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Zn-Zn bond as one of the metal-to-metal bonds in clusters and molecules is of fundamental interest in many areas of natural science. Neutral boronyl can be viewed as σ radical and has been found in the boronyl metal complexes. However, the complex with Zn-Zn bond stabilized by boronyl ligands has not been found so far. Herein, we report on the computational design of the simplest case of such a system: linear D∞h OBZnZnBO. The structural and electronic properties and chemical bonding on series of zinc complexes Znx(BO)y (x=1,2; y=1,2) with boronyl as ligands have been studied using quantum chemical calculations at the B3LYP and PBE0 level, respectively. For the Zn2(BO)2 cluster, the linear D∞h OBZnZnBO is the global minimum, in which the calculated Zn-Zn bond length of rZn-Zn = 2.400 A at B3LYP level, appears to be close to the latest recommended covalent radii (2.40 A) of the proposed single bond covalent radii of the Zn-Zn. Chemical bonding analyses show that D∞h OBZnZnBO possesses the linear four-center two-electron (4c-2e) σ bond. The σ bond framework has a contribution of Zn orbitals 54%, B orbitals 44%, which involves the Zn 4s 20% and 4p 34%, B 2s 28% and 2p 16%, respectively. Furthermore, the D∞h HZnZnH and NCZnZnCN clusters also exhibit one linear 4c-2e σ bond, due to the secondary contribution from the H s and C sp components, respectively. Linear 4c-2e σ bond greatly stabilizes the dizinc complexes. D∞h OBZnZnBO is thermochemically stable with respect to possible formation channel at room temperature, whereas the exergonic channel, 2ZnBO (C∞v, 2∑g)→OBZnZnBO (D∞h, 1∑g), the formation energy evaluated is -58.75 kcal mol1 at the B3LYP level. Thus D∞h OBZnZnBO as the first observation of Zn-Zn covalent bond in zinc complexes with boronyl as ligands may be synthesized in the laboratory in the near future.

Iako se u školi uče iznosi ionskih, van der Waalsovih i kovalentnih radijusa, ne uči se što oni zapravo jesu – školske definicije prikrivaju njihovu pravu, kvantnomehaničku prirodu. U radu je ispitano značenje definicija veličine atoma te opisan njihov izvod: iz elektronske gustoće (povezane s funkcijom koju zovemo atomskom orbitalom), iz duljine kovalentne veze i položaja jezgara, iz prvog virijalnog koeficijenta jednadžbe realnog plina te Lennard-Jonesova potencijala (van der Waalsov radijus). Iz navedenog se vidi da se veličina atoma ne može jednoznačno definirati ili, točnije, da se ne može govoriti o veličini atoma na isti način na koji se govori o veličini makroskopskih objekata. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., Despite the fact that atomic, i.e. Van der Waals, ionic, and covalent radii are commonplace in chemical textbooks, their real, quantum-mechanical nature is blurred by simplified scholar definitions. The size of an atom may be defined, and calculated, in many ways (from atomic orbital density, bond lengths, microwave spectra, virial coefficient, Lennard-Jones potential), but whatever is calculated, or defined, the obtained value cannot be properly compared to the size of a macroscopic object. This paper stresses the need that students understand the real nature of quantum-chemical models, and not confuse various representations of molecular structure (molecular models) with the real atoms and molecules. This work is licensed under a Creative Commons Attribution 4.0 International License.

Metal-insulator transition (MIT) compounds are materials that may exhibit insulating or metallic behavior, depending on the physical conditions, and are of immense fundamental interest owing to their potential applications in emerging microelectronics. There is a dearth of thermally-driven MIT materials, however, which makes delineating these compounds from those that are exclusively insulating or metallic challenging. Here we report a material database comprising temperature-controlled MITs (and metals and insulators with similar chemical composition and stoichiometries to the MIT compounds) from high quality experimental literature, built through a combination of materials-domain knowledge and natural language processing. We featurize the dataset using compositional, structural, and energetic descriptors, including two MIT relevant energy scales, an estimated Hubbard interaction and the charge transfer energy, as well as the structure-bond-stress metric referred to as the global-instability index (GII). We then perform supervised classification, constructing three electronic-state classifiers: metal vs non-metal (M), insulator vs non-insulator (I), and MIT vs non-MIT (T). We identify two important descriptors that separate metals, insulators, and MIT materials in a 2D feature space: the average deviation of the covalent radius and the range of the Mendeleev number. We further elaborate on other important features (GII and Ewald energy), and examine how they affect classification of binary vanadium and titanium oxides. We discuss the relationship of these atomic features to the physical interactions underlying MITs in the rare-earth nickelate family. Last, we implement an online version of the classifiers, enabling quick probabilistic class predictions by uploading a crystallographic structure file.

