Competition between hydrogen bond and σ-hole interaction in SCS-HArF and SeCSe-HArF complexes

A computational study of the complexes formed between HArF and XCX (X?=?O, S, and Se) has been performed at the MP2/aug-cc-pVTZ level. Two types of complexes were found. One is formed through a hydrogen bond with XCX as the electron donor and the other is formed through the σ-hole interaction with XCX as the electron acceptor. The OCO-FArH complex is more stable than the OCO-HArF complex, whereas the XCX-HArF (X?=?S and Se) complex is more stable than the XCX-FArH complex. The distant H-Ar bond is shortened and exhibits a blue shift, but the associated one displays a red shift in SCS-HArF and SeCSe-HArF complexes. When compared with XCX-HF complex, the structure of the complex suffers a great effect from the inserted noble gas atom. The natural bond orbital (NBO) and atoms in molecules (AIM) have been performed for a better understanding of the interactions.     

On difference of properties between organic fluorine hydrogen bond C–H···F–C and conventional hydrogen bond

The existence of C–H···F–C hydrogen bonds in the complexes of trifluoromethane and cyclic molecule (oxirane, cyclobutanone, dioxane, and pyridine) has been experimentally proven by Caminati and co-workers. This study presents a theoretical investigation on these C–H···F–C hydrogen bonds at B97D/6-311++G^** and MP2/6-311++G^** levels, in terms of C–H vibrational frequency shifts, atoms in molecules characteristics, and the bonding feature of C–H···F–C hydrogen bonds. It is found that in three important aspects, there are significant differences in properties between C–H···F–C and conventional hydrogen bonds. The C–H···F–C hydrogen bonds show a blueshift in the C–H vibrational frequencies, instead of the X–H normal redshift in X–H···Y conventional hydrogen bonds. The natural bond orbital (NBO) analyses show that σ and p types of lone pair orbitals of the F atom to an antibonding σ^*_H–C orbital form a dual C–H···F–C hydrogen bond. Such a dual hydrogen bonding leads to the proton acceptor directionality of the C–H···F–C hydrogen bond softer. Our studies also show that the Laplacian of the electron density (▽²ρ_BCP) is not always a good criterion for hydrogen bonds. Therefore, we should not recommend the use of the Laplacian of the electron density as a criterion for C–H···F–C hydrogen bonds.     

The strong OHO hydrogen bond. How much covalency?

In the strong OHO hydrogen bond of the phosphoric acid–urea 1?:?1 complex the proton shifts gradually with temperature from the donor towards the acceptor atom, passing through the center of the hydrogen bond at around 315?K. The AIM parameters were evaluated for the published neutron structures at different temperatures. The values of the electron density, its Laplacian, and the energy densities at both the critical points between the proton and the oxygen atoms in the OHO hydrogen bond were correlated with the OH and HO distances. Changes in the AIM parameters of the strong hydrogen bond were compared with those of the weak NHO bond in this complex.     

A first-principles investigation into the hydrogen bond interaction in β-HMX

A theoretical study of structural and electronic properties of β-HMX crystal is performed using density-functional theory(DFT). The total density of states(TDOS) is presented. The atomic orbit projected density of state(PDOS) from the p-type orbit of C,N,O and the s-type orbit of H is discussed. The study by analyzing the PDOS shows that the structure of β-HMX crystal possesses C-H···O intra- and inter-molecular hydrogen-bonding. There exists a hydrogen bonding between H5 -1s and O12 -2p orbits,between H19 -1s and O28 -2p orbits of intra molecules,and between H19 -1s and O24 -2p orbits of inter molecules. The Mulliken population analysis is also made.     

