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The boron atoms react with carbon monoxide and dinitrogen forming the end‐on bonded NNBCO complex in solid neon or in nitrogen matrices. The NNBCO complex rearranges to the (η2‐N2)BCO isomer with a more activated side‐on bonded dinitrogen ligand upon visible light excitation. (η2‐N2)BCO and its weakly CO‐coordinated complexes further isomerize to the NBNCO and B(NCO)2 molecules with N−N bond being completely cleaved under UV light irradiation. The geometries, energies and vibrational spectra of the molecules are calculated with quantum chemical methods and the electronic structures are analyzed with charge‐ and energy‐partitioning methods. [ABSTRACT FROM AUTHOR]

Two structural isomers containing five second‐row element atoms with 24 valence electrons were generated and identified by matrix‐isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet‐state boron cation with an electron configuration of (2s)0(2pσ)0(2pπ)2 and the CO/NO− ligands in the triplet state forming two degenerate electron‐sharing π bonds and two ligand‐to‐boron dative σ bonds. [ABSTRACT FROM AUTHOR]

The syntheses of the two novel complexes [Ag{Mo/W(CO)6}2]+[F‐{Al(ORF)3}2]− (RF=C(CF3)3) are reported along with their structural and spectroscopic characterization. The X‐ray structure shows that three carbonyl ligands from each M(CO)6 fragment bend towards the silver atom within binding Ag−C distance range. DFT calculations of the free cations [Ag{M(CO)6}2]+ (M=Cr, Mo, W) in the electronic singlet state give equilibrium structures with C2 symmetry with two bridging carbonyl groups from each hexacarbonyl ligand. Similar structures with C2 symmetry (M=Nb) and D2 symmetry (M=V, Ta) are calculated for the isoelectronic group 5 anions [Ag{M(CO)6}2]− (M=V, Nb, Ta). The electronic structure of the cations is analyzed with the QTAIM and EDA‐NOCV methods, which provide detailed information about the nature of the chemical bonds between Ag+ and the {M(CO)6}2q (q = −2, M = V, Nb, Ta; q = 0, M = Cr, Mo, W) ligands. [ABSTRACT FROM AUTHOR]

The synthesis of three complex series of the form [AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N‐donor molecules. Structure determination by single‐crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An−Cl and An−N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An−O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An−N and An−Cl bonds, as well as the highest degree of covalency of the An−O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties. [ABSTRACT FROM AUTHOR]

When carbonyl ligands coordinate to transition metals, their bond distance either increases (classical) or decreases (nonclassical) with respect to the bond length in the isolated CO molecule. C−O expansion can easily be understood by π‐back‐donation, which results in a population of the CO's π*‐antibonding orbital and hence a weakening of its bond. Nonclassical carbonyl ligands are less straightforward to explain, and their nature is still subject of an ongoing debate. In this work, we studied five isoelectronic octahedral complexes, namely Fe(CO)62+, Mn(CO)6+, Cr(CO)6, V(CO)6− and Ti(CO)62−, at the ZORA‐BLYP/TZ2P level of theory to explain this nonclassical behavior in the framework of Kohn–Sham molecular orbital theory. We show that there are two competing forces that affect the C−O bond length, namely electrostatic interactions (favoring C−O contraction) and π‐back‐donation (favoring C−O expansion). It is a balance between those two terms that determines whether the carbonyl is classical or nonclassical. By further decomposing the electrostatic interaction ΔVelstat into four fundamental terms, we are able to rationalize why ΔVelstat gives rise to the nonclassical behavior, leading to new insights into the driving forces behind C−O contraction. [ABSTRACT FROM AUTHOR]

The reactions of laser‐ablated beryllium atoms with dinitrogen and carbon monoxide mixtures form the end‐on bonded NNBeCO and side‐on bonded (η2‐N2)BeCO isomers in solid argon, which are predicted by quantum chemical calculations to be almost isoenergetic. The end‐on bonded complex has a triplet ground state while the side‐on bonded isomer has a singlet electronic ground state. The complexes rearrange to the energetically lowest lying NBeNCO isomer upon visible light excitation, which is characterized to be an isocyanate complex of a nitrene derivative with a triplet electronic ground state. A bonding analysis using a charge‐ and energy decomposition procedure reveals that the electronic reference state of Be in the NNBeCO isomers has an 2s02p2 excited configuration and that the metal‐ligand bonds can be described in terms of N2→Be←CO σ donation and concomitant N2←Be→CO π backdonation. The results demonstrate that the activation of N2 with the N−N bond being completely cleaved can be achieved via coupling with carbon monoxide mediated by a main group atom. [ABSTRACT FROM AUTHOR]

By means of first-principles calculations based on the density functional theory (DFT), we have investigated the structural, elastic, electronic, and bonding properties of three SrTi 1 - x Zr x O 3 alloys. The study shows that the substitution of Ti ion by the Zr one can also be undertaken by a tetragonal structure. However, due to the similar ionic radii between substitute cation, the choice of this super-cell leads to a weak change in both structural and dynamical properties and behave similarly even under different applied strains. Electronic as well as bonding properties are more affected by the substitution due to the rearrangement of the atomic orbitals. The calculations of band gaps depict a possible use of the investigated alloys in many UV device applications. Additionally, we will show that deep insight of bonding properties depicts some difference in ionicity degree between alloys. This trend is due essentially to the change in electron valence resulted in a weak variation of energetic orbitals. [ABSTRACT FROM AUTHOR]

