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Quantum information theory provides a powerful toolbox of descriptors that characterize many‐electron systems based on quantum information patterns between open quantum systems. Despite the wealth of insights gained in the condensed matter community, the use of these descriptors to study interactions between atoms in a molecule remains limited. In this study, we develop a quantum information framework for molecules that characterizes the quantum information patterns between quantum atoms as defined in the Quantum Theory of Atoms in Molecules. We show that quantum information analyses capture key properties of quantum atoms and how they interact with their molecular environment. Additionally, we show that the presence of bond critical points can remain invariant despite large changes in the quantum information patterns between the quantum atoms. Our findings indicate that quantum information theory can shed a new light on molecular electronic structure. [ABSTRACT FROM AUTHOR]

The role of the coinage metal in monomeric hydride complexes for the reduction of carbon dioxide to formate has been computationally addressed in this work. The common reaction mechanism, i. e. a concerted M−H (M=Cu, Ag, Au) bond attack to the CO2 carbon atom with one oxygen atom coordinating to the metal center, has been analyzed, revealing a kinetically less favorable reactivity for the gold‐hydride complex. A thorough computational investigation discloses that, while all complexes feature covalent electron‐sharing M−H bonds, copper‐ and silver‐hydride complexes display a relevant M(δ+)−H(δ−) bond polarization, which enables an enhanced basicity of the hydride and, thereby, a more kinetically favorable CO2 reduction process. This study provides useful guidelines for the design of monomeric metal hydride complexes as promising candidates for the CO2 reduction. [ABSTRACT FROM AUTHOR]

Bonding interactions and spin-orbit coupling in the topological insulator SrAg4 Sb2 are investigated using DFT with orbital projection analysis. Ag-Ag delta bonding is a key ingredient in the topological insulating state because the 4dxy+4dx2-y2${4d_{xy} + 4d_{x^2 - y^2 } }$ delta antibonding band forms a band inversion with the 5 s sigma bonding band. Spin-orbit coupling is required to lift d orbital degeneracies and lower the antibonding band enough to create the band inversion. These bonding effects are enabled by a longer-than-covalent Ag-Ag distance in the crystal lattice, which might be a structural characteristic of other transition metal based topological insulators. A simplified model of the topological bands is constructed to capture the essence of the topological insulating state in a way that may be engineered in other materials.

This study established the connection between structure and dielectric responses by synergistically evaluating the chemical bond characteristics and lattice vibrational spectroscopies of trirutile ATa 2 O 6 (A = Mg, Ni) microwave ceramics. The MgTa 2 O 6 ceramic exhibits a uniform grain size distribution and a dense microstructure, with dielectric characteristics at microwave range of a ε r value of 27.27, a high Q × f value of 109,203 GHz (8.73 GHz), and a τ f of approximately 53.38 ppm/°C when sintered at 1300 °C, while the NiTa 2 O 6 ceramic presents a smaller average grain size and minor micropores, with dielectric characteristics at microwave range of ε r = 24.58, Q × f = 27,610 GHz (9.25 GHz), and τ f = 33.94 ppm/°C, sintered at 1250 °C. The structural refinement and atomic arrangements confirm a trirutile structure along the [001], [100], and [3 3 ‾ 1 ‾ ] zone axes. Ta–O bonds are found to contribute the most to the ionic character of a bond, bond susceptibility, lattice stability, thermal expansion behaviors, and strength of bonding ability, indicating their significant influence on dielectric polarization, lattice stability, and temperature coefficient of resonant frequency. Raman scattering spectra analysis reveals that the A 1g mode near 700 cm−1 mainly controls the Raman vibrational behaviors. The theoretical dielectric properties calculated from the infrared spectrum and dielectric properties analysis consistent with the measured dielectric performances, suggesting that the dielectric characteristics at the microwave range are mainly determined by the oscillatory absorption of structural phonons, with the first two modes at 210.48 cm−1 and 232.87 cm−1 contributing 72.02% to the ε r value and 90.45% to the tan δ value, respectively. [ABSTRACT FROM AUTHOR]

Bonding interactions and spin‐orbit coupling in the topological insulator SrAg4Sb2 are investigated using DFT with orbital projection analysis. Ag−Ag delta bonding is a key ingredient in the topological insulating state because the 4dxy+4dx2-y2 ${4d_{xy} + 4d_{x^2 - y^2 } }$ delta antibonding band forms a band inversion with the 5 s sigma bonding band. Spin‐orbit coupling is required to lift d orbital degeneracies and lower the antibonding band enough to create the band inversion. These bonding effects are enabled by a longer‐than‐covalent Ag−Ag distance in the crystal lattice, which might be a structural characteristic of other transition metal based topological insulators. A simplified model of the topological bands is constructed to capture the essence of the topological insulating state in a way that may be engineered in other materials. [ABSTRACT FROM AUTHOR]

