Theoretical Study on the Bromomethane−Water 1:2 Complexes

Investigations into the Nature of Halogen Bonding Including Symmetry Adapted Perturbation Theory Analyses

In recent years it has been recognized that, because of their unique properties, halogen bonds have tremendous potential in the development of new pharmaceutical compounds and materials. In this study we investigate the phenomenon of halogen bonding by carrying out ab initio calculations on the halomethane-formaldehyde complexes as well as the fluorine substituted FnH3-nCX···OCH2 dimers, where the halogen bonding halogens (X) are chlorine, bromine, and iodine. Coupled cluster (CCSD(T)/aug-cc-pVTZ) calculations indicate that the binding energies for these type of interactions lie in the range between -1.05 kcal/mol (H3CCl···OCH2) and -3.72 kcal/mol (F3CI···OCH2). One of the most important findings in this study is that, according to symmetry adapted perturbation theory (SAPT) analyses, halogen bonds are largely dependent on both electrostatic and dispersion type interactions. As the halogen atom involved in halogen bonding becomes larger the interaction strength for this type of interaction also gets larger and, interestingly, more electrostatic (and less dispersive) in character. Halogen bonding interactions also become stronger and more electrostatic upon substitution of (the very electronegative) fluorines onto the halomethane molecule.

Molecular Simulations of Halomethanes at the Air/Ice Interface

Halogenated organics are emitted into the atmosphere from a variety of sources of both natural and anthropogenic origin. Their uptake at the surface of aerosols can affect their reactivity, for example, in processes that take part in ozone destruction due to production of reactive chlorine, bromine, and iodine radicals. Classical molecular dynamics (MD) simulations are carried out to investigate the interaction of small halomethane molecules of atmospheric relevance with a crystalline ice surface. The following halomethanes were studied: CH3Cl, CH2Cl2, CHCl3, CH3Br, CH2Br2, and CHBr3. MD simulations provide an invaluable insight into the adsorption behavior of halomethanes species. The adsorption energy is increasing as the number of halogen atoms is increasing. Moreover, brominated methanes exhibit a stronger interaction with the ice than their chlorinated analogs. Implications for the atmospheric chemistry are discussed.

Formation of supramolecular structures in organic solvents

The unusual interactions in organic liquids such as methane derivatives, arenes, and alkanes by the infrared (IR) method were revealed. The transformations of molecular shapes, arising from nonclassical hydrogen and dihydrogen bonds, as well as water factor provide the existence of supramolecular structures in organic fluids. The interpretation of the obtained results in terms of the quantum-chemical calculations has been suggested.

Concerted interaction between pnicogen and halogen bonds in XCl-FH2P-NH3 (X=F, OH, CN, NC, and FCC)

We analyze the interplay between pnicogen-bonding and halogen-bonding interactions in the XCl-FH(2)P-NH(3) (X=F, OH, CN, NC, and FCC) complex at the MP2/aug-cc-pVTZ level. Synergetic effects are observed when pnicogen and halogen bonds coexist in the same complex. These effects are studied in terms of geometric and energetic features of the complexes. Natural bond orbital theory and Bader's theory of "atoms in molecules" are used to characterize the interactions and analyze their enhancement with varying electron density at critical points and orbital interactions. The physical nature of the interactions and the mechanism of the synergetic effects are studied using symmetry-adapted perturbation theory. By taking advantage of all the aforementioned computational methods, the present study examines how both interactions mutually influence each other.

THEORETICAL STUDY OF THE HYDROGEN BOND CHARACTER BETWEEN THE FNO AND HO2 RADICAL

The hydrogen-bonding characters between FNO and HO2 radical are studied systematically with the MPWB1K method and 6-311++G (d, p), aug-cc-PVDZ as well as aug-cc-PVTZ basis sets. The relevant geometrical characteristics, energy properties, and the characters of the intramolecular hydrogen bonds have been reported in this work. In addition, the changes of electrostatic potential density are presented for further understanding the nature of hydrogen bonds and the preference of F atom as the hydrogen-bonding site.

THE COOPERATIVITY BETWEEN HYDROGEN AND HALOGEN BONDS

The cooperativity between hydrogen bonds and halogen bonds in X–HCN–Y ( X: C2H2, H2O, NH3, HCI, HCN, HF; Y: HF, BrF, Br2 is analyzed with MP2/6-311++G(d, p) and DFT/6-311++G(d, p) calculations using the B3LYP and mPW1PW91 hybrid functionals. The results from the quantum chemical calculations are typically clustered in groups according to the Y-ligand. By choosing the X–HCN–HF group as reference it is possible to describe the interaction between the hydrogen and the halogen bond with a two-parameter model. The value of the first parameter of the model describes the contribution of the X -ligand to the interbond cooperativity in the reference cluster. The second parameter of our model quantifies the changes in interbond cooperativity upon varying the Y -ligand. This simple model can be used to predict the cooperativity in X–HCN–Y trimers with reasonable accuracy and thereby to organize the results systematically. It is further shown that the conclusions drawn from this ordering scheme are independent from the computational method and thereby generally applicable.