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6+ and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable. [ABSTRACT FROM AUTHOR]

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6+ and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable. [ABSTRACT FROM AUTHOR]

Three‐coordinate cationic bismuth compounds [Bi(diaryl)(EPMe3)][SbF6] have been isolated and fully characterized (diaryl=[(C6H4)2C2H2]2−, E=S, Se). They represent rare examples of molecular complexes with Bi⋅⋅⋅EPR3 interactions (R=monoanionic substituent). The 31P NMR chemical shift of EPMe3 has been found to be sensitive to the formation of LA⋅⋅⋅EPMe3 Lewis acid/base interactions (LA=Lewis acid). This corresponds to a modification of the Gutmann–Beckett method and reveals information about the hardness/softness of the Lewis acid under investigation. A series of organobismuth compounds, bismuth halides, and cationic bismuth species have been investigated with this approach and compared to traditional group 13 and cationic group 14 Lewis acids. Especially cationic bismuth species have been shown to be potent soft Lewis acids that may prefer Lewis pair formation with a soft (S/Se‐based) rather than a hard (O/N‐based) donor. Analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations. [ABSTRACT FROM AUTHOR]

We present a systematic study on structural, electronic, optical properties of C30 fullerene and its six doped counterparts, C10X10Y10 (where, X=B, Al and Y=N, P, As) based on density functional theory calculation. All the fullerenes are energetically stable with cohesive energy per atom ranging from −5 to −8 eV. Chemical reactivity parameters are significantly enhanced due to doping. Further, nonlinear optics reveal that dopants bring remarkable change in polarizability and first hyperpolarizability of C30 derivatives. This work ensures the important implementations of these systems in nonlinear optics as well as for designing optical protective materials. Finally, the electronic absorption spectra predict the possibility of using C30 and heterofullerenes as photocatalyst in the visible region and UV light protection material in the UV region. [ABSTRACT FROM AUTHOR]

We present a systematic study on structural, electronic, optical properties of C30 fullerene and its six doped counterparts, C10X10Y10 (where, X=B, Al and Y=N, P, As) based on density functional theory calculation. All the fullerenes are energetically stable with cohesive energy per atom ranging from −5 to −8 eV. Chemical reactivity parameters are significantly enhanced due to doping. Further, nonlinear optics reveal that dopants bring remarkable change in polarizability and first hyperpolarizability of C30 derivatives. This work ensures the important implementations of these systems in nonlinear optics as well as for designing optical protective materials. Finally, the electronic absorption spectra predict the possibility of using C30 and heterofullerenes as photocatalyst in the visible region and UV light protection material in the UV region. [ABSTRACT FROM AUTHOR]

We reply to the comment by S. Pan and G. Frenking who challenged our interpretation of the Na−:→BH3 dative bond in the recently synthesized NaBH3− cluster. Our conclusion remains the same as that in our original paper (https://doi.org/10.1002/anie.201907089 and https://doi.org/10.1002/ange.201907089). This conclusion is additionally supported by the energetic pathways and NBO charges calculated at UCCSD and CASMP2(4,4) levels of theory. We also discussed the suitability of the Laplacian of electron density (QTAIM) and Adaptive Natural Density Partitioning (AdNDP) method for bond type assignment. It seems that AdNDP yields more sensible results. This discussion reveals that the complex realm of bonding is full of semantic inconsistencies, and we invite experimentalists and theoreticians to elaborate this topic and find solutions incorporating different views on the dative bond. [ABSTRACT FROM AUTHOR]

We challenge the interpretation of the chemical bond in NaBH3− proposed by Liu et al. We argue that NaBH3− has an electron‐sharing Na−BH3− covalent bond rather than a dative bond Na−→BH3. [ABSTRACT FROM AUTHOR]

Crystals of the rare earth metal polytelluride LaTe1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour‐assisted crystallization with iodine. The two‐dimensionally incommensurately modulated crystal structure has been investigated by X‐ray diffraction experiments. In contrast to the tetragonal average structure with unit‐cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group–subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e.Pmmn(α,β,)000(−α,β,)000 (No. 59.2.51.39) and Pm21n(α,β,)000(−α,β,)000 (No. 31.2.51.35), with modulation wave vectors q1 = αa* + βb* + c* and q2 = −αa* + βb* + c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI‐D)‐based bonding analysis on three different approximants. The temperature‐dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV. [ABSTRACT FROM AUTHOR]

The complexes of helium with nearly 30 neutral molecules (M) were investigated by various techniques of bonding analysis and symmetry‐adapted perturbation theory (SAPT). The main investigated function was the local electron energy density H(r), analyzed, in particular, so to estimate the degree of polarization (DoP) of He in the various He(M). As we showed recently (Borocci et al., J. Comput. Chem., 2019, 40, 2318–2328), the DoP is a quantitative index that is generally informative about the role of polarization (induction plus charge transfer [CT]) and dispersion in noncovalent noble gas complexes. As further evidence in this regard, we presently ascertained quantitative correlations between the DoP(He) of the He(M) and indices based on the electron density ρ(r), including the molecular electrostatic potential at the HeM bond critical point, as well as the percentage contributions of induction and dispersion to the SAPT binding energies. Based also on the explicit evaluation of the CT, accomplished through the study of the charge‐displacement function, we derived a quantitative scale that ranks the He(M) according to their dispersive, inductive, and CT bonding character. Our taken approach could be conceivably extended to other types of noncovalent complexes. [ABSTRACT FROM AUTHOR]