We systematically explore the stability and properties of [B12X11NG]- adducts resulting from the binding of noble gas atoms to anionic [B12X11]- clusters in the gas phase of mass spectrometers. [B12X11]- can be obtained by stripping one X- off the icosahedral closo-dodecaborate dianion [B12X12]2-. We study the binding of the noble gas atoms He, Ne, Ar, Kr, and Xe to [B12X11]- with substituents X = F, Cl, Br, I, and CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr, and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B12(CN)11Xe]-. The predicted B-NG equilibrium distance in the complexes with Ar, Kr, and Xe is only 0.10-0.25 A longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B12 cage is observed.

Cu2ZnSnSe4 (CZTSe) based solar cells, containing abundant elements, with Ag alloying have recently reached efficiency of 10.2%. The open circuit voltage in CZTSe devices is believed to be limited, in between other factors, by strong band tailing caused by an exceptionally high density of Cu/Zn antisites. By replacing Cu in CZTSe with Ag, whose covalent radius is 15% larger than that of Cu and Zn, the density of I–II antisite defects (e.g., Cu–Zn disorder) is predicted to drop. In the present work, (AgxCu1 – x)2ZnSnS4 (ACZTS) heterostructures in three different architectures were investigated. The 5 and 10% silver substituted CZTS absorber layers were obtained by low-cost spray pyrolysis technique, as well as three different methods for the CdS layer deposition were tested in order to optimize the ACZTS heterostructure efficiency.

The synthesis of a novel mono‐anionic phosphino‐amide ligand based on a xanthene backbone is reported, togetherr with the corresponding GaI complex, (PON)Ga (PON = 4‐(di(2,4,6‐trimethylphenyl)phosphino)‐5‐(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene). The solid‐state structure of (PON)Ga (obtained from X‐ray crystallography) reveals very weak O⋅⋅⋅Ga and P⋅⋅⋅Ga interactions, consistent with a R2NGa fragment which closely resembles those found in one‐coordinate amidogallium systems. Strong N‐to‐Ga π donation from the amido substituent is reflected in a very short N−Ga distance (1.961(2) Å), while the P⋅⋅⋅Ga contact (3.076(1) Å) is well outside the sum of the respective covalent radii. While the donor properties of the PON ligand towards GaI are highly unsymmetrical, oxidation to GaIII leads to much stronger coordination of the pendant phosphine as shown by P−Ga distances which are up to 20 % shorter. From a steric perspective, the PON ligand is shown to be significantly bulkier than related β‐diketiminate systems, a finding consistent with reactions of (PON)Ga towards O‐atom sources that proceed without oligomerization. Despite this, the enhanced P‐donor properties brought about by oxidation at gallium are not sufficient to quench the reactivity of the highly polar Ga−O unit. Instead, intramolecular benzylic C−H activation is observed across the Ga−O bond of a transient gallanone intermediate., The application of a sterically demanding mono‐anionic PON ligand in gallium chemistry has been probed, revealing a highly unsymmetrical donor profile towards GaI and structural features reminiscent of one‐coordinate gallium amides. Oxidation at the metal leads to a marked increase in the donor capabilities of the phosphine donor, although the transient gallanone formed by O‐atom transfer still undergoes facile C−H activation across the Ga−O bond.

By means of quantum chemistry, it is established that tungsten and rhenium are most effective alloying elements capable of increasing the resistance of aluminum alloys to hydrogen-induced embrittlement. Tungsten (W) and rhenium (Re) atoms produce strong compression of aluminum lattice, while having sufficiently large covalent radii. In addition, each W and Re atom forms stable chemical bonds with 12 surrounding Al atoms. As a result, W and Re dopants strongly bind Al atoms, thus significantly increasing the energy of vacancy formation and suppressing the process of hydrogen-induced embrittlement. The main mechanical properties of the most hydrogen-resistant aluminum compound, WReAl24, have been calculated using the density functional theory.

A problem of identification of parameters of the Mie–Lennard-Jones and Morse pairwise interatomic potentials from the interaction of a single metal atom with perfect one-layer graphene has been considered for the first time. Numerical calculations have been performed for different heteroatomic pairs. The potential parameters were calculated from the equilibrium adsorption energy and distances in the adatom–graphene system and the data of numerical calculations performed by the density functional theory method. The Levenberg–Marquardt algorithm was used for optimization. The calculations are consistent with available literature data on melting points of metal carbides and ionic and covalent radii. The results obtained are of significant practical interest since they open up a new opportunity for evaluating the parameters of pairwise potentials. The advantage of the method is that the empirical combining rules are not used to calculate the parameters of potentials.

