaadenine (X) bases. The single PdII‐base pairs [1Pd(N1‐A)] and [1Pd(N1‐X)] were synthesized and characterized in solution and solid‐state (X‐ray diffraction) revealing an arrangement similar to that of natural Watson–Crick base pairs. Subsequently, 1Pd‐DNA hybrids were prepared, characterized, and their structures studied by small‐angle X‐ray scattering (SAXS) and ab‐initio calculations. The results indicate that the 1Pd‐DNA structures resemble that of double‐stranded DNA, with one strand being replaced by a supramolecular stack of continuous PdII complexes. [ABSTRACT FROM AUTHOR]

Covalency is often considered to be an influential factor in driving An3+ vs. Ln3+ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An3+/Ln3+ covalency differences prevail and manifest as the f‐block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh2)2}3] (1‐Am, E=Se; 2‐Am, E=O) are compared to isoradial [Nd{N(E=PPh2)2}3] (1‐Nd, 2‐Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV‐vis‐NIR spectroscopy and single‐crystal X‐ray structures, we observe differences in f orbital involvement between Am–Se and Nd–Se bonds, which are not present in O‐donor congeners. [ABSTRACT FROM AUTHOR]

Phosphorene—the monolayered material of the element allotrope black phosphorus (Pblack)—and SnIP are 2D and 1D semiconductors with intriguing physical properties. Pblack and SnIP have in common that they can be synthesized via short way transport or mineralization using tin, tin(IV) iodide and amorphous red phosphorus. This top‐down approach is the most important access route to phosphorene. The two preparation routes are closely connected and differ mainly in reaction temperature and molar ratios of starting materials. Many speculative intermediates or activator side phases have been postulated especially for top‐down Pblack/phosphorene synthesis, such as Hittorf's phosphorus or Sn24P19.3I8 clathrate. The importance of phosphorus‐based 2D and 1D materials for energy conversion, storage, and catalysis inspired us to elucidate the formation mechanisms of these two compounds. Herein, we report on the reaction mechanisms of Pblack/phosphorene and SnIP from P4 and SnI2 via direct gas phase formation. [ABSTRACT FROM AUTHOR]

Examined here are the structures of complexes of benzophenone microsolvated with up to three water molecules by using broadband rotational spectroscopy and the cold conditions of a molecular jet. The analysis shows that the water molecules dock sideways on benzophenone for the water monomer and dimer moieties, and they move above one of the aromatic rings when the water cluster grows to the trimer. The rotational spectra shows that the water trimer moiety in the complex adopts an open‐loop arrangement. Ab initio calculations face a dilemma of identifying the global minimum between the open loop and the closed loop, which is only solved when zero‐point vibrational energy correction is applied. An OH⋅⋅⋅π bond and a Bürgi‐Dunitz interaction between benzophenone and the water trimer are present in the cluster. This work shows the subtle balance between water–water and water–solute interactions when the solute molecule offers several different anchor sites for water molecules. [ABSTRACT FROM AUTHOR]

The coherence time of the 17‐electron, mixed sandwich complex [CpTi(cot)], (η8‐cyclooctatetraene)(η5‐cyclopentadienyl)titanium, reaches 34 μs at 4.5 K in a frozen deuterated toluene solution. This is a remarkable coherence time for a highly protonated molecule. The intramolecular distances between the Ti and H atoms provide a good compromise between instantaneous and spin diffusion sources of decoherence. Ab initio calculations at the molecular and crystal packing levels reveal that the characteristic low‐energy ring rotations of the sandwich framework do not yield a too detrimental spin‐lattice relaxation because of their small spin–phonon coupling. The volatility of [CpTi(cot)] and the accessibility of the semi‐occupied, non‐bonding dz2 orbital make this neutral compound an ideal candidate for single‐qubit addressing on surface and quantum sensing in combination with scanning probe microscopy. [ABSTRACT FROM AUTHOR]