The structure, stability, and bonding character of some exemplary LAr and L-ArBeO (L = He, Ne, Ar, N2, CO, F2, Cl2, ClF, HF, HCl, NH3) were investigated by MP2 and coupled-cluster calculations, and by symmetry-adapted perturbation theory. The nature of the stabilizing interactions was also assayed by the method recently proposed by the authors to classify the chemical bonds in noble-gas compounds. The comparative analysis of the LAr and L-ArBeO unraveled geometric and bonding effects peculiarly related to the σ-hole at the Ar atom of ArBeO, including the major stabilizing/destabilizing role of the electrostatic interactionensuing from the negative/positive molecular electrostatic potential of L at the contact zone with ArBeO. The role of the inductive and dispersive components was also assayed, making it possible to discern the factors governing the transition from the (mainly) dispersive domain of the LAr, to the σ-hole domain of the L-ArBeO. Our conclusions could be valid for various types of non-covalent interactions, especially those involving σ-holes of respectable strength such as those occurring in ArBeO.

We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n−1)d AOs of M and strong backdonation from the occupied (n−1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals. [ABSTRACT FROM AUTHOR]

The bonding character of the noncovalent complexes of the noble‐gas (Ng) atoms ranges from nearly purely dispersive contacts to interactions featuring appreciable contributions of induction and charge transfer. In this study, we discuss a new quantitative index that seems peculiarly informative about these diverse bonding situations. This index was termed as the degree of polarization (DoP) of Ng, as it measures, in essence, the Ng polarization promoted by the binding partner. The definition of the DoP(Ng) relies on the analysis of the local electron energy density H(r), and its physical meaning was best appreciated by studying also the charge‐displacement function and the molecular electrostatic potential of the investigated benchmark species, that include nearly 60 Ngs complexes of different bonding character. The DoP(Ng) appears of general applicability, and is also positively correlated with other bonding character indices. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

To realize the efficient frequency conversion, the nonlinear ultraviolet crystal must exhibit strong second harmonic generation and possible phase-matching condition. The current first principles calculations predict that SrBi 2 B 2 O 7 represents potentially a new class of materials with such characteristics. For this aim, we present the first analysis of dynamical, bonding, linear and nonlinear optical properties of the SrBi 2 B 2 O 7 single crystal. To untangle such properties, both density functional theory calculation and topological analysis were used. It is found that the compound exhibits a wide indirect band gap and an interesting bonding motif. In particular, the distortion caused by the stereochemically active lone pair of the s -state in the Bi3+ unit favors the enhancement of local dipole moment. In addition, the refraction index, absorption spectrum, phase matching and second harmonic properties were calculated and analyzed. According to the results, SrBi 2 B 2 O 7 has a large d 33 s-order susceptibility component which makes it a very promising UV nonlinear optical material. • First ab intio calculations on the SrBi 2 B 2 O 7 crystal are presented. • Lattice parameters, band gap, phase matching and dipole moments are in agreement withexperimental data. • Electron localization function are used to analyze the bonding properties. • Second harmonic generation (SHG) properties are also calculated. • SHG are found very sensible to the combined effects of the SrO 6 /BiO 3 units. [ABSTRACT FROM AUTHOR]

We report a Na:−→B dative bond in the NaBH3− cluster, which was designed on the principle of minimum‐energy rupture, prepared by laser vaporization, and characterized by a synergy of anion photoelectron spectroscopy and electronic structure calculations. The global minimum of NaBH3− features a Na−B bond. Its preferred heterolytic dissociation conforms with the IUPAC definition of dative bond. The lone electron pair revealed on Na and the negative Laplacian of electron density at the bond critical point further confirm the dative nature of the Na−B bond. This study represents the first example of a Lewis adduct with an alkalide as the Lewis base. [ABSTRACT FROM AUTHOR]

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. [ABSTRACT FROM AUTHOR]

The combination of experimental and theoretical investigation of two new Pt-rich intermetallic compounds: APt 8 P 2 (A = Ca and La) is presented, including solid-state synthesis, crystal structure determination, physical properties characterization and chemical bonding analysis. APt 8 P 2 was obtained through the high-temperature pellet synthesis. According to both single crystal and powder X-ray diffraction results, APt 8 P 2 crystallize in the monoclinic DyPt 8 P 2 -type structure with space group I 2/ m (S.G. 12). Crystal structure of APt 8 P 2 can be considered as intercalating multiple Pt layers into APt 2 P 2. Magnetic susceptibility measurement indicates diamagnetism of both compounds. The specific heat down to 1.8 K shows no evidence for bulk superconductivity in either CaPt 8 P 2 and LaPt 8 P 2. Electronic structure calculations match well with the observed structural stability and metallic behavior. The following Crystal Orbital Hamiltonian Population (-COHP) calculations suggest that the difference of Pt-Pt antibonding interaction could be the key factor that results in the shrinkage of c axis in APt 8 P 2. • Two new intermetallics APt 8 P 2 (A = Ca and La) were synthesized and characterized. • A full bonding analysis of APt 8 P 2 was taken and proves the structural stability. • Electronic structure calculation and heat capacity measurement match well. • No superconductivity can be found above 2 K. • APt 8 P 2 (A = Ca and La) show diamagnetism under magnetic field of 9 T. [ABSTRACT FROM AUTHOR]

