Agnieszka J. Gordon

On the multiple B–N bonding in boron compounds using the topological analysis of electron localization function (ELF)

Topological analysis of the Electron Localization Function (ELF) within the framework of Quantum Chemical Topology (QCT) has been applied to study the nature of the boron–nitrogen bonds. A series of 10 compounds have been chosen, with the B–N bond length ranging between 1.698 A (B–N) and 1.258 A (BN). According to the Lewis formula three types of bonds have been recognized. These are: the single B–N bond with a basin population of 1.91 ÷ 2.09e, the double BN bond with a population of 3.78 ÷ 4.28e, and the triple BN bond with a basin population of 5.72 ÷ 5.74e. In the case of partial double bonds (BN), where formally two or more resonance hybrids have to be considered, our calculations strongly support the concept of double boron–nitrogen bonding (BN).

Nature of the bonding in the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I) molecules. Topological study on electron density and the electron localization function (ELF).

Topological analysis of the electron localization function (ELF) has been carried out for the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I) molecules using the wave function approximated by the CCSD, MP2, and DFT(B3LYP, M062X) methods including zero-order regular approximation (ZORA). In the Ng-F bond, the bonding disynaptic attractor V(Ng,F) is missing; therefore, there are no signs of the covalent binding. The nature of the Au-Ng bond depends on the computational method used. Analysis of the ELF carried out for the AuArF and AuXeF molecules, with the wave function approximated by the CCSD and MP2 methods, shows the V(Au,Ng) attractor possibly corresponding to a partially covalent binding between the gold and noble gas atom. However, its very small basin population (<1e) and a very large value of the variance of the basin population suggest that the Au-Ng bond has a very delocalized character. Such bond nature may be related to the charge shift concept with a resonance of the Au(-+)NgX, Au(+-)NgX hybrids. The weakest Au-Ng bond, in terms of the smallest amount of electron density for the V(Au,Ng) basin, is found for the AuKrF molecule with the CCSD method (0.13e). The MP2 method, however, does not yield any V(Au, Ng) population; hence, the covalent Au-Kr bond is not confirmed. Because the V(Au,Ng) attractor is also not observed with the DFT method, the proper characterization of the Au-Ng bond requires proper description of correlation effects. Additional studies on the Au2 and [AuXe](+) molecules, performed at the CCSD and B3LYP levels, exhibit no V(Au,Au) and V(Au,Xe) bonding basins either.

Electron localization function and electron localizability indicator applied to study the bonding in the peroxynitrous acid HOONO

The ground‐state electronic structure of peroxynitrous acid (HOONO) and its singlet biradicaloid form (HO···ONO) have been studied using topological analysis of the electron localization function (ELF), together with the electron localizability indicator (ELI‐D), at the DFT (B3LYP, M05, M052X, and M06), CCSD, and CASSCF levels. Three isomers of HOONO (cis‐cis, cis‐perp, and trans‐perp) have been considered. The results show that from all functionals applied, only B3LYP yields the correct geometrical structure. The ELF and ELI‐D‐topology of the OO and central NO bonds strongly depends on the wave function used for analysis. Calculations carried out at CAS (14,12)/aug‐cc‐pVTZ//CCSD(T)/aug‐cc‐pVTZ level reveal two bonds of the charge‐shift type: a protocovalent NO bond with a basin population of 0.82–1.08e, and a more electron depleted OO bond with a population of 0.66–0.71e. The most favorable dissociation channel (HOONO → HO + ONO) corresponds to breaking of the most electron‐deficient bond (OO). In the case of cis‐ and trans‐HO···ONO, the ELF, ELI‐D, and electron density fields results demonstrate a closed‐shell O···O interaction. The α‐spin electrons are found mainly (0.64e) in the lone pairs of oxygen Vi = 1,2 (O) from the OH group. The β‐spin electrons are delocalized over the ONO group, with the largest concentration (0.34e) on the lone pair of nitrogen V(N).

Electron localization function study on intramolecular electron transfer in the QTTFQ and DBTTFI radical anions.