The fluoronitrenoid metal complexes FNCoF2 and FNRhF2 as well as the first ternary RhVI and IrVI complexes NIrF3 and NRhF3 are described. They were obtained by the reaction of excited Group‐9 metal atoms with NF3 and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed 14/15N isotope shifts and quantum‐chemical predictions, all four stretching fundamentals of the novel complexes were safely assigned. The F−N stretching frequencies of the fluoronitrenoid complexes FNCoF2 (1056.8 cm−1) and FNRhF2 (872.6 cm−1) are very different and their N−M bonds vary greatly. In FNCoF2, the FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character, while the N−Rh bond in FNRhF2 is a strong double bond with comparatively strong σ‐ and π‐bonds. The anticipated rearrangement of FNCoF2 to the nitrido CoVI complex is predicted to be endothermic and was not observed. [ABSTRACT FROM AUTHOR]

The fluoronitrenoid metal complexes FNCoF2 and FNRhF2 as well as the first ternary RhVI and IrVI complexes NIrF3 and NRhF3 are described. They were obtained by the reaction of excited Group‐9 metal atoms with NF3 and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed 14/15N isotope shifts and quantum‐chemical predictions, all four stretching fundamentals of the novel complexes were safely assigned. The F−N stretching frequencies of the fluoronitrenoid complexes FNCoF2 (1056.8 cm−1) and FNRhF2 (872.6 cm−1) are very different and their N−M bonds vary greatly. In FNCoF2, the FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character, while the N−Rh bond in FNRhF2 is a strong double bond with comparatively strong σ‐ and π‐bonds. The anticipated rearrangement of FNCoF2 to the nitrido CoVI complex is predicted to be endothermic and was not observed. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) has become a promising approach for the industrial production of graphene films with appealing controllability and uniformity. However, in the conventional hot‐wall CVD system, CVD‐derived graphene films suffer from surface contamination originating from the gas‐phase reaction during the high‐temperature growth. Shown here is that the cold‐wall CVD system is capable of suppressing the gas‐phase reaction, and achieves the superclean growth of graphene films in a controllable manner. The as‐received superclean graphene film, exhibiting improved optical and electrical properties, was proven to be an ideal candidate material used as transparent electrodes and substrate for epitaxial growth. This study provides a new promising choice for industrial production of high‐quality graphene films, and the finding about the engineering of the gas‐phase reaction, which is usually overlooked, will be instructive for future research on CVD growth of graphene. [ABSTRACT FROM AUTHOR]

We investigate a family of dinuclear dysprosium metallocene single‐molecule magnets (SMMs) bridged by methyl and halogen groups [Cp′2Dy(μ‐X)]2 (Cp′=cyclopentadienyltrimethylsilane anion; 1: X=CH3−; 2: X=Cl−; 3: X=Br−; 4: X=I−). For the first time, the magnetic easy axes of dysprosium metallocene SMMs are experimentally determined, confirming that the orientation of them are perpendicular to the equatorial plane which is made up of dysprosium and bridging atoms. The orientation of the magnetic easy axis for 1 deviates from the normal direction (by 10.3°) due to the stronger equatorial interactions between DyIII and methyl groups. Moreover, its magnetic axes show a temperature‐dependent shifting, which is caused by the competition between exchange interactions and Zeeman interactions. Studies of fluorescence and specific heat as well as ab initio calculations reveal the significant influences of the bridging ligands on their low‐lying exchange‐based energy levels and, consequently, low‐temperature magnetic properties. [ABSTRACT FROM AUTHOR]

Adenosine radicals tagged with a fixed‐charge group were generated in the gas phase and structurally characterized by tandem mass spectrometry, deuterium labeling, and UV/Vis action spectroscopy. Experimental results in combination with Born–Oppenheimer molecular dynamics, ab initio, and excited‐state calculations led to unambiguous assignment of adenosine radicals as N‐7 hydrogen atom adducts. The charge‐tagged radicals were found to be electronically equivalent to natural DNA nucleoside radicals. [ABSTRACT FROM AUTHOR]