Electron density characteristics and charge transfer effect of hydrogen bond O–H···Pt(II): atoms in molecules study and natural bond orbital analysis

In this report, we extended the works of Rizzato et al. [Angew. Chem. Int. Ed. 49, 7440 (2010)] on the nature of O–H···Pt hydrogen bond in trans-[PtCl₂(NH₃)(N–glycine)]·H₂O(1·H₂O) complex, by computational study of O–H···Pt interaction in [NBu₄][Pt(C₆F₅)₃(8-hydroxyquinaldine)], with emphasis on charge transfer effect in this interaction of platinum(II) and hydrogen atom. According to the crystallographic geometry reported by José María Casas et al., [NBu₄][Pt(C₆F₅)₃(8-hydroxyquinaldine)] possesses one O–H···Pt hydrogen bridging interaction, similar to the case in trans-[PtCl₂(NH₃)(N–glycine)]·H₂O(1·H₂O) complex. On the basis of topological criteria of electron density, we characterised this O–H···Pt interaction. Charge transferred between platinum(II) and σ^*_O–H orbital in this complex was calculated by using NBO method. The stabilised energy associated to charge transfer was estimated using a direct proportionality, that is 2–3 eV per electron transferred. Charge transfer effects in O–H···Pt hydrogen bonds were studied for these two complexes. Our results indicate that the interaction of O–H···Pt is closed–shell in nature with significant charge transfer, and that charge transfer effect is not negligible in the interaction of O–H···Pt. The second conclusion is different from the result of Rizzato et al.     

Can 2‐acylpyrroles form an intramolecular hydrogen bond?

The formation of intramolecular hydrogen bonding by certain N‐substituted 2‐acylpyrroles has been demonstrated by B3LYP/aug‐cc‐pVDZ calculations, the quantum theory of atoms in molecules, and the natural bond orbital method. Total electron energy densities H_BCP at the bond critical point of the H?O bond were applied to analyze the strength of these interactions. The relations between quantum theory of atoms in molecules, carbonyl stretching vibrational modes ν_{C = O}, and natural bond orbital parameters associated with the formation of the C–H?O interaction have been established. The short contacts were found experimentally in the crystal structure of a new 2‐acylpyrrole derivative 5‐chloro‐2‐oxopentyl‐1‐(5‐chloro‐2‐oxopentyl)pyrrolo‐2‐carboxylate. The influence of 2‐ and N‐substitution of 2‐acylpyrroles on C‐H?O interaction energy is discussed. It was found that the methylene group may act as a proton donor leading to a red‐shift or blue‐shift phenomenon of the ν_C–H stretching mode. Copyright © 2015 John Wiley & Sons, Ltd.     

On the role of a weak hydrogen bond OH…O in the formation of the anomalous dielectric response of crystals and polymers near 40°C

In some crystals, polymers, and gels that contain hydrogen bonds OH…O, NH…O of length 2.8–3 Å or water molecules, gigantic anomaly of dielectric permittivity (? ～ 10³–10⁶) is observed in certain circumstances at frequencies of 1–10⁶ Hz, which is accompanied by peculiarities in conductivity σ and dielectric losses tanδ. In crystals this effect appears after a sudden cooling to ?50°C and it is observed at slow heating in the range of 20–40°C. At the return temperature course from 40°C dependences ?(T), σ(T), and tanδ(T) have their usual values. Anomalies in objects that differ by their compositions are unified by their temperatures, which are all close to 40°C. Authors have made an attempt to explain the similarity of these phenomena by the features of hydrogen bonds that are present in the objects.     

Structural phase states and properties of the layer surfaced on low-carbon steel with Fe‒C‒Cr‒Nb‒W powder-core wire followed by electron-beam processing