The unsymmetrical distribution of the unpaired electron in the ground state of the DBTTFI(•-) radical anion (bi(6-n-butyl-5,7-dioxo-6,7-dihydro-5H-[1,3]dithiolo[4,5-f]isoindole-2-ylidene) is theoretically predicted using the M06-2X/6-31+G(d,p) level of calculations. The results are additionally confirmed by single point calculations at B3LYP/aug-cc-pVTZ, LC-ωPBE/aug-cc-pVTZ, and M06-2X/aug-cc-pVTZ levels. DBTTFI, containing the TTF (tetrathiafulvalene) fragment, may be used in the construction of organic microelectronic devices, similarly to the radical anion of QTTFQ. The unsymmetrical distribution of spin density in (QTTFQ)(•-) has been confirmed using M06-2X/aug-cc-pVTZ calculations, with subsequent study using topological analysis of electron localization function (ELF). The reorganization of the chemical bonds during intramolecular electron transfer in (QTTFQ)(•-) and (DBTTFI)(•-) has been analyzed using bonding evolution theory (BET). The reaction path has been simulated by the IRC procedure, and the evolution of valence basins has been described using catastrophe theory. The simple mechanisms: (QTTFQ)(•-): η-1-3-CC(+)-0: (-•)(QTTFQ) and (DBTTFI)(•-): η-1-3-[F](4)[F(+)](4)-0: (-•)(DBTTFI), each consisting of three steps, have been observed. Two cusp or 4-fold catastrophes occur immediately after the TS. Our study shows that potential future microelectronic devices, constructed on the basis of the (QTTFQ)(•-) and (DBTTFI)(•-) systems, should exploit the properties of the C═C bond.

The DFT study on the reaction between benzaldehyde and 4-amine-4H-1,2,4-triazole and their derivatives as a source of stable hemiaminals and schiff bases. Effect of substitution and solvation on the reaction mechanism

AbstractReaction mechanism for the benzaldehyde (ald) and 4-amine-4H-1,2,4-triazole (4at) has been investigated at the DFT (B3LYP)/6–31+G(d) computational level. Three transition states (TS) have been identified. The TS1 corresponds to hydrogen transfer from the NH2 group to the C = O bond and nucleophillic attack of the carbon atom from the aldehyde group on the nitrogen atom from the NH2 group in 4at. The result of this reaction is the hemiaminal molecule. The TS2 characterises an internal rearrangement of the benzene and triazole rings in the hemiaminal molecule. The TS3 leads to breaking of the O-H bond, the elimination reaction of the H2O molecule, and formation of the C=N bond. The final product of this reaction is a Schiff base. In order to determine the most favorable conditions for hemiaminal formation, the influence of electronic structure modification on the energetic properties during the reaction of benzaldehyde and 4-amine-4H-1,2,4-triazole has been studied. Thirteen substituents: NH2, OH, OCH3, CH3, F, I, Cl, Br, COH, COOH, CF3, CN, NO2, with different Hammett’s constant values (σ = −0.66–+0.78) have been considered. Finally, the reaction mechanism has been investigated in the presence of 1 to 5 water molecules. Graphical AbstractThe R substituent effect on the energetics of the reaction between (modified) benzaldehyde (R-ald) and 4-amine-4H-1,2,4-triazole

Electron localization function study on the chemical bonding in a real space for tetrahedrane, cubane, adamantane, and dodecahedrane and their perfluorinated derivatives and radical anions.

The nature of chemical bonding in caged cycloalkanes CnXn, CnFn(-•), (n = 4, 8, 20; X = H, F), and C10X16, C10F16(-•), (X = H, F) has been investigated using topological analysis of the ELF function, electron density, and the Laplacian of electron density at density functional theory (DFT) level. The bonding analysis performed for the perfluorinated radical anion of dodecahedrane (C20F20(-•)), bestowing an additional electron, shows an unexpected local maximum of the ELF inside the carbon cage. The presence of such an attractor confirms the sigma stellation concept presented by Irikura (J. Phys. Chem. A 2008, 112, 983) and essential change of the electron localization inside the cage. The basin belongs to the rare asynaptic type, V(asyn), and its mean electron population is 0.26 (0.36e). The value of the integrated spin density, 0.13e, shows that both spin-up and spin-down electrons reside in the vicinity of the cage center. A similar attractor has been found for perfluorinated radical anion of adamantane (C10F16(-•)). However, the saturation of the basis set suggests that such an attractor may be an artifact. For both caged perfluorinated tetrahedrane and cubane (CnFn (-•), n = 4, 8), no valence attractors are present inside the cage. Unpaired electron density is concentrated mainly on the C-C bonding basins. The results obtained in this study are complementary to those based on the molecular orbital theory presented by Irikura.

On the nature of interactions in the F 2 OXe ... NCCH 3 complex: Is there the Xe(IV)-N bond?

