A theoretical investigation of the characteristics of hydrogen/halogen bonding interactions in dibromo-nitroaniline

Visible-light-driven catalyst-free C-S cross-coupling of thiol derivatives and aryl halides

A mild, scalable, and high-yielding visible-light-promoted C-S cross-coupling between alkyl thiol derivatives and (hetero)aryl halides without the need for metals, ligands, or photocatalysts is reported, offering advantages over traditional C-S bond forming strategies. The formation of an electron donor-acceptor (EDA) complex is supported by experimental and computational mechanistic studies, which undergoes visible-light-induced charge transfer to initiate C-S bond formation in the absence of a photoredox catalyst.

Computational Structures and SAPT Interaction Energies of HXeSH···H2Y (Y=O or S) Complexes

Ab initio calculations of the structures, vibrational spectra and supermolecular and symmetry-adapted perturbation theory (SAPT) interaction energies of the HXeOH and HXeSH complexes with H2O and H2S molecules are presented. Two minima already reported in the literature were reproduced and ten new ones were found together with some transition states. All complexes show blue shift in Xe–H stretching mode upon complexation. The computed spectra suggest that it should be possible to detect and distinguish the complexes experimentally. The structures where H2O or H2S is the proton-donor were found to be the most stable for all complex compositions. The SAPT analysis shows significant differences between the complexes with H2O and H2S indicating much larger dispersion and exchange contributions in the complexes with H2S.

A theoretical study on the characteristics of the intermolecular interactions in the active site of human androsterone sulphotransferase: DFT calculations of NQR and NMR parameters and QTAIM analysis

A theoretical study at the level of density functional theory (DFT) was performed to characterize noncovalent intermolecular interactions, especially hydrogen bond interactions, in the active site of enzyme human androsterone sulphotransferase (SULT2A1/ADT). Geometry optimization, interaction energy, (2)H, (14)N, and (17)O electric field gradient (EFG) tensors, (1)H, (13)C, (17)O, and (15)N chemical shielding (CS) tensors, Natural Bonding Orbital (NBO) analysis, and quantum theory of atoms in molecules (QTAIM) analysis of this active site were investigated. It was found that androsterone (ADT) is able to form hydrogen bonds with residues Ser80, Ile82, and His99 of the active site. The interaction energy calculations and NBO analysis revealed that the ADT molecule forms the strongest hydrogen bond with Ser80. Results revealed that ADT interacts with the other residues through electrostatic and Van der Waals interactions. Results showed that these hydrogen bonds influence on the calculated (2)H, (14)N, and (17)O quadrupole coupling constants (QCCs), as well as (1)H, (13)C, (17)O, and (15)N CS tensors. The magnitude of the QCC and CS changes at each nucleus depends directly on its amount of contribution to the hydrogen bond interaction.

Asymmetric bifurcated halogen bonds

Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as 'σ-hole - lone pair' or 'σ-hole - π' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction.

Spectral and thermal characterization of halogen-bonded novel crystalline oligo(p-bromoacetophenone formaldehyde)

A novel oligomer p-bromoacetophenone-formaldehyde (OPBAF) was prepared by condensation polymerization in the presence of an acid as catalyst. It was characterized by FT-IR, NMR, pyrolysis GC/MS, XRD, GPC, and TG-DTG. The crystallographic parameters and space group for hexagonal OPBAF were a = b = 2.0810 Å and c = 9.2340 Å and P3̅m1, respectively. The degradation activation energy of the oligomer was studied by the Kissinger method. The kinetic parameters were also obtained. Halogen bonding interactions in the crystalline oligomers are identified between halogen···carbonyl and halogen···halogen. Little correlation was found in the halogen bonding motifs exhibited as a function of bromine present in this oligomer, and a unique bifurcated Br···Br/Br···O═C halogen bonding synthon was identified. This newly developed oligomer may be used as an interesting material for the development of 3D-designed structural products.

Unstable, metastable, or stable halogen bonding interaction involving negatively charged donors? A statistical and computational chemistry study

The noncovalent halogen bonding could be attributed to the attraction between the positively charged σ-hole and a nucleophile. Quantum mechanics (QM) calculation indicated that the negatively charged organohalogens have no positively charged σ-hole on their molecular surface, leading to a postulation of repulsion between negatively charged organohalogens and nucleophiles in vacuum. However, PDB survey revealed that 24% of the ligands with halogen bonding geometry could be negatively charged. Moreover, 36% of ionizable drugs in CMC (Comprehensive Medicinal Chemistry) are possibly negatively charged at pH 7.0. QM energy scan showed that the negatively charged halogen bonding is probably metastable in vacuum. However, the QM calculated bonding energy turned negative in various solvents, suggesting that halogen bonding with negatively charged donors should be stable in reality. Indeed, QM/MM calculation on three crystal structures with negatively charged ligands revealed that the negatively charged halogen bonding was stable. Hence, we concluded that halogen bonding with negatively charged donors is unstable or metastable in vacuum but stable in protein environment, and possesses similar geometric and energetic characteristics as conventional halogen bonding. Therefore, negatively charged organohalogens are still effective halogen bonding donors for medicinal chemistry and other applications.