Phosphaheteroallenes R−P=C=L, with L = N‐heterocyclic carbenes (NHCs), can be viewed to a certain extent as phosphaisonitriles stabilized with NHCs, R−P=C:←L. The suitability of these molecules as ligands for coinage‐metal ions was investigated and coordination through the central carbon center was observed in most cases. A combination of experiments, spectroscopic methods, and DFT calculations indicates the presence of a hidden electron pair at the carbon center of R−P=C:←L. Remarkably, this lone pair also inserts intramolecularly in C−H bonds showing the carbene‐type reactivity which is expected for phosphaisonitriles. [ABSTRACT FROM AUTHOR]

To explore the mechanisms for Ni-based oxide-catalyzed oxidative dehydrogenation (ODH) reactions, we investigate the reactions of C2H6 with NiO+ using density functional calculations. Two possible reaction pathways are identified, which lead to the formation of ethanol (path 1), ethylene and water (path 2). The proportion of products is discussed by Curtin-Hammett principle, and the result shows that path 2 is the main reaction channel and the water and ethylene are the main products. In order to get a deeper understanding of the titled reaction, numerous means of analysis methods including the atoms in molecules (AIM), electron localization function (ELF), natural bond orbital (NBO), and density of states (DOS) are used to study the properties of the chemical bonding evolution along the reaction pathways. [ABSTRACT FROM AUTHOR]

We report the high‐pressure structural characterization of an organic polyiodide salt in which a progressive addition of iodine to triiodide groups occurs. Compression leads to the initial formation of discrete heptaiodide units, followed by polymerization to a 3D anionic network. Although the structural changes appear to be continuous, the insulating salt becomes a semiconducting polymer above 10 GPa. The features of the pre‐reactive state and the polymerized state are revealed by analysis of the computed electron and energy densities. The unusually high electrical conductivity can be explained with the formation of new bonds. [ABSTRACT FROM AUTHOR]

The lanthanide octacarbonyl anion complexes Ln(CO)8− (Ln=Tm, Yb, Lu) were produced in the gas phase and detected by mass‐selected infrared photodissociation spectroscopy in the carbonyl stretching‐frequency region. By comparison of the experimental CO‐stretching frequencies with calculated data, which are strongly red‐shifted with respect to free CO, the Yb(CO)8− and Lu(CO)8− complexes were determined to possess octahedral (Oh) symmetry and a doublet X2A2u (Yb) and singlet X1A1g (Lu) electronic ground state, whereas Tm(CO)8− exhibits a D4h equilibrium geometry and a triplet X3B1g ground state. The analysis of the electronic structures revealed that the metal‐CO attractive forces come mainly from covalent orbital interactions, which are dominated by [Ln(d)]→(CO)8 π backdonation and [Ln(d)]←(CO)8 σ donation (contributes ≈77 and 16 % to covalent bonding, respectively). The metal f orbitals play a very minor role in the bonding. The electronic structure of all three lanthanide complexes obeys the 32‐electron rule if only those electrons that occupy the valence orbitals of the metal are considered. Follow the rules: The lanthanide anion complexes Ln(CO)8− (Ln=Tm, Yb, Lu) were experimentally observed and spectroscopically characterized in the gas phase. The metal–CO bonds were easily understood in terms of donor–acceptor interactions. The bonding situation follows the 32‐electron rule if the symmetry of the orbitals is taken into account. The dominant valence functions of the lanthanide atoms are the d orbitals, the stabilizing contribution of the f functions is very small. [ABSTRACT FROM AUTHOR]

Abstract In order to gain an insight into the bonding and to characterize linear and nonlinear optical properties of three infrared LiGaGe 2 S 6 , LiGaGe 2 Se 6 , and LiGaGe 2 Te 6 compounds, we performed an ab initio calculation based on density functional theory. The calculations determined lattice parameters, band gaps, dipole moments, and second harmonic components that commonly agreed well with the available experimental data. We show in this article, through a large body of calculations, the trend in the row of participating anions, S ⟶ Se ⟶ Te, enhances the polarization effect and the coordination structure distortions in the polyhedra groups forming the bonding pattern of the cell. This one also affects both the electronic and the optical properties, making the compounds more propitious for device-based optical applications. [ABSTRACT FROM AUTHOR]

Extensive explorations of their potential energy surfaces, combined with high‐level quantum chemical computations, strikingly show that the lowest energy structures of the (Li6Si5)2–5 systems consist of 2–5 Si56− aromatic units, surrounded by Li+ counterions, respectively. These viable gas‐phase compounds are the pioneering reported cases of oligomers made by planar aromatic silicon rings. Based on the key evidence that these oligomers are energetically favored, and that their silicon rings aromaticity is thoroughly preserved, the Li6Si5 cluster is proposed as a potential assembly unit to build silicon‐lithium nanostructures, thus opening new paths to design Zintl compounds at the nanoscale level. Aromatic building blocks: After a systematic exploration of the potential energy surface of the (Li6Si5)2–5 clusters, it was found that the lowest energy structures in all cases are formed by multiple aromatic Si56− pentagonal units interacting electrostatically with lithium cations. These units maintain their geometric and electronic properties as revealed by chemical bonding and magnetic response analyses. [ABSTRACT FROM AUTHOR]

