The strengthening effect of a halogen,chalcogen or pnicogen bonding on halogen–π interaction: a comparative ab initio study

The aim of this work is to study the possible cooperative effects between Z···N and X···π interactions (Z = Cl, S, P and X = Cl, Br) in some model complexes, where both these interactions coexist. The nature of the interactions in these complexes is characterised by means of molecular electrostatic potential, electron localisation function, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. According to the results, the formation of an Z···N interaction in these systems makes a significant shortening of X···π distance. The cooperative enhancement of the X···π bonding in the ternary complexes depend on the strength of the Z···N interaction, and it becomes larger in the order Z = Cl > S > P. The mechanism of the cooperativity between the Z···N and X···π interactions is studied using the parameters derived from the QTAIM and NBO analyses.     

Strengthening of the halogen-bonding by an aerogen bond interaction: substitution and cooperative effects in O3Z···NCX···NCY (Z = Ar,Kr, Xe; X = Cl,Br, I; Y = H,F, OH) complexes

The geometry, interaction energy and bonding properties of ternary complexes O₃Z···NCX···NCY (Z= Ar, Kr, Xe; X = Cl, Br, I and Y = H, F, OH) are investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Two different types of intermolecular interactions are present in these complexes, namely, aerogen bond (Z···N) and halogen bond (X···N). The formation mechanism and bonding properties of these complexes are analysed with molecular electrostatic potentials, quantum theory of atoms in molecules and non-covalent interaction index. It is found that the cooperativity energies in the ternary complexes are all negative; that is, the interaction energy of the ternary complex is greater (more negative) than the sum of the interaction energies of the corresponding binary systems. Also, the cooperativity energies increase with the increase of the interaction energies. The cooperative effects in the ternary complexes make a decrease in the total spin–spin coupling constants across the aerogen bonding, J(Z–N), which can be regarded as a proof for the reinforce of Z···N interactions in the ternary complexes with respect to the binary systems.     

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.     

Theoretical study of cooperativity between hydrogen bond‒hydrogen bond,halogen bond‒halogen bond and hydrogen bond‒halogen bond in ternary FX…diazine…XF (X = H and Cl) complexes

ABSTRACT

In the present work, the cooperativity between hydrogen bond?hydrogen bond, halogen bond?halogen bond and hydrogen bond?halogen bond in ternary FX…diazine…XF (X = H and Cl) complexes is theoretically investigated. The sign of cooperative energy (E_coop) obtained in all of the triads is positive which indicates that the ternary complex is less stable than the sum of the two isolated binary complexes. Moreover, our calculations show that E_coop value in triads increases as FX…pyridazine…XF > FX…pyrimidine…XF > FX…pyrazine…XF. In agreement with energetic, geometrical and topological properties, electrostatic potentials and coupling constants across ¹⁵N…X?¹⁹F (X = ¹H or ³⁵Cl) hydrogen and halogen bonds indicate that hydrogen and halogen bonds are weakened in the considered complexes where two hydrogen and halogen bonds coexist. As compared to N…H hydrogen bond, it is also observed that cooperativity has greater effect on N…Cl halogen bond.     

The corona pressure effect (Δp) and the thermionic analogue of the Joshi effect (Δi)T in hydrogen in a semi-ionizer

Conditions favourable for the co-occurrence of the corona pressure effect and the thermionic analogue of the Joshi effect are determined and a study is made to find whether the corona pressure data can be used to interpret the mechanism of i.This consists of a part of the author's Ph. D. thesis accepted by the Banaras Hindu University in 1956–57.     

The effect of Ag adsorption on the structural,electronic, and optical properties of the ZnO(101̅0) surface: A first-principles study

The effect of the Ag adsorption on the structural, electronic and optical properties of the clean ZnO$(10\bar{1}0)$ surface was investigated using the first principles method. The obtained results show that adsorbed Ag atoms transfer charge to the surface which results in a charge accumulation in near-surface region accompanied with a decrease of the work function. On the other hand, our results show that the adsorption of Ag atoms leads also to the new optical absorption peaks in the visible region which could improve ZnO photocatalytical properties.     