A sample‐type protein monolayer, that can be a stepping stone to practical devices, can behave as an electrically driven switch. This feat is achieved using a redox protein, cytochrome C (CytC), with its heme shielded from direct contact with the solid‐state electrodes. Ab initio DFT calculations, carried out on the CytC–Au structure, show that the coupling of the heme, the origin of the protein frontier orbitals, to the electrodes is sufficiently weak to prevent Fermi level pinning. Thus, external bias can bring these orbitals in and out of resonance with the electrode. Using a cytochrome C mutant for direct S−Au bonding, approximately 80 % of the Au–CytC–Au junctions show at greater than 0.5 V bias a clear conductance peak, consistent with resonant tunneling. The on–off change persists up to room temperature, demonstrating reversible, bias‐controlled switching of a protein ensemble, which, with its built‐in redundancy, provides a realistic path to protein‐based bioelectronics. [ABSTRACT FROM AUTHOR]

Terminal oxo complexes of late transition metals are frequently proposed reactive intermediates. However, they are scarcely known beyond Group 8. Using mass spectrometry, we prepared and characterized two such complexes: [(N4Py)CoIII(O)]+ (1) and [(N4Py)CoIV(O)]2+ (2). Infrared photodissociation spectroscopy revealed that the Co−O bond in 1 is rather strong, in accordance with its lack of chemical reactivity. On the contrary, 2 has a very weak Co−O bond characterized by a stretching frequency of ≤659 cm−1. Accordingly, 2 can abstract hydrogen atoms from non‐activated secondary alkanes. Previously, this reactivity has only been observed in the gas phase for small, coordinatively unsaturated metal complexes. Multireference ab‐initio calculations suggest that 2, formally a cobalt(IV)‐oxo complex, is best described as cobalt(III)‐oxyl. Our results provide important data on changes to metal‐oxo bonding behind the oxo wall and show that cobalt‐oxo complexes are promising targets for developing highly active C−H oxidation catalysts. [ABSTRACT FROM AUTHOR]

Frontispiece: Dynamic Activation of Ga Sites by Pt Dopant in Low-Temperature Liquid-Metal Catalysts In their Communication (e202219009), Nicola Gaston and co-workers employ molecular dynamics simulations to examine GaPt catalysts in isolation and interacting with adsorbates. Keywords: Ab Initio Calculations; Gallium; Nanocatalysis; Platinum; Structure-Activity Relationships EN Ab Initio Calculations Gallium Nanocatalysis Platinum Structure-Activity Relationships 1 1 1 04/26/23 20230502 NES 230502 B Nanocatalysis b . [Extracted from the article]

The asymmetric catalysis of the intramolecular enone [2+2] photocycloaddition has been subject of extensive experimental studies, however theoretical insight to its regulatory mechanism is still sparse. Accurate quantum chemical calculations at the CASPT2//CASSCF level of theory associated with energy-consistent relativistic pseudopotentials provide a basis for the first regulation theory that the enantioselective reaction is predominantly controlled by the presence of relativistic effects, that is, spin-orbit coupling resulting from heavy atoms in the chiral Lewis acid catalyst. [ABSTRACT FROM AUTHOR]

Tuning charge transport at the single-molecule level plays a crucial role in the construction of molecular electronic devices. Introduced herein is a promising and operationally simple approach to tune two distinct charge-transport pathways through a cruciform molecule. Upon in situ cleavage of triisopropylsilyl groups, complete conversion from one junction type to another is achieved with a conductance increase by more than one order of magnitude, and it is consistent with predictions from ab initio transport calculations. Although molecules are well known to conduct through different orbitals (either HOMO or LUMO), the present study represents the first experimental realization of switching between HOMO- and LUMO-dominated transport within the same molecule. [ABSTRACT FROM AUTHOR]