The alkali metal‐nickel carbonyl anions ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3− fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. 18‐electron transition‐metal complexes: ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The calculated equilibrium structures possess C3v geometry and the analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. [ABSTRACT FROM AUTHOR]

The alkali metal‐nickel carbonyl anions ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3− fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. 18‐electron transition‐metal complexes: ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The calculated equilibrium structures possess C3v geometry and the analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. [ABSTRACT FROM AUTHOR]

The factors responsible for the enhancement of the halogen bond by an adjacent hydrogen bond have been quantitatively explored by means of state-of-the-art computational methods. It is found that the strength of a halogen bond is enhanced by ca. 3 kcal/mol when the halogen donor simultaneously operates as a halogen bond donor and a hydrogen bond acceptor. This enhancement is the result of both stronger electrostatic and orbital interactions between the XB donor and the XB acceptor, which indicates a significant degree of covalency in these halogen bonds. In addition, the halogen bond strength can be easily tuned by modifying the electron density of the aryl group of the XB donor as well as the acidity of the hydrogen atoms responsible for the hydrogen bond.

The structure, stability, and bonding character of fifteen (Ng-H-Ng)+ and (Ng-H-Ng’)+ (Ng, Ng’ = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng’. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)+ and (Ng-H-Ng’)+. The Ng-H and Ng’-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.

[Display omitted] • Structure, stability and bonding character of the NgBz (Ng = He-Xe; Bz = B 3 N 3 H 6). • The NgBz are describable as complexes of Ng ligated to one, two, or three N atoms. • The stability of the NgBz increases in the order N-mono < N-di < N-three. • The stability of the NgBz is determined mainly by the dispersive interaction. • The NgBz are compared with other investigated complexes of Ng with larger BN sheets. The complexes of He, Ne, Ar, Kr and Xe with B 3 N 3 H 6 were investigated by MP2, CCSD(T), and SAPT ab initio methods, and accurate procedures of bonding analysis. These systems are describable as mono-, di-, and tri-coordinated to the N atoms, their stabilities following the order N-mono < N-di < N-tri. The binding energies are within 1 or 2 kcal mol−1, and the interactions are dominated by the dispersion. The results are compared with those obtained recently from a DFT study on the complexes of He, Ne, Ar, and Kr with larger BN sheets [Phys. Chem. Chem. Phys. 24 (2022) 2554–2566.]. [ABSTRACT FROM AUTHOR]

Spin polarized density functional theory computation was performed to elucidate electronic effects based on first-row transition metal substituted Fe 5 C 2 (100) surfaces for oxygen removal. The results indicate that on Cr/Mn substituted surfaces, oxygen removal predominantly takes place through the CO 2 path. However, on Cu substituted surfaces, there is a tendency for the system to favor the H 2 O path. These findings demonstrate the possibility of manipulating oxygen removal pathways by leveraging electronic effects. [Display omitted] • Higher electronegativity metals have been found to facilitate the removal of surface oxygen. • The linear correlation has been established between the energy barrier and the electronegativity of the substituted metal. • The insights gained from the study enable the manipulation of oxygen removal pathways by leveraging electronic effects. • The study offers a strategy for the construction of durable catalysts by considering the perspective of oxygen removal. This study employed spin-polarized density functional theory and investigated the removal of surface oxygen on Fe 5 C 2 (100) surfaces substituted with first-row transition metals. It was observed that the substituted metals with lower electronegativity, such as Cr and Mn, could hinder the removal of surface oxygen. Conversely, substituted metals with higher electronegativity, such as Co, Ni, and Cu, facilitates the removal of surface oxygen. The results revealed a clear correlation between the energy barrier for oxygen removal and the electronegativity of substituted metals, which provides a straightforward and efficient approach to estimate the energy barrier for oxygen removal on iron carbide surfaces. Furthermore, the study demonstrated that the oxygen removal pathway is dependent on the electronegativity of substituted metals. For Cr and Mn substituted surfaces (low electronegativity), the oxygen removal via CO 2 pathway is preferable both in thermodynamics and kinetics, while for Cu substituted surfaces (high electronegativity), the hydrogenation of O to H 2 O is more favorable. These findings reveal the significance of electronic promoters in catalyst design. [ABSTRACT FROM AUTHOR]

• The nature of metal-dichalcogenolate bond is studied theoretically. • The different types of interaction energies between the fragments are calculated. • Contributions of the electrostatic interactions are more than the orbital. • The orbital interactions are mainly Ni←L σ-donation. • The orbital interactions show an opposite trend with the interaction energies. In this work, the interactions between the fragments in homoleptic square-planar d8 metal bis(1,2-dichalcogenolate) complexes [M(E 2 C 2 (CN) 2) 2 ]2– (E = S , Se, Te; M =Ni(II), Pd(II), Pt(II)) have been investigated by using density functional theory (BP86, M06) calculations with a focus on the nature of metal−dichalcogenolate bonds. Four types of interaction energies between the fragments, the deformation energies of metal and dichalcogenolate ions as well as the total interaction and stabilization energies of the complexes were calculated and compared. An energy decomposition analysis (EDA) was also performed to study the nature of metal−bis(dichalcogenolate) bonds in these complexes. The results showed that the stabilization and total interaction energies are decreased by changing the chalcogen atom from sulfur to selenium and from selenium to tellurium ([M(S 2 C 2 (CN) 2) 2 ]2– > [M(Se 2 C 2 (CN) 2) 2 ]2– > [M(Te 2 C 2 (CN) 2) 2 ]2–). The analysis of metal−bis(dichalcogenolate) bonds showed that the orbital interactions are mainly Metal←Lσ and have considerably less contribution to the total attractive interactions compared to electrostatic interactions. However, the contribution of orbital interactions, in an opposite trend with the interaction energies, is increased by changing the chalcogen atom from sulfur to selenium and from selenium to tellurium. Nature and strength of metal-dichalcogenolate bond in homoleptic square-planar d8 metal bis(1,2-dichalcogenolate) complexes [M(E 2 C 2 (CN) 2) 2 ]2– (E = S , Se, Te; M =Ni(II), Pd(II), Pt(II)): A DFT study. [Display omitted] [ABSTRACT FROM AUTHOR]