Ab initio study of synergetic effects of two strong interactions of cation–π interaction and lithium bond in M+ ··· phenyl lithium ··· N (M = Li,Na, K; N = H2O and NH3) complex

Quantum chemical calculations have been performed to investigate the interplay between the cation–π interaction and lithium bonding in the M⁺?···?phenyl lithium?···?OH₂ and M⁺?···?phenyl lithium?···?NH₃ (M?=?Li, Na, K) complexes. The cation–π interaction and lithium bonding in the trimers become stronger relative to the dimers. The interaction energy of cation–π interaction is increased by about 4.4–6.3%, while that of lithium bonding is increased by about 5.2–15.9%. The cooperative energy becomes larger for the stronger cation–π interaction and lithium bond. The F atom and methyl group in the phenyl ring impose a reverse effect on the cation–π interaction and lithium bond. The interaction mechanism in the complexes has been understood with the many-body interaction analysis, electrostatic potentials, and energy decomposition.     

Enhancement effect of lithium bonding on the strength of pnicogen bonds: XH2P···NCLi···NCY as a working model (X = F,Cl; Y = H,F, Cl,CN)

MP2 calculations with aug-cc-pVDZ basis set were used to analyse intermolecular interactions in XH₂P···NCLi···NCY triads (X = F, Cl; Y = H, F, Cl, CN) which are connected via pnicogen bond and lithium bond. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries and interaction energies of dyads, and triads are investigated at the MP2/aug-cc-pVDZ computational level. Particular attention is paid to parameters such as cooperative energies and many-body interaction energies. All studied complexes, with the simultaneous presence of a lithium bond and a pnicogen bond, show cooperativity with energy values ranging between ?4.73 and ?8.88 kJ mol^?1. A linear correlation was found between the interaction energies and magnitude of the product of most positive and negative electrostatic potentials. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the title complexes.     

Ionization potentials and bond lengths for CO,N2, and F2 using the SCF-Xα-SW method: A study of the effect of overlapping spheres

Using a simple, arbitrary, but fixed procedure for the choice of sphere sizes in the overlapping sphere version of the SCF-Xα-SW method, results for the ionization potentials of CO, N₂, F₂, and H₂O are in considerably better agreement with experiment than those of the muffin-tin version. The agreement is as good as those of the SCF-Hartree-Fock, Discrete Variational-Xα, and LCAO-Xα methods. For the first time the overlapping sphere modification has been used to calculate binding curves and results in equilibrium bond lengths for CO, N₂, and F₂ all within 0·3 a ₀ (0·16 Å) of the experimental values, a dramatic improvement over the muffin-tin results. The variation of the calculated ionization potentials under a moderate change in the amount of sphere overlap is found to be rather small, being of the order of the differences between the DV-Xα and LCAO-Xα methods, both of which completely avoid the muffin-tin approximation.     

Blue and red shifts in Rg···HCN and Rg···HNC complexes (Rg=He,Ne, Ar,Kr)

The shift in the harmonic vibrational frequency of the H–C stretch of HCN on formation of the linear Rg···HCN complexes, and of the H–N stretch of HNC on the formation of Rg···HNC complexes (Rg?=?He, Ne, Ar, Kr), has been determined by ab initio computations. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivatives of the interaction energy with respect to displacement of the H–C (H–N) bond length from its equilibrium value in the monomer. Small blue shifts were obtained for He···HCN, Ne···HCN and He···HNC, while red shifts were obtained for the other weakly bound complexes. These vibrational characteristics are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. For all complexes, the IR intensity of the H–C or H–N stretch was increased from the isolated monomer values on complexation.     