We have quantum chemically investigated the boron‐boron bonds in B2, diborynes B2L2, and diborenes B2H2L2 (L=none, OH2, NH3) using dispersion‐corrected relativistic density functional theory at ZORA‐BLYP‐D3(BJ)/TZ2P. B2 has effectively a single B−B bond provided by two half π bonds, whereas B2H2 has effectively a double B=B bond provided by two half π bonds and one σ 2p–2p bond. This different electronic structure causes B2 and B2H2 to react differently to the addition of ligands. Thus, in B2L2, electron‐donating ligands shorten and strengthen the boron‐boron bond whereas, in B2H2L2, they lengthen and weaken the boron‐boron bond. The aforementioned variations in boron‐boron bond length and strength become more pronounced as the Lewis basicity of the ligands L increases. [ABSTRACT FROM AUTHOR]

The synthesis and first structural characterization of the [K(18‐crown‐6)] bismolyl Bitet (C4Me4Bi) contact ion pair (1) is presented. Notably, according to Natural Resonance Theory calculations, the Bitet anion of 1 features two types of leading mesomeric structures with localized anionic charge and two lone pairs of electrons at the BiI center, as well as delocalized anionic charge in the π‐conjugated C4Bi ring. The lone pairs at Bi enable a unique bridging coordination mode of the bismolyl ligand, as shown for the first rare earth metal bismolyl complex (Cptet2Y)2(μ‐η1‐Bitet)2 (2). The latter results from the salt metathesis reaction of KBitet with Cptet2Y(BPh4) (Cptet=C5Me4H). The Y‐Bi bonding interaction in 2 of 16.6 % covalency at yttrium is remarkably large. [ABSTRACT FROM AUTHOR]

Understanding the bonding of gold(I) species has been central to the development of gold(I) catalysis. Herein, we present the synthesis and characterization of the first gold(I)-cyclobutadiene complex, accompanied with bonding analysis by state-of-the-art energy decomposition analysis methods. Analysis of possible coordination modes for the new species not only confirms established characteristics of gold(I) bonding, but also suggests that Pauli repulsion is a key yet hitherto overlooked element. Additionally, we obtain a new perspective on gold(I)-bonding by comparison of the gold(I)-cyclobutadiene to congeners stabilized by p-, d-, and f-block metals. Consequently, we refine the gold(I) bonding model, with a delicate interplay of Pauli repulsion and charge transfer as the key driving force for various coordination motifs. Pauli repulsion is similarly determined as a significant interaction in AuI -alkyne species, corroborating this revised understanding of AuI bonding.

We considered it timely to test the applicability of transferable multipole pseudo-atoms for restoring inner-crystal electronic force density fields. The procedure was carried out on the crystal of 1,3-bis(2-hydroxyethyl)-6-methyluracil, and some derived properties of the scalar potential and vector force fields were compared with those obtained from the experimental multipole model and from the aspherical pseudo-atom model with parameters fitted to the calculated structure factors. The procedure was shown to accurately replicate the general vector-field behavior, the peculiarities of the quantum potentials and the characteristics of the force-field pseudoatoms, such as charge, shape and volume, as well as to reproduce the relative arrangement of atomic and pseudoatomic zero-flux surfaces along internuclear regions. It was found that, in addition to the quantum-topological atoms, the force-field pseudoatoms are spatially reproduced within a single structural fragment and similar environment. In addition, the classical and nonclassical hydrogen bonds in the uracil derivative crystal, as well as the H...O, N...O and N...C interactions in the free π-stacked dimer of the uracil derivative molecules, were studied using the potential and force fields within the concepts of interatomic charge transfer and electron lone pair donation–acceptance. Remarkably, the nitrogen atoms in the N...O and N...C interactions behave rather like a Lewis base and an electron contributor. At the same time, the hydrogen atom in the H...O interaction, being a Lewis acid, also participates in the interatomic electron transfer by acting as a contributor. Thus, it has been argued that, when describing polar interatomic interactions within orbital-free considerations, it makes more physical sense to identify electronegative (electron occupier) and electropositive (electron contributor) atoms or subatomic fragments rather than nucleophilic and electrophilic sites.