Developing novel nanoscale carriers for drug delivery is of great significance for improving treatment efficiency and reducing side effects of antitumor drugs. In view of the good biocompatibility and special affinity of porphyrin (PP) molecule to cancer cells, it was used to construct a series of metal-doped M@PP (M = Ca ∼ Zn) materials for the delivery of anticancer drug 5-fluorouracil (5-Fu) in this work. Our results reveal that 5-Fu is tightly adsorbed on M@PP (M = Ca ∼ V, Mn ∼ Co, and Zn) by chemisorption, but is physically adsorbed by M@PP (M = Cr, Ni, and Cu). The calculated electronic properties show that all these 5-Fu@[M@PP] (M = Ca ∼ Zn) complexes have both high stability and solubility. Among these 5-Fu@[M@PP] complexes, the chemical bond formed between 5-Fu and Ti@PP has the strongest covalent characteristic, resulting in the largest adsorption energy of −19.93 kcal/mol for 5-Fu@[Ti@PP]. In particular, 5-Fu@[Ti@PP] has the proper recovery time under the near-infrared light at body temperature, which further suggests that Ti@PP is the best drug carrier for 5-Fu. This study not only reveals the interaction strength and nature between 5-Fu and M@PP, but also confirmed the intriguing potential of Ti@PP as nano-carrier for drug delivery. However, further experimental research should be conducted to verify the conclusion obtained in this work. [Display omitted] • Eleven metal-substituted metalloporphyrins M@PP (M = Ca ∼ Zn) was screened for the 5-Fu delivery. • Ti@PP is proved to be the best carrier for 5-Fu among these studied M@PP (M = Ca ∼ Zn) materials. • The interaction nature between 5-Fu and M@PP was revealed by analyzing different parameters obtained by the DFT calculations. • 5-Fu is strongly adsorbed to the Ti site of Ti@PP via forming strong polar covalent bond. • 5-Fu can be quickly released from Ti@PP under the near-infrared light at body temperature. [ABSTRACT FROM AUTHOR]

The aim of this review is threefold. On the one hand, we intend it to serve as a gentle introduction to the Interacting Quantum Atoms (IQA) methodology for those unfamiliar with it. Second, we expect it to act as an up-to-date reference of recent developments related to IQA. Finally, we want it to highlight a non-exhaustive, yet representative set of showcase examples about how to use IQA to shed light in different chemical problems. To accomplish this, we start by providing a brief context to justify the development of IQA as a real space alternative to other existent energy partition schemes of the non-relativistic energy of molecules. We then introduce a self-contained algebraic derivation of the methodological IQA ecosystem as well as an overview of how these formulations vary with the level of theory employed to obtain the molecular wavefunction upon which the IQA procedure relies. Finally, we review the several applications of IQA as examined by different research groups worldwide to investigate a wide variety of chemical problems.

We show that natural bond orbital (NBO) and natural resonance theory (NRT) analysis methods provide both optimized Lewis-structural bonding descriptors for ground-state electronic properties as well as suitable building blocks for idealized “diabatic” two-state models of the associated spectroscopic excitations. Specifically, in the framework of single-determinant Hartree-Fock or density functional methods for a resonance-stabilized molecule or supramolecular complex, we employ NBO/NRT descriptors of the ground-state determinant to develop a qualitative picture of the associated charge-transfer excitation that dominates the valence region of the electronic spectrum. We illustrate the procedure for the elementary bond shifts of SN2-type halide exchange reaction as well as the more complex bond shifts in a series of conjugated cyanine dyes. In each case, we show how NBO-based descriptors of resonance-type 3-center, 4-electron (3c/4e) interactions provide simple estimates of spectroscopic excitation energy, bond orders, and other vibronic details of the excited-state PES that anticipate important features of the full multi-configuration description. The deep 3c/4e connections to measurable spectral properties also provide evidence for NBO-based estimates of ground-state donor-acceptor stabilization energies (sometimes criticized as “too large” compared to alternative analysis methods) that are also found to be of proper magnitude to provide useful estimates of excitation energies and structure-dependent spectral shifts.

Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation.