The open circuit voltage (VOC) deficit of Cu2ZnSn(S,Se)4 (CZTSSe) kesterite solar cells is higher than that of the closely related Cu(InGa)Se2 solar cells. One of the most promising strategies to overcome the large VOC deficit of kesterite solar cells is by reducing the recombination losses through appropriate cation substitution. In fact, replacing totally or partially Zn or Cu by an element with larger covalent radius one can significantly reduce the concentration of I–II antisite defects in the bulk. In this study, an investigation of the impact of partial substitution of Cu by Ag in CZTSSe solid solution monograins is presented. A detailed photoluminescence study is conducted on Ag-incorporated CZTSSe monograins and a radiative recombination model is proposed. The composition and structural quality of the monograins in dependence of the added Ag amount are characterized using Energy Dispersive X-ray Spectroscopy and X-Ray Diffraction method, respectively. The Ag-incorporated CZTSSe monograin solar cells are characterized by temperature dependent current-voltage and electron beam induced current methods. It was found, that low Ag contents (x ≤ 0.02) in CZTSSe lead to higher solar cell device efficiencies.

Copper(I) and silver(I) pyrazolate complexes {[3,5-(3,5-(CF3)2Ph)2Pz]Cu}3 and {[3,5-(3,5-(CF3)2Ph)2Pz]Ag}3 have been synthesized using the fluorinated 3,5-(diaryl)pyrazole 3,5-(3,5-(CF3)2Ph)2PzH and copper(I) oxide and silver(I) oxide, respectively. The gold(I) analog was obtained from a reaction between Au(THT)Cl and [3,5-(3,5-(CF3)2Ph)2Pz]H/NaH. The X-ray crystal structures show that the coinage metal complexes {[3,5-(3,5-(CF3)2Ph)2Pz]M}3 (M = Cu, Ag, Au) are trinuclear in the solid state. They feature distorted nine-membered M3N6 metallacyclic cores. The M–N distances follow Cu < Au < Ag, which is the trend expected from covalent radii of the corresponding coinage metal ions. The 3,5-(3,5-(CF3)2Ph)2PzH forms hydrogen bonded trimers in the solid state that are further organized by π-stacking between aryl rings. Solid samples of {[3,5-(3,5-(CF3)2Ph)2Pz]M}3 display blue photoluminescence. The copper complex {[3,5-(3,5-(CF3)2Ph)2Pz]Cu}3 is an excellent catalyst for mediating azide–alkyne cycloaddition chemistry.

New ionic antimony complexes with a three-coordinated carbon atom in their cations, namely, [(Ph4SbO)3C]+[OSO2C6H3(NO2)2-2,4]– ⋅ 3PhH (32%) and [(p-Tol4SbO)3C]+Br– (traces), have been isolated when the products of reactions between pentaphenylantimony and 2,4-dinitrobenzenesulfonic acid and between penta(p-tolyl)antimony and hydrobromic acid were crystallized from a benzene–octane mixture in air along with the target products, such as tetraphenylantimony 2,4-dinitrobenzenesulfonate and tetra(p-tolyl)antimony bromide. The cations have nearly planar СO3Sb3 cores. The ОСО and COSb angles are close to 120°, whereas the C–O bonds vary within 1.277(4)–1.290(3) A, and the Sb–O distances (2.266(2)–2.299(2) A) exceed the sum of the covalent radii of antimony and oxygen atoms. It has been experimentally established that these complexes are formed as a result of interactions between the target products of the above-mentioned reactions with bis(tetraarylantimony) carbonates, which are also formed under the conditions of these reactions from pentaarylantimony and atmospheric carbon dioxide.

Boron atoms possess a short covalent radius and the flexibility to adopt sp2 hybridization, which favour the formation of diverse two-dimensional allotropes of boron. Several examples of such boron sheets with metallic nature have been reported recently. However, a semiconducting boron crystal with a direct bandgap is rarely reported either in bulk boron crystals or in two-dimensional boron sheets. Here, the boron sheets with a direct bandgap are synthesized on a Ni foil substrate by chemical vapor deposition. The boron sheets with 48 boron atoms per unit cell have a quasicubic structure, and they are semiconducting and have a direct bandgap of around 2.4 eV, which are verified by combining theoretical and experimental investigations. The result greatly expands the known allotropy of the fifth element and opens vast opportunities to design 2D boron sheets with tunable optical, electronic, magnetic and chemical properties.

Single-atom catalysts (SACs) introduce as a promising category of electrocatalysts, especially in the water-splitting process. Recent studies have exhibited that nitrogen-doped carbon-based SACs can act as a great HER electrocatalyst. In this regard, Adaptive Neuro-Fuzzy Inference optimized by Gray Wolf Optimization (GWO) method was used to predict hydrogen adsorption energy (ΔG) obtained from density functional theory (DFT) for single transition-metal atoms including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au embedded in N-doped carbon of different sizes. Various descriptors such as the covalent radius, Zunger radius of the atomic d-orbital, the formation energy of the single-atom site, ionization energy, electronegativity, the d-band center from − 6 to 6 eV, number of valence electrons, Bader charge, number of occupied d states from 0 to − 2 eV, and number of unoccupied d states from 0 to 2 eV were chosen as input parameters based on sensitivity analysis. The R-squared and MSE of the developed model were 0.967 and 0.029, respectively, confirming its great accuracy in determining hydrogen adsorption energy of metal/NC electrocatalysts.