The Zintl–Klemm idea is a remarkable formalism that can guide us through the crystal structure–electronic structure relationships of solids showing a particular correlation between charge transfers, (8–N) rule and the corresponding structural fragments. Accordingly, this approach has been applied to interpret the relationships between the crystal and electronic structures for numerous intermetallics; yet, are all of these applications of the Zintl–Klemm idea indeed helpful? To answer this question, quantumchemical means were used to explore the electronic structures of three prototypical intermetallics, i.e. LiY2Si2, Sc2Si2Al, and Y2Pd2In. These compounds crystallize with the Mo2FeB2 type of structure whose structure model may be derived from that of the widely encountered U3Si2‐type. The explorations of the electronic structures included examinations of the Mulliken charges, the projected crystal orbital Hamilton populations (pCOHP), the recently introduced crystal orbital bond indices (COBI) and the respective integrated pCOHP as well as COBI values (IpCOHP and ICOBI). The outcome of these investigations indicates that widely diverse types of bonding are evident for the inspected intermetallics so that the predictive power of the Zintl–Klemm idea is limited. [ABSTRACT FROM AUTHOR]

We provide a complete classification of paradoxical closed-loop n-linkages, where n ≥ 6 , of mobility n - 4 or higher, containing revolute, prismatic or helical joints. We also explicitly write down strong necessary conditions for nR-linkages of mobility n - 5 . Our main new tool is a geometric relation between a linkage L and another linkage L ′ resulting from adding equations to the configuration space of L. We then lift known classification results for L ′ to L using this relation. [ABSTRACT FROM AUTHOR]

Quantum chemical methods were employed to analyze the nature and the origin of the directionality of pnictogen (PnB), chalcogen (ChB), and halogen bonds (XB) in archetypal FmZ⋅⋅⋅F− complexes (Z=Pn, Ch, X), using relativistic density functional theory (DFT) at ZORA‐M06/QZ4P. Quantitative Kohn‐Sham MO and energy decomposition analyses (EDA) show that all these intermolecular interactions have in common that covalence, that is, HOMO−LUMO interactions, provide a crucial contribution to the bond energy, besides electrostatic attraction. Strikingly, all these bonds are directional (i.e. F−Z⋅⋅⋅F− is approximately linear) despite, and not because of, the electrostatic interactions which, in fact, favor bending. This constitutes a breakdown of the σ‐hole model. It was shown how the σ‐hole model fails by neglecting both, the essential physics behind the electrostatic interaction and that behind the directionality of electron‐rich intermolecular interactions. Our findings are general and extend to the neutral, weaker ClI⋅⋅⋅NH3, HClTe⋅⋅⋅NH3, and H2ClSb⋅⋅⋅NH3 complexes. [ABSTRACT FROM AUTHOR]

Abstract We have quantum chemically analyzed the origin of the captodative effect in the dimerization of para‐substituted phenyl dicyanomethyl radicals RPh(CN)2C⋅ in the gas phase and in solution. Captodative radicals are characterized by the presence of both, electron‐donating and electron‐withdrawing groups, and a weakening of the associated C−C bond in the dimer of these radicals. Our quantitative bonding analyses reveal that the captodative weakening of the C−C bond is the consequence of a special feature in the RPh(CN)2C⋅ electronic structure which we designate “lone‐pair shielded radical”. Solvation effects weaken the C−C bond as the radicals have a more prominent internal charge separation than the dimer and are, therefore, stabilized more than the intact dimer. Interestingly, we find that differences in solvent effects as a function of the para‐substituent in the most prominent case arise from variations in the charge distribution in the dimer, not from that in the separate radicals which experience very similar solvation in those instances.

Schnöckel's [(AlCp*)4] and Jutzi's [SiCp*][B(C6F5)4] (Cp*=C5Me5) are landmarks in modern main‐group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3][WCA] ([WCA]−=[Al(ORF)4]− and [F{Al(ORF)3}2]−; RF=C(CF3)3). The tetrahedral [SiAl3]+ core not only represents a rare example of a low‐valent silicon‐doped aluminium‐cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low‐valent Si−Al clusters in general. For example, an elusive binuclear [Si2(AlCp*)5]2+ with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2(AlCp*)5]2+ dication were also obtained and represent the first mixed Al−Ge cluster. [ABSTRACT FROM AUTHOR]

Elucidating how the halogen‐bonding ability and strength are controlled by the substituent effect and how this control depends on halogen atom will be essential for finely‐tuned design of functionally important molecules. Here, this problem is tackled by analyzing the electron density differences/changes for variously substituted halobenzenes. It is shown that the anisotropy of the electron distribution around the halogen atom, which is an important factor for halogen‐bonding ability, is not much affected by the substituent effect and rather simply depends on the halogen atom, while the partial charge on the halogen atom, which is related to the bond dipole of the C−X bond, is significantly modulated by the substituent effect and gives rise to enhancement of the electrostatic potential on the line extended from the C−X bond. The properties related to the polarization effect are also discussed. [ABSTRACT FROM AUTHOR]

The development of ligands capable of effectively stabilizing highly reactive main‐group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity‐enforced group 13–15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8‐naphthyridine (napy) core. We show that the redox‐active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element‐element interaction modes, the latter ranging from isolated, element‐centered lone pairs (e.g., E = Si, Ge) to cases where through‐space π bonds (E = Pb), element‐element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI‐E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy‐based ligands in main‐group chemistry. [ABSTRACT FROM AUTHOR]