Quantum chemical calculations using density functional theory at the BP86‐D3(BJ)/def2‐TZVPP level of theory are reported for transition metal compounds [TM]‐L in high and low oxidation states involving carbene, carbyne, alkene, and alkyne ligands L. The nature of the [TM]‐L bond is analyzed with the energy decomposition analysis ‐ natural orbitals for chemical valence (EDA‐NOCV) method. The calculations reveal that transition metal compounds with ligands, that are typically classified as donor–acceptor complexes possessing dative bonds (Fischer‐type carbenes and carbynes, alkene, and alkyne complexes) or as TM compounds with electron‐sharing bonds (Schrock‐type carbenes and carbynes, metallacyclopropanes, and metallacyclopropenes), exhibit significant differences between the orbital interactions when closed‐shell or open shell fragments are used. Fischer‐type carbene complexes have much lower orbital interaction (ΔEorb) values when singlet fragments are employed compared to triplet fragments. In contrast, singlet and triplet fragments of Schrock‐type carbene complexes give similar ΔEorb values. The best description for Fischer‐type carbyne complexes is found for neutral fragments in their electronic doublet state, which engage in a mixture of dative bonding (σ donation and π backdonation) and one electron‐sharing π bond. The EDA‐NOCV calculations of Schrock‐type carbynes using open‐shell species in their quartet electronic state give similar ΔEorb values as neutral fragments in their electronic doublet state. Alkene and alkyne complexes, but also metallacyclic species, are best described with singlet fragments, but the difference between the ΔEorb values for dative bonding and electron‐sharing bonding using triplet fragments becomes much smaller for molecules that are considered as metallacycles. © 2018 Wiley Periodicals, Inc. EDA‐NOCV calculations are employed to distinguish between electron sharing and dative interactions in transition metal–ligand bonds and to visualize the associated pairwise orbital interactions. [ABSTRACT FROM AUTHOR]

Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd‐Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te2 dumbbells and linear Te3 units in accordance with ELI‐D based bonding analyses. The latter can be understood as a Te34– anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental/calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at TN = 12 K for TbTe1.8 and TN = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K. [ABSTRACT FROM AUTHOR]

DNA quadruplexes have been the subject of investigation because of their biological relevance and because of their potential application in supramolecular chemistry. Similarly, RNA quadruplexes are now gaining increasing attention. Although DNA and RNA quadruplexes are structurally very similar, the latter show higher stability. In this study we report dispersion‐corrected density functional theory (DFT‐D) quantum chemical calculations that were undertaken to understand the difference in stabilities of RNA and DNA quadruplexes. The smallest meaningful model of a stack of quartets, interacting with alkali metal cations, was simulated in an aqueous environment. The energy decomposition analysis allows for in‐depth examination of the interaction energies, emphasising the role of noncovalent interactions and better electrostatics in determining RNA‐GQs higher stabilities, particularly pinpointing the role of the extra 2′‐OH groups. Furthermore, our computations present new insights on why the cation is required for self‐assembly: unexpectedly the cation is not necessary to relieve the repulsion between the oxygen atoms in the central cavity, but it is needed to overcome the entropic penalty. Why so stable? Dispersion‐corrected (DFT‐D) quantum chemical calculations on the stabilities of RNA and DNA quadruplexes show electrostatic interactions and hydrogen bonds make the decisive difference (see figure). [ABSTRACT FROM AUTHOR]

We report the F2@C60 system as the first example of an endohedral fullerene in which C60 acts as a cation C60+ interacting with endohedral anion, F2−. Our state‐of‐the‐art computations reveal that in F2@C60, despite of the known high electron affinity of C60, an electron is transferred from C60 to F2 resulting in the F2−@C60+ system. The F−F bond length in F2@C60 is substantially longer than in free F2, which is the result of electron‐transfer to the antibonding σu molecular orbital of F2. Interestingly, although there is a full charge‐transfer of one electron between C60 and F2, only negligible delocalized covalent interactions are found between F2− and C60+ which is a reminiscent of ionic crystals. Therefore, F2−@C60+ can be considered as a single‐molecule crystal. The other encapsulated halogens in C60 do not show such behavior. Crystal ball: State‐of‐the‐art computations reveal that in F2@C60, despite of the high electron affinity of C60, an electron is transferred from C60 to F2 giving a F2−@C60+ system in the electronic triplet state. The F−F bond length is substantially longer than in free F2. There is negligible covalent interaction between encapsulated F2− and C60+ cage, a situation reminiscent of perfect ionic crystals. Thus this molecule can be named a single‐molecule crystal. [ABSTRACT FROM AUTHOR]

Covalency and ionicity are orthogonal rather than antipodal concepts. We demonstrate for the case of siloxane systems [R3Si−(O−SiR2)n−O−SiR3] that both covalency and ionicity of the Si−O bonds impact on the basicity of the Si‐O‐Si linkage. The relationship between the siloxane basicity and the Si−O bond character has been under debate since previous studies have presented conflicting explanations. It has been shown with natural bond orbital methods that increased hyperconjugative interactions of LP(O)→σ*(Si‐R) type, that is, increased orbital overlap and hence covalency, are responsible for the low siloxane basicity at large Si‐O‐Si angles. On the other hand, increased ionicity towards larger Si‐O‐Si angles has been revealed with real‐space bonding indicators. To resolve this ostensible contradiction, we perform a complementary bonding analysis, which combines orbital‐space, real‐space, and bond‐index considerations. We analyze the isolated disiloxane molecule H3SiOSiH3 with varying Si‐O‐Si angles, and n‐membered cyclic siloxane systems Si2H4O(CH2)n−3. All methods from quite different realms show that both covalent and ionic interactions increase simultaneously towards larger Si‐O‐Si angles. In addition, we present highly accurate absolute hydrogen‐bond interaction energies of the investigated siloxane molecules with water and silanol as donors. It is found that intermolecular hydrogen bonding is significant at small Si‐O‐Si angles and weakens as the Si‐O‐Si angle increases until no stable hydrogen‐bond complexes are obtained beyond φSiOSi=168°, angles typically displayed by minerals or polymers. The maximum hydrogen‐bond interaction energy, which is obtained at an angle of 105°, is 11.05 kJ mol−1 for the siloxane–water complex and 18.40 kJ mol−1 for the siloxane–silanol complex. Ionic or covalent? Maybe both: The general notion of covalency and ionicity as antipodal concepts is questioned based on a case study of siloxanes. A complementary bonding analysis, which combines orbital‐space, real‐space, and bond‐index considerations, was used to analyze the isolated disiloxane molecule H3SiOSiH3 with varying Si‐O‐Si angles, and n‐membered cyclic siloxane systems Si2H4O(CH2)n−3. All methods show that both covalent and ionic interactions increase simultaneously towards larger Si‐O‐Si angles. [ABSTRACT FROM AUTHOR]