Structural phase states and tribological properties of the coating surfaced onto Hardox 450 martensite low-carbon steel with powder wire Fe?C?Cr?Nb?W and modified by subsequent electron-beam processing are studied by methods of modern physical material science. It is shown that irradiation of ~5 thick surfaced layer with high intensity pulsed electron beams results in the formation of ~20 μm thick surface layer with the master phases of α-Fe and NbC, Fe₃C and M₆C(Fe₃W₃C) carbides. The main difference of the surface layer modified with electron-beam processing from the unmodified volume of the surfacing is the morphology and dimensions of the second phase inclusions. In the modified layer of the surfacing the inclusions have smaller dimensions and are located in the form of interlayers along the grain boundaries. In unmodified surfacing the particles of the faceted shape located chaotically in the grain volume are the basic morphological type of the inclusions. It is noted that the small value of crystal lattice Nb parameter observed in the experiment may be caused by the high level of vacant interstitial sites having the smaller size in comparison with the occupied interstitial sites. It is established that wear resistance of the surfaced layer after electron-beam processing increases more than 70-fold relative to wear resistance of Hardox 450 steel and friction coefficient decreases significantly (~3-fold).     

How universal are hydrogen bond correlations? A density functional study of intramolecular hydrogen bonding in low-energy conformers of α-amino acids

Hydrogen bonding is one of the most important and ubiquitous interactions present in Nature. Several studies have attempted to characterise and understand the nature of this very basic interaction. These include both experimental and theoretical investigations of different types of chemical compounds, as well as systems subjected to high pressure. The O–H..O bond is of course the best studied hydrogen bond, and most studies have concentrated on intermolecular hydrogen bonding in solids and liquids. In this paper, we analyse and characterise normal hydrogen bonding of the general type, D–H...A, in intramolecular hydrogen bonding interactions. Using a first-principles density functional theory approach, we investigate low energy conformers of the twenty α-amino acids. Within these conformers, several different types of intramolecular hydrogen bonds are identified. The hydrogen bond within a given conformer occurs between two molecular groups, either both within the backbone itself, or one in the backbone and one in the side chain. In a few conformers, more than one (type of) hydrogen bond is seen to occur.

Interestingly, the strength of the hydrogen bonds in the amino acids spans quite a large range, from weak to strong. The signature of hydrogen bonding in these molecules, as reflected in their theoretical vibrational spectra, is analysed. With the new first-principles data from 51 hydrogen bonds, various parameters relating to the hydrogen bond, such as hydrogen bond length, hydrogen bond angle, bond length and vibrational frequencies are studied. Interestingly, the correlation between these parameters in these bonds is found to be in consonance with those obtained in earlier experimental studies of normal hydrogen bonds on vastly different systems. Our study provides some of the most detailed first-principles support, and the first involving vibrational frequencies, for the universality of hydrogen bond correlations in materials.     

Cooperative effects of hydrogen,halogen and beryllium bonds on model halogen-bonded FCl … YZ (YZ = BF,CO, N2) complexes in FX′ … FCl … YZ trimers (FX′ = FH,FCl, F2Be)

A computational study of model halogen-bonded FCl?…?YZ dimers and FX′?…?FCl?…?YZ (FX′ = FH, FCl, F₂Be; YZ = BF, CO, N₂) trimers was undertaken at the MP2/6-311++G (2d, 2p) level of theory. Three different trimer arrangements are possible and the cooperative effect of hydrogen-, halogen- and beryllium-bonding in each of these trimers was assessed relative to the FCl?…?YZ dimer. It was found that the beryllium bond has the largest cooperative effect, while the halogen bond has the smallest, with the hydrogen bond being intermediate between the other two interactions. Interesting trends in selected properties were identified and discussed.     

Antiproton–hydrogen and antihydrogen–hydrogen annihilation at sub‐Kelvin temperatures

The main properties of the interaction of ultra low‐energy antiprotons (E⩽10^-6 a.u.) and antihydrogen with atomic hydrogen are established. Elastic and inelastic cross‐sections and Protonium formation spectrum are calculated within quantum mechanical coupled channels approach. The results of calculations differ strongly from predictions made by extrapolation of semiclassical models to the energy domain of interest. It is shown that the main feature of the observables behaviour is determined by existence of a family of H, H near‐threshold metastable states. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Luminescent Properties of 1,4,5-Triphenylimidazole‒Phenothiazine Fluorophores