The 'curly arrow' of Robinson and Ingold is the primary tool for describing and rationalizing reaction mechanisms. Despite this approach's ubiquity and stellar success, its physical basis has never been clarified and a direct connection to quantum chemistry has never been found. Here we report that the bond rearrangements expressed by curly arrows can be directly observed in ab initio computations, as transformations of intrinsic bond orbitals (IBOs) along the reaction coordinate. Our results clarify that curly arrows are rooted in physical reality-a notion which has been challenged before-and show how quantum chemistry can directly establish reaction mechanisms in intuitive terms and unprecedented detail. [ABSTRACT FROM AUTHOR]

The influence of nuclear spin on the magnetic hysteresis of a single-molecule is evidenced. Isotopically enriched DyIII complexes are synthesized and an isotopic dependence of their magnetic relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single-molecule magnets (SMMs), and provides an important step for their integration into molecule-based devices. [ABSTRACT FROM AUTHOR]

Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high-level electronic structure theory, we directly probe and identify higher electronically excited singlet states of the isolated para- and meta-chromophore anions of GFP. These molecular resonances are found to serve as a doorway for very efficient electron detachment in the gas phase. Inside the protein, this band is found to be resonant with the quasicontinuum of a solvated electron, thus enhancing electron transfer from the GFP to the solvent. This suggests a photophysical pathway for photoconversion of the protein, where GFP resonant photooxidation in solution triggers radical redox reactions inside these proteins. [ABSTRACT FROM AUTHOR]

Outside the cage: A change in the redox properties of a triazole fused to a carborane anion through methylation to form a zwitterion enabled facile chemical reduction of the compound to an isolable triazole radical anion (see structure: C gray, H white, N blue, B brown, Cl green). The radical anion is stabilized by kinetic protection by the chlorinated carborane and the delocalization of spin density throughout the exo‐cluster π system. [ABSTRACT FROM AUTHOR]

Keywords: ab initio calculations; IRMPD spectroscopy; non-innocent ligands; radical ions; reactive intermediates EN ab initio calculations IRMPD spectroscopy non-innocent ligands radical ions reactive intermediates 1 1 1 04/27/22 20220502 NES 220502 In the present Communication the article by Bau and co-workers[1] on the synthesis and characterization of the homoleptic [Pt(C SB 6 sb Cl SB 5 sb ) SB 4 sb ] SP - sp anion was incorrectly cited in support of the statement "Platinum(III) complexes are indeed elusive species, which are seldom observed as mononuclear complexes and the radical is often found to be localized on the ligands rather than on the metal center". Ab initio calculations, radical ions, reactive intermediates, IRMPD spectroscopy, non-innocent ligands. [Extracted from the article]

Keywords: ab initio calculations; lithium-ion batteries; oxygen redox; peroxo formation; X-ray spectroscopy EN ab initio calculations lithium-ion batteries oxygen redox peroxo formation X-ray spectroscopy 9730 9730 1 04/26/21 20210426 NES 210426 B Peroxo formation b is the crucial step in oxygen redox. Ab initio calculations, lithium-ion batteries, oxygen redox, peroxo formation, X-ray spectroscopy The reversible oxygen transformation following cationic redox is promising for high-energy, high-safety lithium-ion batteries. [Extracted from the article]

Actinides, americium, covalency, spectroscopy, structure Keywords: actinides; americium; covalency; spectroscopy; structure EN actinides americium covalency spectroscopy structure 9728 9728 1 04/15/21 20210419 NES 210419 B Differential covalency b in trivalent actinide versus lanthanide bonding with soft donors can aid separations. Hard-O Donor Bonding in Trivalent Americium/Neodymium Molecules (Angew. [Extracted from the article]

Keywords: ab initio calculations; fluxionality; isomerization; Jahn-Teller effect; photoelectron spectroscopy EN ab initio calculations fluxionality isomerization Jahn-Teller effect photoelectron spectroscopy 8009 8009 1 04/01/21 20210406 NES 210406 In this Review article, the captions of Figures 14 and 16 should be amended to include references to primary data used earlier. Corrigendum: Jahn-Teller Effects in Molecular Cations Studied by Photoelectron Spectroscopy and Group Theory Ab initio calculations, fluxionality, isomerization, Jahn-Teller effect, photoelectron spectroscopy. [Extracted from the article]