The role of CS₂ in CS₂/NMP mixed solvent in weakening the hydrogen bond of OH-N in coal: a DFT investigation

The interaction processes of trace amounts of N-methyl-2-pyrrolidinone (NMP), CS(2)/NMP (1:1 by volume) and pure NMP solvent with the hydrogen bond of OH⋯N in coal were constructed and simulated by density functional theory methods. The distances and bond orders between the main related atoms, and the hydrogen bond energy of OH⋯N were calculated. The calculated results show that pure NMP solvent does not weaken the hydrogen bond of OH⋯N in coal. However, trace amounts of NMP and CS(2)/NMP (1:1 by volume) have a strong capacity to weaken the hydrogen bond of OH⋯N in coal. The H2-N3 distances are elongated from 1.87 Å to 3.80 Å and 3.44 Å, the bond orders of H2-N3 all disappear, and the corresponding hydrogen bond energies of OH⋯N in coal decrease from 45.72 kJ mol(-1) to 7.06 and 11.24 kJ mol(-1), respectively. These results show that CS(2) added to pure NMP solvent plays an important role in releasing the original capacity of NMP to weaken the hydrogen bond of OH⋯N in coal, in agreement with experimental observations.

Weak H-bonds. Comparisons of CH···O to NH···O in proteins and PH···N to direct P···N interactions

Whereas CH···O H-bonds are usually weaker than interpeptide NH···O H-bonds, this is not necessarily the case within proteins. The nominally weaker CH···O are surprisingly strong, comparable to, and in some cases stronger than, the NH···O H-bonds in the context of the forces that hold together the adjacent strands in protein β-sheets. The peptide NH is greatly weakened as proton donor in certain conformations of the protein backbone, particularly extended structures, and forms correspondingly weaker H-bonds. The PH group is a weak proton donor, but will form PH···N H-bonds. However, there is a stronger interaction in which P can engage, in which the P atom, not the H, directly approaches the N electron donor to establish a direct P···N interaction. This approach is stabilized by the same sort of electron transfer from the N lone pair to the P-H σ* antibond that characterizes the PH···N H-bond.

Chalcogen bond: a sister noncovalent bond to halogen bond

A sister noncovalent bond to halogen bond, termed chalcogen bond, is defined in this article. By selecting the complexes H(2)CS...Cl(-), F(2)CS...Cl(-), OCS...Cl(-), and SCS...Cl(-) as models, the bond-length change, interaction energy, topological property of the electron charge density and its Laplacian, and the charge transfer of the chalcogen bond have been investigated in detail theoretically. It was found that the similar misshaped electron clouds of the chalcogen atom and the halogen atom result in the similar properties of the chalcogen bond and the halogen bond. Experimental results are in good agreement with the theoretical predictions.

Competition of hydrogen bonds and halogen bonds in complexes of hypohalous acids with nitrogenated bases

A theoretical study of the complexes formed by hypohalous acids (HOX, X = F, Cl, Br, I, and At) with three nitrogenated bases (NH 3, N 2, and NCH) has been carried out by means of ab initio methods, up to MP2/aug-cc-pVTZ computational method. In general, two minima complexes are found, one with an OH...N hydrogen bond and the other one with a X...N halogen bond. While the first one is more stable for the smallest halogen derivatives, the two complexes present similar stabilities for the iodine case and the halogen-bonded structure is the most stable one for the hypoastatous acid complexes.

Theoretical study of complexes and fluoride cation transfer between N2F+ and electron donors

A theoretical study of the complexes formed by the N2F cation (fluorodiazonium ion) and a series of small molecules containing nitrogen atoms have been carried out at the MP2 computational level. In addition, fluorine transfer has been studied. The electron density, NMR shielding and indirect coupling constants of the complexes have been evaluated. The covalent or halogen bonding characteristics of the N...F interactions observed in the complexes are defined by the interatomic distance. It has been determined that the limiting value is 1.6 A.

Triangular halogen trimers. A DFT study of the structure, cooperativity, and vibrational properties

Triangular halogen trimers (RX)3, where X = Br, I and R represents H, H3C, H2FC, HF2C, F3C, CH2=CH, CH[triple bond]C, and Ph, have been investigated using the density functional theory in the Perdew, Burke, and Ernzerhof method. We report herein the optimized geometries of the stable structures, their vibrational frequencies, and binding energies with the two- and three-body terms. All trimer structures possess a cyclic array of halogen atoms in the type II approach by virtue of the nonspherical atomic charge distribution around the halogens. The Br...Br interactions in trimers are very weak, whereas the I...I interactions in trimers are relatively stronger. While all bromine trimers and most of iodine trimers are predicted to be noncooperative, three of iodine trimers show weak cooperativity. The analysis of vibration modes reveals that all halogen trimers exhibit no especially remarkable frequency shifts. It is also shown that the electrostatic contribution plays a major role in the halogen...halogen interactions in halogen trimers. In contrast to bromine trimers, the relative contribution of charge-transfer component to the halogen...halogen interactions becomes more important for iodine trimers.

Stabilities and Properties of Complexes Pairing Hydroperoxyl Radical with Monohalomethanes

UMP2/aug-cc-pvdz calculations are used to analyze the interaction between hydroperoxyl radical (HOO) and CH(3)X (X = F, Cl, Br). Two minima are located on the potential energy surface of each complex. The more strongly bound contains a OH...X bond, along with CH...O; only CH...O bonds occur in the less stable minimum. Binding energies of the dominant minimum lie in the range of 20-24 kJ/mol, with X = F the most strongly bound. Analysis of the perturbations of the covalent bond lengths within each subunit caused by complexation, coupled with vibrational frequencies and charge transfers, opens a window into the nature of the interactions.