Two blue donor–acceptor fluorophores with 1,4,5-triphenylimidazole as the electron-transporting unit and phenothiazine as the hole-transporting unit were synthesized by grafting 1,4,5-triphenylimidazole moieties onto 3- and 3,7-position of the phenothiazine core and characterized by spectroscopic methods. Their thermal stability, photophysical, electrochemical and electroluminescence properties were systematically investigated. These compounds exhibit good thermal stability and show blue emission in dichloromethane solution and thin solid films. The solution-processed doped devices were fabricated by using these fluorophores as the emitting dopant in 1,3-bis(N-carbazolyl)benzene host, in which the device fabricated from the fluorophore containing two 1,4,5-triphenylimidazole moieties exhibited blue emission with a luminance of 648 cd/m² and external quantum efficiency of 1.48%.

     

Cooperative effects between tetrel bond and other σ–hole bond interactions: a comparative investigation

Covalently bonded atoms of Groups IV–VII tend to have anisotropic charge distributions, the electronic densities being less on the extensions of the bonds (σ–holes) than in the intervening regions. These σ–holes often give rise to positive electrostatic potentials through which the atom can interact attractively and highly directionally with negative sites. In this work, cooperative effects between tetrel bond and halogen/chalcogen/pnicogen bond interactions are studied in multi-component YH₃M···NCX···NH₃ complexes, where Y = F, CN; M = C, Si and X = Cl, SH and PH₂. These effects are analysed in detail in terms of the structural, energetic, charge-transfer and electron density properties of the complexes. The nature of the σ–hole bonds is unveiled by quantum theory of atoms in molecules and natural bond orbital theory. A favourable cooperativity is found with values that range between ?0.34 and ?1.15 kcal/mol. Many-body decomposition of interaction energies indicate that two-body energy term is the most important source of the attraction, which its contribution accounts for 87%–96% of the total interaction energy.     

The strengthening effect of a hydrogen or lithium bond on the Z···N aerogen bond (Z = Ar,Kr and Xe): a comparative study

An ab initio study is performed on O₃Z···NCM···NCX (Z = Ar, Kr and Xe; M = H and Li; X = H, F and CH₃) complexes to investigate cooperativity effects between aerogen and hydrogen or lithium bonding interactions in these systems. To understand the cooperative effects, a detailed analysis of the binding distances, interaction energies and bonding properties is performed on these complexes. The results indicate that all Z···N and H/Li···N binding distances in the ternary complexes are shorter than those of corresponding binary systems. For a given M or X, cooperative energies increase as Z = Xe > Kr > Ar. Moreover, O₃Z···NCLi···NCX complexes exhibit a larger cooperative energy than O₃Z···NCH···NCX ones. The non-covalent interaction (NCI) index analysis indicates that the formation of an H/Li···N interaction in the ternary complexes shifts the location of the spike associated with the Z···N interaction towards the negative λ₂ρ values. This indicates that NCI analysis can be regarded as a useful tool for the study of cooperative effects between two different non-covalent interactions. Also, cooperative effects in O₃Z···NCM···NCX complexes make a decrease in ¹⁴N nuclear quadrupole coupling constants of NCH or NCLi molecule.     

Effect of electron-donating and electron-withdrawing atoms on the C–H…Y hydrogen bond in model X3CH…YZ (X = B,F; YZ = BF,CO, N2) complexes

A computational study of model complexes X₃CH…YZ (X = B, F; YZ = BF, CO, N₂) was undertaken to assess the effect of electron-donating and electron-withdrawing X atoms on the properties of the C–H…Y hydrogen bond. Sequential substitution of the B atoms in B₃CH by F atoms to produce F₃CH allowed for the elucidation of interesting trends in the corresponding hydrogen-bonded complexes. The dipole moments and the dipole moment derivative with respect to C–H bond displacement for the proton donors and the chemical hardness of the Y atom of the proton acceptor YZ were found to be useful parameters for understanding these trends. It was found that a positive dipole derivative favours red-shifted hydrogen bonds, whereas a negative dipole derivative favours blue-shifted hydrogen bonds. However, decreasing hardness of Y (which correlates with increasing intermolecular attraction) modifies the interaction such that either greater C–H bond extensions/red shifts or smaller C–H bond compressions/blue shifts are obtained.     