Reported here is an ab initio modelling of C−C bonding in halocarbon molecules, with alkali‐metal atoms attached. The studied systems feature metal‐halide counterion pairs appearing along the way. Their electric field leads to a mutual attraction, as well as influences the process directly. Such a combination favours bonding of reactants over significantly reduced potential energy barriers. The process involves uncommon species including a counterintuitive isomer of a metal‐halocarbon system bound via "collective" ionic bonds, an intermediate charge‐transfer complex exhibiting an unusual hyper‐coordinated carbon, and possible another (also uncommon) intermediate insertion complex with a molecule trapped between counterions. The overall reaction involves an "umbrella"‐type inversion of bonds and recombination of framing metal‐halide ion‐pair around insert. The process could be tracked via IR spectra at all stages, from reactants through intermediates to products. This could enable experimental detection of relevant species formation, their differentiation, and monitoring overall system evolution. [ABSTRACT FROM AUTHOR]

Spectroscopic and computational examination of a homologous series of rhodium(I) pybox carbonyl complexes has revealed a correlation between the conformation of the flanking aryl‐substituted oxazoline donors and the carbonyl stretching frequency. This relationship is also observed experimentally for octahedral rhodium(III) and ruthenium(II) variants and cannot be explained through the classical, Dewar–Chatt–Duncanson, interpretation of metal‐carbonyl bonding. Instead, these findings are reconciled by local changes in the magnitude of the electric field that is projected along the metal‐carbonyl vector: the internal Stark effect. [ABSTRACT FROM AUTHOR]

Schnöckel's [(AlCp*)4] and Jutzi's [SiCp*][B(C6F5)4] (Cp*=C5Me5) are landmarks in modern main‐group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3][WCA] ([WCA]−=[Al(ORF)4]− and [F{Al(ORF)3}2]−; RF=C(CF3)3). The tetrahedral [SiAl3]+ core not only represents a rare example of a low‐valent silicon‐doped aluminium‐cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low‐valent Si−Al clusters in general. For example, an elusive binuclear [Si2(AlCp*)5]2+ with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2(AlCp*)5]2+ dication were also obtained and represent the first mixed Al−Ge cluster. [ABSTRACT FROM AUTHOR]

Surface atoms and dangling bonds on the surface affect the thermodynamic properties. A thermodynamical model, based on cohesive energy is presented to discuss the melting properties of materials at nanoscale. The model is used to realize the effect of size and shape on melting temperature Tmn, melting entropy Smn and enthalpy Hmn of Ni, Sn, Al and Cu metallic nanoparticles. The variation in Tmn, Smn and Hmn are examined for nanowire, film, spherical, regular tetrahedral, hexahedral and octahedral shaped nanoparticles. It is reported that Tmn, Smn and Hmn decrease with decreasing the size of the nanoparticles and smaller the particle size, greater are the size and shape effects and when size is less than 10 nm, it has been predicted that on decreasing size, Tmn, Smn and Hmn reduce appreciably. Also, at the same size, more the shape of nanoparticles departs from that of the sphere, smaller is the Smn and Hmn of nanoparticles and its changes are less for nanowire shape and more for regular tetrahedral shape. Our theoretical results are compared with the available experimental or simulation data. Results predicted by our model are in good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Intricate behaviour of one‐electron potentials from the Euler equation for electron density and corresponding gradient force fields in crystals was studied. Channels of locally enhanced kinetic potential and corresponding saddle Lagrange points were found between chemically bonded atoms. Superposition of electrostatic ϕesr and kinetic ϕkr potentials and electron density ρr allowed partitioning any molecules and crystals into atomic ρ ‐ and potential‐based ϕ ‐basins; ϕk ‐basins explicitly account for the electron exchange effect, which is missed for ϕes ‐ones. Phenomena of interatomic charge transfer and related electron exchange were explained in terms of space gaps between zero‐flux surfaces of ρ ‐ and ϕ ‐basins. The gap between ϕes ‐ and ρ ‐basins represents the charge transfer, while the gap between ϕk ‐ and ρ ‐basins is a real‐space manifestation of sharing the transferred electrons caused by the static exchange and kinetic effects as a response against the electron transfer. The regularity describing relative positions of ρ ‐, ϕes ‐, and ϕk ‐ basin boundaries between interacting atoms was proposed. The position of ϕk ‐boundary between ϕes ‐ and ρ ‐ones within an electron occupier atom determines the extent of transferred electron sharing. The stronger an H⋅⋅⋅O hydrogen bond is, the deeper hydrogen atom's ϕk ‐basin penetrates oxygen atom's ρ ‐basin, while for covalent bonds a ϕk ‐boundary closely approaches a ϕes ‐one indicating almost complete sharing of the transferred electrons. In the case of ionic bonds, the same region corresponds to electron pairing within the ρ ‐basin of an electron occupier atom. [ABSTRACT FROM AUTHOR]