The effect of the hydrogen fluoride chain on the aromaticity of C6H6 in the C6H6···(HF)1–4 complexes

The effect of the hydrogen fluoride chain ((HF)_n) on the aromaticity and π character of C–C bonds of C₆H₆ in the C₆H₆···(HF)_n (n = 1–4) complexes were investigated using density functional theory employing RM05 functional. It was found that the binding energy between C₆H₆ and different (HF)_n chains showed a maximum at n = 3 (C₆H₆···(HF)₃). Also, the π–hydrogen interaction (πHI) and the bifurcated fluorine interaction (BFI) increased and decreased the π character of the C–C bond of C₆H₆, respectively. In addition, the change of aromaticity of the C₆H₆ due to the interaction with the HF chains was also studied using three different aspects such as aromatic fluctuation index (FLU), average two centre index (ATI) and proton nuclear magnetic resonance (HNMR) spectrum. The most change in the aromaticity happens when the C₆H₆ interacts with (HF)₃ chain. The variation of aromaticity with the binding energy and the summation of two-body terms were investigated and very good linear correlations were observed.     

The effect of hydrogen-bonding cooperativity on the strength and properties of σ-hole interactions: an ab initio study

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to investigate the effect of hydrogen-bonding cooperativity on the strength and bonding properties of σ-hole interaction in linear FCl???(NCH)_n=2–5, FHS???(NCH)_n=2–5, FH₂P???(NCH)_n=2–5 and FH₃Si???(NCH)_n=2–5 clusters. It is found that the cooperative effects in the hydrogen-bonding tend to strengthen the σ-hole interaction. However, these effects are almost saturated in the larger clusters (n > 5). For a given cluster, the amount of bond contraction in FCl???(NCH)_n is more important than other systems. A nice linear relationship is found between the σ-hole bond energies and absolute ¹⁵N chemical shieldings or spin–spin coupling constants across the σ-hole bond.     

稀有气体化合物MRg~+和MRgF(M=Co,Rh,Ir,Rg=Ar,Kr,Xe)的成键分析（英文）

本文运用B3LYP、MP2、MP4(SDQ)和CCSD(T)方法对由稀有气体原子(Ar,Kr,Xe)与过渡金属原子(Co,Rh,Ir)形成的化合物MRg~+和MRgF进行了几何结构优化和频率计算,并探究了这些化合物的热力学性质.结果表明,MRg+在热力学上是稳定的,而MRgF在热力学上为亚稳态.同时使用分子中的原子理论的电子密度拓扑分析方法、自然键轨道分析方法、能量分解分析方法等多种分析方法来解析M-Rg的成键性质.结果显示,化合物MRg~+的单位正电荷主要分布在金属M上,且这类化合物中金属的电子密度分布与单价离子M~+相似,因此MRg~+中的M-Rg键弱且不共价.与MRg~+相比,MRgF中的M-Rg键长更短(接近于M与Rg原子的理论共价半径之和),Wiberg键级指数更大,具有部分共价性质.     

The effects of a static magnetic field on the microwave absorption of hydrogen plasma in carbon nanotubes： a numerical study

We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton-Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the exter- nal static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

Short-range order and its effect on the electronic structure of binary alloys: CuZn — a case study

We discuss an application of the generalized augmented space method introduced by one of us combined with the recursion method of Haydock et al (GASR) to the study of electronic structure and optical properties of random binary alloys. As an example, we have taken the 50-50 CuZn alloy, where neutron scattering indicates the existence of short-range order.      

The influence of the spin-orbital bond on direct photonuclear reactions (γ, n) and (γ, p)

The Courant model for direct photonuclear reactions is modified by using the wave functions of a shell model with spin-orbital bond. It is shown that the introduction of spin-orbital interaction does not influence the cross-section. The changes caused by the spin-orbital bond are apparent only on the angular distribution, which has the Courant forma+bsin² , but with a different value ofb/a, i.e. the anisotropy coefficient. New selection lawsj j, j j±1 are found. The introduction of spin-orbital interaction permits the negative value of the anisotropy coefficient, found in some experimental papers, to be explained in a natural way.

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: - . , . , - , , a+bsin² , , b/a, . . . j j, j j±1. - , .

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Excerpt from diploma work done at Faculty of Technical and Nuclear Physics in Prague.

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In conclusion the author thanks lecturer J. Kvasnica for the choice of subject and valuable remarks.