A theoretical approach used in the work—the theory of generalized charges—is an asymptotic approximation of quantum mechanics for interatomic forces. To some extent it is similar to the Thomas–Fermi model of inhomogeneous electron gas. The well-known consequence of Teller's theorem about the impossibility of applying the Thomas–Fermi model to interatomic forces is circumvented by replacing the electric field with the field of generalized charges. To clarify the origin of generalized charges, the concept of covalent bond function is introduced through the overlap integral of the electronic wave functions of interacting atoms. The proposed approach is convenient to explain two types of interatomic interactions (covalent and van der Waals) and to derive the expressions for their energies. It is shown that the covalent bond function is involved in the electronic balance and associated with generalized charges and wave vectors of electrons. New analytical relationships, restrictions and regularities for the length and potential of a homopolar covalent bond are deduced. In particular, expressions are obtained for the covalent radii and bond distances of homonuclear molecules in the ground state. The theory of generalized charges also has excellent prospects for describing the binding energy, which will be shown independently.

In this manuscript, three examples retrieved from the PDB are selected to demonstrate the existence and relevance of spodium bonding (SpB) in biological systems. SpB is defined as an attractive noncovalent interaction between elements of group 12 of the periodic table acting as a Lewis acid and any atom or group of atoms acting as an electron donor. The utilization of this term (SpB) is convenient to differentiate classical coordination bonds from noncovalent interactions. In the latter, the distance between the electron rich and the spodium atoms is longer than the sum of the covalent radii but shorter than the sum of the van der Waals radii. In most Zn-dependent metalloenzymes, the spodium atom is bonded to three imidazole moieties belonging to the side chains of histidine amino-acids. Herein, in addition to the investigation of the SpB in the active site of three exemplifying enzymes, theoretical models where the Zn(II) atom is bonded either to three imidazole or triazole ligands are used in order to investigate the strength of the SpB and its competition with hydrogen bonding. A series of Lewis bases and anions have been used as SpB acceptors combined with six SpB donors (receptors) of general formula [ZnY3X]+ (Y = imidazole and triazole and X = Cl, N3 and SCH3). In addition to the investigation of the energetic and geometric features of the complexes, the SpB interactions have been further characterized using the natural bond orbital (NBO) method, quantum theory of “atoms-in-molecules” and the noncovalent interaction plot (NCI plot).

Sila-molecules have recently attracted attention due to their promising applications in medical and industrial fields. Compared with all-carbon parent compounds, the different covalent radius and electronegativity of silicon from carbon generally endow the corresponding sila-analogs with unique biological activity and physicochemical properties. Vinylsilanes feature both silyl-hyperconjugation effect and versatile reactivities, developing vinylsilane-based Smiles rearrangement will therefore provide an efficient platform to assemble complex silacycles. Here we report a practical Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides for delivering naphthyl-fused benzosiloles under visible-light photoredox conditions. The combination of experiments and density functional theory (DFT) energy profiles reveals the reaction mechanism involving α-silyl radical Smiles rearrangement., Arene-fused siloles have attracted interest due to their promising applications in electronic and optoelectronic devices. Here, the authors report Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides via α-silyl radical Smiles rearrangement for accessing naphthyl-fused benzosiloles under visible-light photoredox conditions.

We have performed density functional theory calculations to study the binding and charge transfer at interfaces between blue phosphorene and various metal substrates. The substrates considered are Al(111), Ag(111), Au(111), Pt(111), Zr(0001) and Sc(0001). The substrates suitable for use for synthesis and exfoliation of blue phosphorene, or instead for use as electrodes for either making contacts or charge doping blue phosphorene, are identified. We find that both the charge transfer and strength of binding correlate excellently with a simple descriptor D = Δ χ / Δ R , where Δχ is the difference in Pauling electronegativities between the metal and phosphorus, and Δ R the corresponding difference in covalent radii. The predictions of the descriptor are validated by subsequent calculations on Pd(111), Cu(111) and Ir(111) substrates. This easily computed descriptor should help in the rapid identification of two-dimensional material + metal combinations suitable for specific applications.