Viscous detonation in H2‒O2‒Ar using intrinsic low-dimensional manifolds and wavelet adaptive multilevel representation

A standard ignition delay problem for a mixture of hydrogen-oxygen-argon in a shock tube is extended to the viscous regime and solved using the method of intrinsic low-dimensional manifolds (ILDM) coupled with a wavelet adaptive multilevel representation (WAMR) spatial discretization technique. An operator-splitting method is used to describe the reactions as a system of ordinary differential equations at each spatial point. The ILDM method is used to eliminate the stiffness associated with the chemistry by decoupling processes which evolve on fast and slow time scales. The fast time scale processes are systematically equilibrated, thereby reducing the dimension of the phase space required to describe the reactive system. The WAMR technique captures the detailed spatial structures automatically with a small number of basis functions thereby further reducing the number of variables required to describe the system. A maximum of only 300 collocation points and 15 scale levels yields results with striking resolution of fine-scale viscous and induction zones. Additionally, the resolution of physical diffusion processes minimizes the effects of potentially reaction-inducing artificial entropy layers associated with numerical diffusion.     

Scattering of protons and antiprotons by hydrogen atoms

The two-,four-,five-and fourteen-state approximations of the inpact parameter method have been applied to the excitation of hydrogen atoms by proton(p)and antiproton(p) impact.The effect of both channel and back couplings on the 2s and 2p excitations are investigated.The total cross sections are calculated for incident energies ranging from 1 to 2500keV.it is found that the effect of both channel and back couplings on the antiproton-induced reactions is greater than on that induced by protons.We compare the results with those of other theoretical and experimental works.     

Computational study of the cooperative effects between tetrel bond and halogen bond in XCN⋅⋅⋅F2CO⋅⋅⋅YCN complexes (X = H,F, Cl,Br; Y = F,Cl, Br)

ABSTRACT

Ab initio calculations have been accomplished to study the cooperativity between the halogen bond and tetrel bond in the XCN???F2CO???YCN (X = H, F, Cl, Br; Y = F, Cl, Br) complexes. F₂CO at the same time plays the role of Lewis acid with the π-hole on the C atom and Lewis base with the O atom to participate in the tetrel bond and in halogen bond, respectively. According to the geometry survey, the effect of a tetrel bond on a halogen bond is more pronounced than that of a halogen bond on a tetrel bond and the intermolecular distances in the triads are always smaller than the corresponding values in the dyads. In all cases, the halogen bond and tetrel bond in the termolecular complexes are stronger compared with those in the bimolecular complexes. So, from the intermolecular distances, interaction energies and many-body interactions demonstrate that there is positive cooperativity between the halogen bond and tetrel bond. The molecular electrostatic potential, atoms in molecules and natural bond orbital methodologies are used to analyse the nature of interactions of the complexes.     

A positron beam Doppler broadening analysis of formation and recovery of defects produced by ion irradiation in Fe‒C‒Cu alloys

Mechanisms of radiation embrittlement of reactor pressure vessel steels remain to be fully understood, particularly the nature of so-called ‘matrix defects’. One possible mechanism is vacancy cluster formation, probably assisted by cascade damage. In order to investigate the effect of copper on the formation and annealing processes of vacancy clusters, ion-irradiated Fe?C and Fe?C?Cu were investigated using a variable energy positron beam. Doppler broadening analysis revealed that vacancy-type defects are produced by ion irradiation and that copper addition reduces the open volume of the defects. Post irradiation annealing suggested the vacancy clusters do not have a substantial role in irradiation hardening.