Relativistic effects are known to alter the chemical bonds and spectroscopic properties of heavy‐element compounds. In this work, we introduce the concept of spin–orbit (SO) electronegativity of a heavy atom, as reflected by an SO‐induced change in the interatomic distance between the heavy atom (HA) and a neighboring light atom (LA). We provide a transparent interpretation of these SO effects by using the concept of spin–orbit electron deformation density (SO‐EDD). Spin–orbit coupling at the HA induces rearrangement of the electron density for the scalar‐relativistically optimized geometry that, in turn, exerts a new force on the LA. The resulting expansion or contraction of the HA−LA bond depends on the nature and electron configuration of the HA. In addition, we quantify the change in atomic electronegativity induced by SO coupling for a series of hydrides, thereby complementing the SO‐EDD picture. The trends in the SO‐induced electronegativity and the HA−LA bond length across the periodic table of elements are demonstrated and interpreted, and also linked, intuitively, with the SO‐induced NMR shielding at the LA. [ABSTRACT FROM AUTHOR]

Beryllium, an s‐block element, forms an aromatic network of delocalized Be–Be π bonds in alloys ZrBe2 and HfBe2. This gives rise to stacked [Be2]4− layers with tetravalent cations in between. The [Be2]4− sublattice is isoelectronic and isostructural to graphite, as well as the [B]−2 sublattice in MgB2, and it bears identical manifestations of π bonding in its electronic band structure. These come in the form of degeneracies at K and H in the Brillouin zone, separated in energy as the result of interlayer orbital interactions. Zr and Hf use their valence d orbitals to form bonds with the layers, leading to nearly identical band structures. Like MgB2, ZrBe2 and HfBe2 are computed to be phonon‐mediated superconductors at ambient pressures, with respective critical temperatures of 11.4 K and 8.8 K. The coupling strength between phonons and free electrons is very similar, so that the difference in critical temperatures is controlled by the mass of constituent interlayer ions. [ABSTRACT FROM AUTHOR]

Beryllium, an s‐block element, forms an aromatic network of delocalized Be–Be π bonds in alloys ZrBe2 and HfBe2. This gives rise to stacked [Be2]4− layers with tetravalent cations in between. The [Be2]4− sublattice is isoelectronic and isostructural to graphite, as well as the [B]−2 sublattice in MgB2, and it bears identical manifestations of π bonding in its electronic band structure. These come in the form of degeneracies at K and H in the Brillouin zone, separated in energy as the result of interlayer orbital interactions. Zr and Hf use their valence d orbitals to form bonds with the layers, leading to nearly identical band structures. Like MgB2, ZrBe2 and HfBe2 are computed to be phonon‐mediated superconductors at ambient pressures, with respective critical temperatures of 11.4 K and 8.8 K. The coupling strength between phonons and free electrons is very similar, so that the difference in critical temperatures is controlled by the mass of constituent interlayer ions. [ABSTRACT FROM AUTHOR]

The nature of the C−I⋅⋅⋅π halogen bonding and its mode of activation in organocatalysis have been quantitatively explored in detail by means of Density Functional Theory (DFT) calculations. To this end, the uncatalyzed homo‐[4+2]‐cycloaddition reaction involving 2‐alkenylindoles is compared to the analogous process mediated by iodine‐substituted azolium salts. It is found that the catalysts establish relatively strong C−I⋅⋅⋅π noncovalent interactions with the indole reactant, which are characterized by a high degree of covalency. This interaction results in a significant acceleration of the cycloaddition by lowering the activation barrier up to 6 kcal/mol with respect to the uncatalyzed reaction. The calculations predict that this barrier can be further reduced by increasing the electrophilicity of the catalyst. Our quantitative analyses reveal that the origin of the catalysis is found mainly in a significant reduction of the steric (Pauli) repulsion between the diene and dienophile, therefore confirming the generality of the recently introduced Pauli‐repulsion lowering concept. [ABSTRACT FROM AUTHOR]

The enhancement of the peptide bond order by a resonance in the lone pair of N and the π-bond of CO is analyzed. A decomposition of the bond order in terms of localized molecular orbitals is developed and applied to the peptide bond. A combination of two rotations of hybrid orbitals is proposed to improve the boundary treatment in the fragment molecular orbital method. The developed approach is applied to peptide bonds, and it is found crucial to retain the π orbital in the variational space of both fragments across the boundary. The interaction energies between conventional amino acid residues in Trp-cage (1L2Y) are discussed., (© 2024 Wiley-VCH GmbH.)