The mechanical properties of Czochralski (Cz) silicon wafers dictate fundamental limits on the fabrication of diverse electronic devices. Certain impurities with sufficiently high concentrations may affect the mechanical properties of Cz silicon. The underlying mechanisms for such influences have been being explored in the past decades. In this work, the effects of antimony (Sb)- and tin (Sn)-doping at 1018 cm−3 level on the mechanical properties of Czochralski (Cz) silicon have been comparatively investigated. Since Sb and Sn have quite close tetrahedral covalent radii in silicon, the lattice strains resulted from Sb- and Sn-doping and their consequent effects on the mechanical properties of silicon are approximately identical. In silicon, Sb is an electrically active impurity while Sn is a neutral one. Therefore, the present work can essentially reveal the role of electrical activity of Sb playing in the mechanical properties of Cz silicon. It is found that Sb-doped Cz (Sb-Cz) silicon possesses a slightly higher hardness than Sn-doped Cz (Sn-Cz) silicon. Moreover, the dislocation gliding at 500 or 600 °C in Sb-Cz silicon requires a much larger critical resolved shear stress than that in Sn-Cz silicon. At such two temperatures, Sb-Cz silicon remains to be n-type in electrical conduction. The aforementioned two results are believed to be ascribed to the resistance of dislocation motion by the Coulomb interaction between the positively charged Sb ions and the dislocations that are deep-level acceptors thus being negatively charged in Sb-Cz silicon. As the temperature is increased to 700 °C and above, the dislocation gliding in Sb-Cz silicon is not substantially different from that in Sn-Cz silicon. At such elevated temperatures, Sb-Cz silicon becomes intrinsic in electrical conduction like Sn-Cz silicon. In this context, there is no Coulomb interaction between Sb ions and dislocations anymore to impede the dislocation gliding in Sb-Cz silicon. In addition, it is found that the indentation fracture toughness of Sb-Cz is almost the same as that of Sn-Cz silicon. Actually, the fracture of silicon is essentially a cleavage process, to which the electrical activity of Sb is irrelevant.

The reactions of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzimMe), towards the zinc and cadmium halides, MX2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzimMe)]2MX2, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N–H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzimMe)]2ZnX2 and [H(sebenzimMe)]2CdX2 (X = Cl, Br), exhibit two intramolecular N–H⋯X interactions, whereas the iodide derivatives, [H(sebenzimMe)]2ZnI2 and [H(sebenzimMe)]2CdI2, exhibit only one intramolecular N–H⋯I interaction. Comparison of the M–Se and M–Cl bond lengths of the chloride series, [H(sebenzimMe)]2MCl2 (M = Zn, Cd, Hg), indicates that while the average M–Cl bond lengths progressively increase as the metal becomes heavier, the variation in M–Se bond length exhibits a non-monotonic trend, with the Cd–Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzimMe)]2CdCl2, [H(sebenzimMe)]3CdCl2·[H(sebenzimMe)]4CdCl2, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI2 and H(sebenzimMe) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzimMe)][H(benzimMe)]CdI2, a transformation that is associated with cleavage of the C–Se bond.

One of the reaction products of triphenylantimony dichloride and triphenylantimony bis (2,4-dibromophenoxide) (1:1 mol.) in benzene in air is the compound of three-coordinated carbon [Ph 3 Sb(Cl)O] 3 C × PhH ( 1 ). The compound has been identified by IR spectroscopy and X-ray diffraction analysis. According to the X-ray diffraction analysis the target product is a benzene solvate [С 61 H 51 Cl 3 O 3 Sb 3 , М = 1303.65; the monoclinic system, space group P2 1 /c; a 17.17(2), b 18.75(2); c 17.322(18) A; α 90.00, β 90.58(5), γ 90.00 град.; V 5576(11) A 3 ; Z 4; µ 1.630 mm –1 ; F (000) 2580.0; crystal size 0.28 × 0.22 × 0.11 mm; 2θ for data collection 6.4 - 36.8 degrees; index ranges −15 ≤ h ≤ 15, −16 ≤ k ≤ 16, −15 ≤ l ≤ 15; total reflections 24392; independent reflections 3981; R int 0.0516; variables 632, GOOF 1.141; R 1 = 0.0392; wR 2 = 0.0912; residual electron density 0.43/–0.35 e/A 3 ]. The COSb angles in the compound 1 vary in the interval 123.3(8)-127.1(8)°. The C–O shortened distances (1.365(15)–1.385(15) A) compared to the sum of the covalent radii of carbon and oxygen atoms (1.51 A) indicate an increase in the multiplicity of these bonds. The abnormal reduction of Sb–O distances (1.986(7), 2.001(7), 2.011(7) A) in the neutral molecule 1 compared to the sum of the covalent radii of antimony and oxygen atoms (2.14 A) implies delocalization of the electron density in the CO 3 Sb 3 core. The Sb – Cl distances are slightly longer than the sum of the covalent radii of antimony and chlorine atoms and are longer than ones in triphenylantimony dichloride. The antimony atoms have a distorted trigonal-bipyramidal coordination with heteroatoms in axial positions. The formation of the crystal structure is due to the formation of weak hydrogen bonds such as С···Н (2.72-2.90 A) and Сl···Н (2.94 A). Complete tables of coordinates of atoms, bond lengths and valence angles are deposited at the Cambridge Structural Data Bank (No. 1851485; deposit@ccdc.cam.ac.uk; http:// www.ccdc.cam.ac.uk/data_request/cif).