The density functional theory calculations were performed to systematically investigate the reaction of Ni+ with ethyl acetate in the gas phase. The reactive sites and reactivity were predicted by the average local ionization energy (ALIE). All possible reaction pathways were identified, which led to the formation of ketene or ethanol, two acetal units, and acetic acid or ethylene. The product distribution was discussed by means of the Curtin-Hammett principle. In addition, the properties of the chemical bonding evolution along the reaction pathway were studied using various analysis methods including atoms in molecules (AIM) and natural bond orbital (NBO). The frontier molecular orbital interactions were analyzed. The calculation results confirm that there are three reaction paths, in which the path B is the most favorable path, and acetic acid or ethylene is the main product.ᅟ [ABSTRACT FROM AUTHOR]

The density functional theory calculations were performed to systematically investigate the reaction of Ni+ with ethyl acetate in the gas phase. The reactive sites and reactivity were predicted by the average local ionization energy (ALIE). All possible reaction pathways were identified, which led to the formation of ketene or ethanol, two acetal units, and acetic acid or ethylene. The product distribution was discussed by means of the Curtin-Hammett principle. In addition, the properties of the chemical bonding evolution along the reaction pathway were studied using various analysis methods including atoms in molecules (AIM) and natural bond orbital (NBO). The frontier molecular orbital interactions were analyzed. The calculation results confirm that there are three reaction paths, in which the path B is the most favorable path, and acetic acid or ethylene is the main product.ᅟ [ABSTRACT FROM AUTHOR]

Abstract: DFT calculations at the BP86+D3(BJ)/TZ2P level, with and without relativistic contributions, using the ZORA approximation have been carried out for the coinage metal carbonyl complexes [TM(CO)]+ and [TM(CO)2]+ with TM=Cu, Ag, Au. The nature of the metal‐CO interactions and the relativistic effects on the different energy terms were analyzed with the EDA‐NOCV method. The three terms Pauli repulsion, Coulomb attraction, and orbital interactions become stronger when relativistic effects are accounted for; the strengthening exhibits the order ΔEPauli>ΔEelstat>ΔEorb. The largest change in the calculated energy terms is, as expected, found for gold, followed by silver and copper. The relativistic contributions on the Cu+‐CO interactions are significant and thus, relativistic effects should not be neglected in quantum chemical calculations in copper compounds. Breakdown of the orbital term into individual contributions shows that the relativistic effect in [TM(CO)]+ is for the TM+←CO σ‐donation stronger than for TM+→CO π‐backdonation, except for TM=Cu. The trend in the dicarbonyls [TM(CO)2]+ has the order (+,+) σ‐donation > π‐backdonation > (+,−) σ‐donation. The bonding analysis reveals that there is a sizeable contribution from TM+→CO σ‐backdonation in all carbonyl complexes that further stabilizes the metal‐carbonyl bonds. In [Au(CO)2]+ it becomes even larger than the (+,−) OC→TM+←CO σ‐donation. The trends of the various orbital interactions and the effect of relativity on their strength can be understood when the valence orbitals of the metals and CO are considered. [ABSTRACT FROM AUTHOR]

Based on Density Functional Theory (DFT) calculations, the narrowed band gap of two-dimensional (2D) SiC planar structure was investigated under uniaxial strains applied along the zigzag and armchair directions. 2D SiC structure exhibits an indirect band gap in its pristine state which undergoes towards direct band gap at −10.35% compressive zigzag strain and vanishes below −16.87% leading to its metallization. The unidirectional strain, applied along the zigzag direction, induces the closure of Si C Si bond angle bending from 120 ° to 99 ° promoting the increase of the ionic character of the disynaptic (Si C) atomic basin while reducing the covalent character observed in the pristine structure as revealed by electron localization function (ELF). Additionally, the strain imposed along the zigzag direction, promotes the appearance of weak interactions in regions where there is no absence of strain by means of non-covalent interactions (NCI) index. These non-covalent interactions promote the stability of 2D SiC planar structure under strain regime as recently observed in its three dimensional counterpart (3C SiC). Our structural-electronic-bonding analysis shows that the band gap engineering can be monitored by unidirectional strain regime optimizing the narrowed band gap opening potential routes on the band gap engineering of 2D semiconductor materials with applications in the new generation of electronic devices. [ABSTRACT FROM AUTHOR]