We have quantum chemically analyzed element−element bonds of archetypal HnX−YHn molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g. from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance. [ABSTRACT FROM AUTHOR]

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1JNC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1JNC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1JNC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å. [ABSTRACT FROM AUTHOR]

Disproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl3)4]. Spectroscopic analyses of the yellow‐whitish solid with IR‐, Raman‐, and NMR‐spectroscopy (29Si, 11B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1J(11B,29Si) and even 1J (10B, 29Si) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para‐protonated toluene cation and the weakly coordinating borate anion [B(SiCl3)4]−. Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar Si−Cl and Si−B bonds. Highly reactive compounds [E(SiCl3)n]− which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl3)4] represents a new member in this elusive compound family. [ABSTRACT FROM AUTHOR]

Disproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl3)4]. Spectroscopic analyses of the yellow‐whitish solid with IR‐, Raman‐, and NMR‐spectroscopy (29Si, 11B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1J(11B,29Si) and even 1J (10B, 29Si) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para‐protonated toluene cation and the weakly coordinating borate anion [B(SiCl3)4]−. Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar Si−Cl and Si−B bonds. Highly reactive compounds [E(SiCl3)n]− which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl3)4] represents a new member in this elusive compound family. [ABSTRACT FROM AUTHOR]

A detailed analysis of a complete set of the local potentials that appear in the Euler equation for electron density is carried out for noncovalent interactions in the crystal of a uracil derivative using experimental X‐ray charge density. The interplay between the quantum theory of atoms in molecules and crystals and the local potentials and corresponding inner‐crystal electronic forces of electrostatic and kinetic origin is explored. Partitioning of crystal space into atomic basins and atomic‐like potential basins led us to the definite description of interatomic interaction and charge transfer. Novel physically grounded bonding descriptors derived within the orbital‐free quantum crystallography provided the detailed examination of π‐stacking and intricate C=O⋅⋅⋅π interactions and nonclassical hydrogen bonds present in the crystal. The donor‐acceptor character of these interactions is revealed by analysis of Pauli and von Weizsäcker potentials together with well‐known functions, e. g., deformation electron density and electron localization function. In this way, our analysis throws light on aspects of these closed‐shell interactions hitherto hidden from the description. [ABSTRACT FROM AUTHOR]

Proximal noncovalent forces are commonplace in natural systems and understanding the consequences of their juxtaposition is critical. This paper experimentally quantifies for the first time a Hydrogen Bond‐Enhanced Halogen Bond (HBeXB) without the complexities of protein structure or preorganization. An HBeXB is a halogen bond that has been strengthened when the halogen donor simultaneously accepts a hydrogen bond. Our theoretical studies suggest that electron‐rich halogen bond donors are strengthened most by an adjacent hydrogen bond. Furthermore, stronger hydrogen bond donors enhance the halogen bond the most. X‐ray crystal structures of halide complexes (X−=Br−, I−) reveal that HBeXBs produce shorter halogen bonds than non‐hydrogen bond analogues. 19F NMR titrations with chloride highlight that the HBeXB analogue exhibits stronger binding. Together, these results form the foundation for future studies concerning hydrogen bonds and halogen bonds in close proximity. [ABSTRACT FROM AUTHOR]

We have quantum chemically studied the structure and nature of alkali‐ and coinage‐metal bonds (M‐bonds) versus that of hydrogen bonds between A−M and B− in archetypal [A−M⋅⋅⋅B]− model systems (A, B=F, Cl and M=H, Li, Na, Cu, Ag, Au), using relativistic density functional theory at ZORA‐BP86‐D3/TZ2P. We find that coinage‐metal bonds are stronger than alkali‐metal bonds which are stronger than the corresponding hydrogen bonds. Our main purpose is to understand how and why the structure, stability and nature of such bonds are affected if the monovalent central atom H of hydrogen bonds is replaced by an isoelectronic alkali‐ or coinage‐metal atom. To this end, we have analyzed the bonds between A−M and B− using the activation strain model, quantitative Kohn‐Sham molecular orbital (MO) theory, energy decomposition analysis (EDA), and Voronoi deformation density (VDD) analysis of the charge distribution. [ABSTRACT FROM AUTHOR]

The σ‐hole is an important concept which has been widely used lately to describe the halogen bond (XB) essentially as electrostatic in nature. However, this idea is not free of controversy. For the sake of this work, localised molecular orbital energy decomposition analysis (LMOEDA), interacting quantum atom (IQA) method and analysis of the electrostatic potential have been applied to O−Cl⋅⋅⋅B (B=CO, PH3, SH2, CS, NH3, OH−) complexes. The results show that in their equilibrium geometry the stabilizing effect that arises from the Pauli exclusion principle is larger in magnitude than the electrostatic interactions. Besides, it appears that an electronic exchange channel is established at a certain approach distance between the monomers. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations and NBO, ETS‐NOCV, QTAIM and ELF interpretative approaches have been carried out on C‐donor ligand‐stabilized dihydrido borenium cations. Numerous descriptors of the C−B π‐bond strength obtained from orbital localization, energy partitioning or topological methods as well as from structural and chemical parameters have been calculated for 39 C‐donor ligands including N‐heterocyclic carbenes and carbones. Comparison of the results allows the identification of relative and absolute descriptors of the π interaction. For both families of descriptors excellent correlations are obtained. This enables the establishment of a π‐donation capability scale and shows that the interpretative methods, despite their conceptual differences, describe the same chemical properties. These results also reveal noticeable shortcomings in these popular methods, and some precautions that need to be taken to interpret their results adequately. [ABSTRACT FROM AUTHOR]