We report here the synthesis of two new PbIJII) compounds in which the lead center is coordinated by organic ligands via S and O donor atoms. Remarkably, in both compounds the Pb coordination is hemidirectional, which facilitates the approach of extra donors to establish interactions at longer distances. Such interactions are of σ-hole nature between the Pb and O/S atoms, acting as Lewis acid and bases, respectively. Interestingly, the Pb⋯S/O distances are closer to the sum of the covalent radii than to the van der Waals ones, which suggests a considerably strong interaction. We have performed a structural analysis of the crystal structures as well as a theoretical analysis based on DFT calculations to gain deeper insight into the origin and features of these σ-hole interactions. Moreover, the nature of the Pb⋯S/O interactions have been further analysed by means of AIM, MEP and NBO calculations.

Complexes Ph3(C2H4O2)Sb⋅⋅⋅DMSO (I), (3-FC6H4)3(C2H4O2)Sb⋅⋅⋅DMSO (II), and (4‑MeC6H4)3-(C6H4O2)Sb⋅⋅⋅DMSO (III) are synthesized by the reactions of triarylantimony with ethylene glycol or pyrocatechol in the presence of an oxidant and dimethyl sulfoxide (DMSO). According to the X-ray diffraction analysis data, the Sb atoms in the complexes have the coordination of a distorted octahedron with the chelate cycle (C2H4O2 or C6H4O2) and two aryl groups in the equatorial plane, and the third aryl group and DMSO molecule occupy the axial positions. The СSbO axial angles are 173.59(5)° (I); 175.96(8)°, 175.93(8)° (II); and 174.07(8)° (III). The Sb⋅⋅⋅О=SMe2 distances (2.346(2)−2.407(2) A) considerably exceed the sum of covalent radii of the atoms.

Metal–metal multiple bonding is common amongst the d-block transition metals; but intermetallic multiple bonding involving f-block metals, such as uranium, is extremely rare. This is largely due to the difficulties in synthesis and characterization of the relevant compounds. Here, we report a set of heterometallic clusters featuring uranium-metal triple bond s. X-ray diffraction reveals that the uranium-iron (1.9689(13) A) and uranium-cobalt (2.0926(7) A) bond lengths are shorter than the sum of the triple bond covalent radii for corresponding atoms. These complexes represent the first structurally authenticated example of multiple bonding between f-block elements and first-row transition metals. Theoretical studies reveal the high bond orders ( up to 2.93 ) and the significant degree of covalency in these uranium-metal triple bonds. These studies demonstrate that the uranium-metal multiple bonds are no longer an elusive bonding motif, and this opens an avenue to investigation of the potential applications in catalysis and small-molecule activation of heterometallic clusters with actinide-metal multiple bonds .

Thermodynamics must be favorable for the growth of carbon nanotubes (CNTs) and graphene to take place, but a kinetic study is required to find the operating mechanism. In fact, thermodynamics indicates whether a reaction is possible; however, the route prevailing is not necessarily the most thermodynamically favorable, but the fastest one. Detailed kinetic studies state that there are three alternative routes operating under different temperature and pressure rates. The modes and rates of diffusion of carbon (C) atoms and noble metals have been known since the 1930s, but proof of C bulk diffusion operating in CNT growth came from detailed kinetic studies performed in the early 1970s, when reversible versus irreversible C formation was discussed with examples. The reason for interstitial C bulk diffusion in transition metals is evidenced based on the values of covalent radius. The reason for operating under steady-state conditions (linearity of the weight versus time) when searching for the operating mechanism is discussed herein. The steady-state C formation process operates sometimes with two different solid phases at each side of the catalyst particle (e.g., Ni and Ni3C), with thicknesses proportional to 1/D of the respective C bulk diffusivities when the carbon bulk diffusion step is the rate-determining one.

International audience; Models of protein chains containing a seleno-cysteine (Sec) residue have been investigated by gas phase laser spectroscopy in order to document the effect of the H-bonding properties of the SeH group in the folding of the Sec side chain, by comparison with recent data on Ser- and Cys-containing sequences. Experimental data, complemented by quantum chemistry calculations and natural bonding orbital (NBO) analyses, are interpreted in terms of the formation of a so-called 5g intra-residue motif, which bridges the acceptor chalcogen atom of the side chain to the NH bond of the same residue. This local structure, in which the O/S/Se atom is close to the plane of the N-terminal side amide, is constrained by local backbone-side chain hyperconjugation effects involving the S and Se atoms. Theoretical investigations of the Cys/Sec side chain show that (i) this 5g motif is an intrinsic feature of these residues, (ii) the corresponding H-bond is strongly non-linear and intrinsically weak, (iii) but enhanced byg- and b-turn secondary structures, which promote a more favorable 5g H-bonding approach and distance. The resulting H-bonds are slightly stronger in selenocysteine than in cysteine, but nearly inexistent in serine, whose side chain in contrast behaves as a H-bonding donor. The modest spectral shifts of the Cys/Sec NH stretches measured experimentally reflect the moderate strength of the 5g H-bonding, in agreement with the correlation obtained with a NBO-based H-bond strength indicator.The evolution along the Ser, Cys and Sec series emphasizes the compromise between the several factors that control the H-bonding in a hyperconjugation-constrained geometry, among them the chalcogen van der Waals and covalent radii. It also illustrates the 5g H-bond enhancements with the Sec and Cys residues favoured by the constraints imposed by the g- and b-turn structures of the peptide chain