Nature of the bonding in isolated XeOF2 molecule and F2OXe…NCCH3 complexes have been studied in the gas phase (0 K) using Quantum Chemical Topology methods. The wave functions have been approximated at the MP2 and DFT levels of calculations, using the APFD, B3LYP, M062X, and B2PLYP functionals with the GD3 dispersion correction. The nature of the formal XeO bond in the XeOF2 monomer depends on the basis set used (all‐electron vs. the ecp‐28 approximation for Xe). Within the all‐electron basis set approach the bond is represented by two bonding attractors, Vi = 1,2(Xe,O), with total population of about 1.06e and highly delocalized electron density in both bonding basins. No bonding basins are observed using the ecp‐28 approximation. These results shows that the nature of xenon–oxygen is complicated and may be described with mesomeric equilibrium of the Lewis representations: Xe(+)O(−) and Xe(–)O(+). For both the xenon–oxygen and xenon–fluorine interactions the charge‐shift model can be applied. The F2OXe…NCCH3 complex exists in two structures: “parallel,” stabilized by non‐covalent C…O and Xe…N interactions and “linear” stabilized by the Xe…N interaction. Topological analysis of ELF shows that the F2OXe…NCCH3 molecule appears as a weakly bound intermolecular complex. Intermolecular interaction energy components have also been studied using Symmetry Adapted Perturbation Theory.

Ab initio and quantum chemical topology studies on the isomerization of HONO to HNO2. Effect of the basis set in QCT.

The article focus on the isomerization of nitrous acid HONO to hydrogen nitryl HNO2. Density functional (B3LYP) and MP2 methods, and a wide variety of basis sets, have been chosen to investigate the mechanism of this reaction. The results clearly show that there are two possible paths: 1) Uncatalysed isomerisation, trans‐HONO → HNO2, involving 1,2‐hydrogen shift and characterized by a large energetic barrier 49.7 ÷ 58.9 kcal/mol, 2) Catalysed double hydrogen transfer process, trans‐HONO + cis‐HONO → HNO2 + cis‐HONO, which displays a significantly lower energetic barrier in a range of 11.6 ÷ 18.9 kcal/mol. Topological analysis of the Electron Localization Function (ELF) shows that the hydrogen transfer for both studied reactions takes place through the formation of a ‘dressed’ proton along the reaction path. 1 Use of a wide variety of basis sets demonstrates a clear basis set dependence on the ELF topology of HNO2. Less saturated basis sets yield two lone pair basins, V1(N), V2(N), whereas more saturated ones (for example aug‐cc‐pVTZ and aug‐cc‐pVQZ) do not indicate a lone pair on the nitrogen atom. Topological analysis of the Electron Localizability Indication (ELI‐D) at the CASSCF (12,10) confirms these findings, showing the existence of the lone pair basins but with decreasing populations as the basis set becomes more saturated (0.35e for the cc‐pVDZ basis set to 0.06e for the aug‐cc‐pVTZ). This confirms that the choice of basis set not only can influence the value of the electron population at the particular atom, but can also lead to different ELF topology.

Effects of xenon insertion into hydrogen bromide. Comparison of the electronic structure of the HBr···CO2 and HXeBr···CO2 complexes using quantum chemical topology methods: electron localization function, atoms in molecules and symmetry adapted perturbation theory.

Quantum chemistry methods have been applied to study the influence of the Xe atom inserted into the hydrogen-bromine bond (HBr → HXeBr), particularly on the nature of atomic interactions in the HBr···CO2 and HXeBr···CO2 complexes. Detailed analysis of the nature of chemical bonds has been carried out using topological analysis of the electron localization function, while topological analysis of electron density was used to gain insight into the nature of weak nonbonding interactions. Symmetry-adapted perturbation theory within the orbital approach was applied for greater understanding of the physical contributions to the total interaction energy.

On the nature of the boron–copper interaction. Topological study of the electron localisation function (ELF)

Topological analysis of the Electron Localization Function (ELF) has been applied to study the nature of the boron–copper bonds in the BCu molecule and a series of 18 organoboron compounds with bond lengths between 1.994 and 2.671 A. The three-center and two-center covalent bonds have been found through localisation of the V(B,Cu,A), A = Mn, Cu, B, H and C, and V(B,Cu) attractors with the basin populations from 1.49 to 3.13e and from 2.49 to 2.99e, respectively. For ropt(B,Cu) > 2.5 A, B⋯Cu interactions, characterised by very small basin populations, between 0.12 and 0.49e have been observed. Topological analysis of ELF has not proven the existence of a triple BCu bond.