The Periodic Table, and the unique chemical behavior of the first element in a column (group), were discovered simultaneously one and a half centuries ago. Half a century ago, this unique chemistry of the light homologs was correlated to the then available atomic orbital (AO) radii. The radially nodeless 1s, 2p, 3d, 4f valence AOs are particularly compact. The similarity of r(2s)≈r(2p) leads to pronounced sp‐hybrid bonding of the light p‐block elements, whereas the heavier p elements with n≥3 exhibit r(ns) ≪r(np) of approximately −20 to −30 %. Herein, a comprehensive physical explanation is presented in terms of kinetic radial and angular, as well as potential nuclear‐attraction and electron‐screening effects. For hydrogen‐like atoms and all inner shells of the heavy atoms, r(2s) ≫r(2p) by +20 to +30 %, whereas r(3s)≳r(3p)≳r(3d), since in Coulomb potentials radial motion is more radial orbital expanding than angular motion. However, the screening of nuclear attraction by inner core shells is more efficient for s than for p valence shells. The uniqueness of the 2p AO is explained by this differential shielding. Thereby, the present work paves the way for future physical explanations of the 3d, 4f, and 5g cases. [ABSTRACT FROM AUTHOR]

The concepts of nucleophilicity and protophilicity are fundamental and ubiquitous in chemistry. A case in point is bimolecular nucleophilic substitution (SN2) and base‐induced elimination (E2). A Lewis base acting as a strong nucleophile is needed for SN2 reactions, whereas a Lewis base acting as a strong protophile (i.e. base) is required for E2 reactions. A complicating factor is, however, the fact that a good nucleophile is often a strong protophile. Nevertheless, a sound, physical model that explains, in a transparent manner, when an electron‐rich Lewis base acts as a protophile or a nucleophile, which is not just phenomenological, is currently lacking in the literature. To address this fundamental question, the potential energy surfaces of the SN2 and E2 reactions of X−+C2H5Y model systems with X, Y = F, Cl, Br, I, and At, are explored by using relativistic density functional theory at ZORA‐OLYP/TZ2P. These explorations have yielded a consistent overview of reactivity trends over a wide range in reactivity and pathways. Activation strain analyses of these reactions reveal the factors that determine the shape of the potential energy surfaces and hence govern the propensity of the Lewis base to act as a nucleophile or protophile. The concepts of "characteristic distortivity" and "transition state acidity" of a reaction are introduced, which have the potential to enable chemists to better understand and design reactions for synthesis. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations of the alkaline‐earth oxides, imides and dihydrides of the alkaline‐earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca6H9[N(SiMe3)2]3(pmdta)3 (pmdta=N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n−1)d orbitals. The alkaline‐earth metals Be and Mg build covalent bonds like typical main‐group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline‐earth metals, but are also very important for understanding and designing experimental studies. [ABSTRACT FROM AUTHOR]

Weak binding of hydrogen atoms to the 2H‐MoS2 basal plane renders MoS2 inert as an electrocatalyst for the hydrogen evolution reaction. Transition‐metal doping can activate neighboring sulfur atoms in the MoS2 basal plane to bind hydrogen more strongly. Our theoretical studies show strong variation in the degree of activation by dopants across the 3d transition‐metal series. To understand the trends in activation, we propose a model based on the electronic promotion energy required to partially open the full valence shell of a local S atom and therefore enable it to bond with a H atom. In general, the promotion is achieved through an electron transfer from the S to neighboring metal‐atom sites. Furthermore, we demonstrate a specific, electronic‐structure‐based descriptor for the hydrogen‐binding strength: Δdp, the local interband energy separation between the lowest empty d‐states on the dopant metal atoms and occupied p‐states on S. This model can be used to provide guidelines for chalcogen activation in future catalyst design based on doped transition‐metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been performed to search for the possibility of dative bond formation between two old neighbors, boron and beryllium. The studied compounds have been found to have high bond dissociation energies. The thermodynamics of their formation is also very favorable. Different bonding as well as topological analyses confirm the presence of a dative bond between the two neighbors. Owing to the scarcity of B–Be bonded compounds, this study aims to extend the library of such compounds. [ABSTRACT FROM AUTHOR]