Highly-mismatched III-V semiconductor alloys containing dilute concentrations of bismuth (Bi) have attracted significant attention in recent years since their unique electronic properties open up a range of possibilities for practical applications in semiconductor lasers, photovoltaics, spintronics, photodiodes, and thermoelectrics. Research on dilute bismide alloys has primarily focused to date on $\text{GaAs}_{1-x}\text{Bi}_{x}$ , where incorporation of Bi brings about a strong reduction of the direct $\Gamma$ -point band gap ( $E_{g}{}^{\Gamma}$ ) –by up to 90 meV per % Bi at low Bi compositions $x$ –characterised by strong, composition-dependent bowing. This unusual behaviour derives from the large differences in size (covalent radius) and chemical properties (electronegativity) between As and Bi.Bi, being significantly larger and more electropositive than As, acts as an isovalent impurity which primarily impacts and strongly perturbs the valence band (VB) structure. This is in contrast to dilute nitride alloys, in which small electronegative nitrogen (N) atoms strongly perturb the conduction band (CB) structure in $\text{GaN}_{x}\text{As}_{1-x}$ and related alloys. Additionally, Bi, being the largest stable group-V element, has strong relativistic (spin-orbit coupling) effects. As such, the reduction of $E_{g}{}^{\Gamma}$ in $(\text{In})\text{GaAs}_{1-x}\text{Bi}_{x}$ is accompanied by a strong increase in the VB spin-orbit splitting energy ( $\Delta_{\text{SO}}$ ).

On the basis of the first structurally authenticated LArU–FeCp(CO)2 (LAr = deprotonated p-terphenyl bis(aniline) ligand) complex bearing an unsupported U–Fe bond, we expanded the structures of comp...

Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN- and XCN- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F- , and SeCN- , the complex [1 a-F]- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C6 F4 Hg)3 , which was characterized by XRD.

Impurities are often driven to segregate to grain boundaries, which can significantly alter a material's thermal stability and mechanical behavior. To provide a comprehensive picture of this issue, the influence of a wide variety of common nonmetallic impurities (H, B, C, N, O, Si, P and S) incorporated during service or materials processing are studied using first-principles simulations, with a focus on identifying changes to the energetics and mechanical strength of a Cu Σ5 (310) grain boundary. Changes to the grain boundary energy are found to be closely correlated with the covalent radii of the impurities and the volumetric deformations of polyhedra at the interface. The strengthening energies of each impurity are evaluated as a function of covalent radius and electronegativity, followed by first-principles-based tensile tests on selected impurities. The strengthening of a B-doped grain boundary comes from an enhancement of the charge density among the adjacent Cu atoms, which improves the connection between the two grains. Alternatively, the detrimental effect of O results from the reduction of interactions between the Cu atoms. This work deepens the understanding of the possible beneficial and harmful effects of impurities on grain boundaries, providing a guide for materials processing studies.

Four new Pb(II) complexes of nicotinoylhydrazone and picolinoylhydrazone-based ligands and three different anionic co-ligands (acetate, thiocyanate and iodide) have been synthesized and characterized by structural, analytical and spectroscopic methods. The ligands coordinate to the Pb(II) metal center in a tridentate fashion via two nitrogen and one oxygen donor atoms either in mono-deprotonated or in neutral forms. Single-crystal X-ray crystallography reveals that the molecular complexes aggregate into larger entities depending upon the anion coordinated to the metal centre. The Pb(II) center is hemidirectionally coordinated and, consequently, it is sterically ideal for establishing tetrel bonding interactions. Consequently, in the crystal structures of all the complexes, the Pb participates in short contacts with nitrogen, iodide or sulphur atoms. These contacts are shorter than the sums of the van der Waals radii and larger than the sums of the covalent radii, therefore they can be defined as non-covalent tetrel bonding interactions. They interconnect the covalently bonded units (monomers or dimers) into supramolecular assemblies (1D infinite chains and 3D structures). Hirshfeld surface analysis and fingerprint plots have been used to analyse the contribution of contacts involving the Pb atom. We have analysed the interesting supramolecular assemblies observed in the solid state of all four complexes by means of DFT calculations and characterized them using Bader's theory of atoms-in-molecules.