Halogen bond interactions enhanced by sodium bonds — Theoretical evidence for cooperative and substitution effects in NCX···NCNa···NCY complexes (X = F, Cl, Br, I; Y = H, F, OH)

Quantum chemical calculations are performed to study cooperativity and substituent effects between halogen bond and sodium bond interactions in NCX···NCNa···NCY complexes, where X = F, Cl, Br, I and Y = H, F, OH. These effects are studied in terms of equilibrium geometry, interaction energy, 15N nuclear magnetic resonance (NMR) parameters, and electron density analysis of the complexes at the MP2/aug-cc-pVTZ level. The X···N and Na···N bond lengths in the ternary systems are always shorter than those in the corresponding dyads. In each triad, the decrease in the halogen bond length is far greater than that of the sodium bond. In all triads studied, a favorable cooperativity is found with values that range between –0.30 and –1.72 kcal/mol. It is revealed that NMR parameters at the site of the nitrogen atom of the NCNa molecule can be regarded as a good description to quantify the degree of cooperative effects in the NCX···NCNa···NCY systems. The nature of halogen bond and sodium bond interactions of the complexes is analyzed using parameters derived from the quantum theory of atoms in molecules methodology and energy decomposition analysis.

CNXeCl and CNXeBr species as halogen bond donors: a quantum chemical study on the structure, properties, and nature of halogen···nitrogen interactions

In the present study, strength and characteristic of halogen bond interactions between CNXeY and NCZ molecules are investigated, where Y = Cl, Br and Z = H, CN, F, OH, CH₃, OCH₃, NH₂. MP2/aug-cc-pVTZ calculations indicate that the interaction energies for CNXeY⋯NCZ complexes lie in the range between -1.0 and -3.1 kcal mol⁻¹. Not surprisingly, the calculated interaction energies show a strong correlation with the negative electrostatic potentials on nitrogen atoms. One of the most important results of this study is that, according to energy decomposition analyses, Cl⋯N halogen bonds are largely dependent on dispersion effects, while electrostatic interactions are the major source of the attraction in Br⋯N bonds. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis are used in this study to deepen the nature of the interactions considered. This appears to be the first report on a halogen bond involving halogenated xenon isocyanides.

On the strength and nature of intermolecular X···O interactions in CF2ClBr−O3 complexes (X = F, Cl, Br): an ab initio investigation

Ab initio calculations were realized to analyze the existence of intermolecular X···O interactions in bromochlorodifluoromethane (CF2ClBr) complexes with ozone, where X = F, Cl, and Br. These calculations have been carried out using MP2 and CCSD(T) methods, through analysis of surface electrostatic potentials V(r), intermolecular interaction energies, and electron density analysis. Coupled cluster (CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ) calculations indicate that the stabilization energies for the CF2ClBr−O3 complexes lie in the range between –3.9 and –7.7 kJ/mol. The characteristic of X···O interactions has been identified in terms of the electron density analysis within the quantum theory of atoms in molecules. Energy decomposition analysis shows that the attractive nature of the X···O interactions within the title complexes is chiefly due to dispersion effects, but electrostatic contribution also plays an important role.

Intramolecular halogen-halogen bonds?

By analysing the properties of the electron density in the structurally simple perhalogenated ethanes, X3C-CY3 (X, Y = F, Cl), a previously overlooked non-covalent attraction between halogens attached to opposite carbon atoms is found. Quantum chemical calculations extrapolated towards the full solution of the Schrödinger equation reveal the complex nature of the interaction. When at least one of the halogens is a chlorine, the strength of the interaction is comparable to that of hydrogen bonds. Further analysis shows that the bond character is quite different from standard non-covalent halogen bonds and hydrogen bonds; no bond critical points are found between the halogens, and the σ-holes of the halogens are not utilised for bonding. Thus, the nature of the intramolecular halogen···halogen bonding studied here appears to be of an unusually strong van der Waals type.

Insights into the strength and nature of carbene···halogen bond interactions: a theoretical perspective

Halogen-bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays critical roles in fields as diverse as molecular biology, drug design and material engineering. In this work, we have examined the strength and origin of halogen bonds between carbene CH₂ and XCCY molecules, where X = Cl, Br, I, and Y = H, F, COF, COOH, CF₃, NO₂, CN, NH₂, CH₃, OH. These calculations have been carried out using M06-2X, MP2 and CCSD(T) methods, through analyses of surface electrostatic potentials V S(r) and intermolecular interaction energies. Not surprisingly, the strength of the halogen bonds in the CH₂···XCCY complexes depend on the polarizability of the halogen X and the electron-withdrawing power of the Y group. It is revealed that for a given carbene···X interaction, the electrostatic term is slightly larger (i.e., more negative) than the dispersion term. Comparing the data for the chlorine, bromine and iodine substituted CH₂···XCCY systems, it can be seen that both the polarization and dispersion components of the interaction energy increase with increasing halogen size. One can see that increasing the size and positive nature of a halogen's σ-hole markedly enhances the electrostatic contribution of the halogen-bonding interaction.