In this study, intrinsic dielectric properties of monoclinic A 0.5 Zr 0.5 NbO 4 ceramics (A = Mn, Zn, Mg, Co, Ni) with wolframite structure were investigated by chemical bond theory, infrared and terahertz spectroscopy. According to bond theory, Zr–O bonds and A-O bonds with larger bond susceptibility values provide majority contributions to relative permittivity; while Nb–O bonds dominate the structural stability and oxygen polyhedron distortion. Intrinsic dielectric properties calculated via far-infrared reflectivity spectroscopy are close to experimental properties, which indicates that most of dielectric contributions come from absorptions of structural phonon oscillation and infrared modes of dielectric response in A 0.5 Zr 0.5 NbO 4 ceramics vary with A-site ions. Furthermore, intrinsic properties estimated by terahertz time domain spectra also testify the effectiveness of theoretical dielectric properties. [ABSTRACT FROM AUTHOR]

Charge‐shift bonds (CSBs) constitute a new class of bonds different than covalent/polar‐covalent and ionic bonds. Bonding in CSBs does not arise from either the covalent or the ionic structures of the bond, but rather from the resonance interaction between the structures. This Essay describes the reasons why the CSB family was overlooked by valence‐bond pioneers and then demonstrates that the unique status of CSBs is not theory‐dependent. Thus, valence bond (VB), molecular orbital (MO), and energy decomposition analysis (EDA), as well as a variety of electron density theories all show the distinction of CSBs vis‐à‐vis covalent and ionic bonds. Furthermore, the covalent–ionic resonance energy can be quantified from experiment, and hence has the same essential status as resonance energies of organic molecules, e.g. benzene. The Essay ends by arguing that CSBs are a distinct family of bonding, with a potential to bring about a Renaissance in the mental map of the chemical bond, and to contribute to productive chemical diversity. [ABSTRACT FROM AUTHOR]

This article, titled "From an Isolable Bismolyl Anion to an Yttrium-Bismolyl Complex with μ-Bridging Bismuth(I) Centers and Polar Covalent Y-Bi Bonds," discusses the discovery of a new bismolyl ligand and its interaction with yttrium metallocene cations. The ligand forms a bridge between two yttrium cations, creating a rare-earth bismolyl complex. The study also highlights the redox activity of the yttrium bismolyl complex. The article provides more detailed information on this research, which was conducted by S. Demir and co-workers. [Extracted from the article]

We have quantum chemically explored the gas-phase hydride affinities (HA) of archetypical cationic Lewis acids across the periodic table, using relativistic density functional theory (DFT) at ZORA-BP86/QZ4P. One purpose of this work is to establish an intrinsically consistent set of values of the 298 K HAs of all cationic maingroup-element hydrides (XHn–1+) in which we have varied the central atom X along groups 14–17 and periods 2–6. Our main purpose is to understand the emerging trends in HA values in terms of the underlying bonding mechanism using Kohn-Sham molecular orbital (MO) theory together with a quantitative bond energy decomposition analysis (EDA).

We have quantum chemically investigated the origin of the atypical blueshift of the H-C bond stretching frequency in the hydrogen-bonded complex X - •••H 3 C-Y (X, Y=F, Cl, Br, I), as compared to the corresponding redshift occurring in Cl - •••H 3 N and Cl - •••H 3 C-H, using relativistic density functional theory (DFT) at ZORA-BLYP-D3(BJ)/QZ4P. Previously, this blueshift was attributed, among others, to the contraction of the H-C bonds as the H 3 C moiety becomes less pyramidal. Herein, we provide quantitative evidence that, instead, the blueshift arises from a direct and strong X - •••C interaction of the HOMO of A - with the backside lobe on carbon of the low-lying C-Y antibonding σ* LUMO of the H 3 C-Y fragment. This X - •••C bond, in essence a tetrel bond, pushes the H atoms towards a shorter H-C distance and makes the H 3 C moiety more planar. The blueshift may, therefore, serve as a diagnostic for tetrel bonding., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Bonding interactions and spin-orbit coupling in the topological insulator SrAg4Sb2 are investigated using DFT with orbital projection analysis. Ag-Ag delta bonding is a key ingredient in the topological insulating state because the 4dxy + 4dx2 -y2 delta antibonding band forms a band inversion with the 5s sigma bonding band. Spin-orbit coupling is required to lift d orbital degeneracies and lower the antibonding band enough to create the band inversion. These bonding effects are enabled by a longer-than-covalent Ag-Ag distance in the crystal lattice, which might be a structural characteristic of other transition metal based topological insulators. A simplified model of the topological bands is constructed to capture the essence of the topological insulating state in a way that may be engineered in other materials., (© 2023 Wiley-VCH GmbH.)