Ionocovalency theory is defined “…everything exists in ionocovalency, the harmony of ionic energy with the covalent environment.” The authors have succeeded in thoroughly studying ionic energy part of the ionocovalent theory, and will now focus target on the covalent environment part of the theory. The essence of chemical reactions and chemical bonds is the overlap of atomic orbitals, the electron density or the ionocovalent potential. The covalent radius rc is the unique parameter that can be considered as an atomic property derived from molecules for data reduction and can be assigned to the atoms interacting in molecules. In the present study, A new application view of covalent radii of multidimensional world is revealed by the ionocovalency theory which can quantitatively describe the chemical phenomena and qualitatively correlates to the universal observations.

The hexagonal boron-noble gas compounds B 6 Ng n 4+ (n = 1–6, Ng = He Rn) have been studied theoretically. The geometry, bond energies and thermodynamics properties are reported. For Ar Rn, the B Ng bond length is close to the sum of the covalent radii of B and Ng, the B Ng average bond energy is large up to 59.61–169.43 kcal/mol. There is large charge transfer from Ng to the boron ring, the Ng → boron σ-donation originating from the interaction between the valence p orbital of Ng and the LUMO of the boron ring is the predominant contribution towards the Ng B bond stabilization. The NICS analysis shows that B 6 Ng n 4+ have aromaticity.

It is demonstrated that the effective atomic radii suitable for identification of covalent bonding can be revealed from the parameters of machine-learning classifier trained to distinguish between bonded and non-bonded pairs of atoms in 28 710 molecules. The proposed way cardinally differs from the conventional technique of finding the atomic radii by solving a regression problem and approximating the bond lengths by the sum of adjustable parameters. Despite the contrasting approach, the proposed 'machine-learned atomic radii' obtained for H, B, C, N, O, F, Si, P, S, Cl, Ge, As, Se, Br elements are shown to be in close agreement with the conventional 'regression-based' covalent radii. We find this example appealing in demonstrating how some of the concepts peculiar to chemical intuition can be re-discovered by using a suitable machine-learning model. The boundaries between ‘definitely bonded’ and ‘likely bonded’ interatomic distances introduced naturally in the proposed formulation may prove useful for molecular modeling software.

A new series of isostructural rare earth compounds R1+xZr1−xNi (R = Er, Tm, Lu; x ~ 0.5) was synthesized from the elements by arc melting and subsequent annealing at 870 K for 1400 h. The crystal structures of the intermetallic compounds were investigated by means of single-crystal X-ray diffraction. They all crystallize in the TiNiSi structure type (space group Pnma, No. 62, oP12). In R1+xZr1−xNi, the R/Zr statistical mixture leading to nonequiatomic compositions occupies the position corresponding to the nickel site of the TiNiSi structure type. The calculated shortest interatomic distances are close to the sums of the single-bond covalent radii of respective elements. Electronic structure calculations performed with the tight-binding LMTO method revealed the non-zero density of states at the Fermi level and suggest metallic character. R1+xZr1−xNi (R = Er, Tm, Lu; x ~ 0.5) undergoes no long-range magnetic ordering down to 2 K.

The circular cationic compounds B3Rg n +(n=1—3, Rg=He—Rn) formed by the electron-deficient aromatic ion B3+ trapping rare gases were studied theoretically. The formed B—Rg bond has large bonding energy in the range of 60—209 kJ/mol, its length is close to the sum of covalent radii of B and Rg, for Ar—Rn. The analyses based on the natural bond orbitals and electron density topology show that the B—Rg bonds for Ar—Rn have strong covalent character. The geometric structures, binding energy, bond nature and thermodynamic stability of the boron-rare gas compounds show that these species for Ar—Rn may be experimentally available. Several different theoretical studies have demonstrated that these triangular cations are aromatic.

Bis(4-bromophenoxy)tris(para-tolyl)antimony (I), bis(4-nitrophenoxy)tris(para-tolyl)antimony (II), bis(4-nitrophenoxy)tris(4-fluorophenyl)antimony (III), bis(2,3,4,5,6-pentafluorophenoxy)tris(4-fluorophenyl) antimony (IV), and bis(2,3,4,5,6-pentachlorophenoxy)tris(4-fluorophenyl)antimony (V) (CIF files CCDC 1470829 (I), 1474589 (II), 1062337 (III), 1470476 (IV), and 1472954 (V)) are synthesized in high yields by the reactions of tris(para-tolyl)- and tris(4-fluorophenyl)antimony with 4-bromo-, 4-nitro-, 2,3,4,5,6-pentafluoro-, and 2,3,4,5,6-pentachlorophenol, respectively, in diethyl ether in the presence of tert-butyl hydroperoxide. The Sb atoms in compounds I–V have a distorted trigonal bipyramidal coordination with the aroxy groups in the axial positions (angles OSbO 174.08(11)°–179.4(5)°). The average Sb–C bond lengths in compounds I–V are similar and independent of the nature of the para-substituent in the aryl rings. The Sb–O distances are close to the sum of covalent radii of Sb and O atoms. Hydrogen bonds H···F are involved in the formation of the crystal structures of compounds III–V.