Structures of Clusters Surrounding Ions Stabilized by Hydrogen, Halogen, Chalcogen, and Pnicogen Bonds

Four H-binding HCl and HF molecules position themselves at the vertices of a tetrahedron when surrounding a central Cl-. Halogen bonding BrF and ClF form a slightly distorted tetrahedron, a tendency that is amplified for ClCN which forms a trigonal pyramid. Chalcogen bonding SF2, SeF2, SeFMe, and SeCSe occupy one hemisphere of the central ion, leaving the other hemisphere empty. This pattern is repeated for pnicogen bonding PF3, SeF3 and AsCF. The clustering of solvent molecules on one side of the Cl- is attributed to weak attractive interactions between them, including chalcogen, pnicogen, halogen, and hydrogen bonds. Binding energies of four solvent molecules around a central Na+ are considerably reduced relative to chloride, and the geometries are different, with no empty hemisphere. The driving force maximizes the number of electronegative (F or O) atoms close to the Na+, and the presence of noncovalent bonds between solvent molecules

Structures and Energetics of Clusters Surrounding Diatomic Anions Stabilized by Hydrogen, Halogen, and other Noncovalent Bonds

Diatomic anions CN-, NO-, and OH- are surrounded by 2, 3, and 4 ligand molecules drawn from the HF, HCl, XF, YF2, ZF3, TF4, and TrF3 set wherein X= Cl,Br, Y=S,Se, Z=P,As, T=Si,Ge, and Tr=Al,Ga. In the case of two ligands, both interact with the N of NO- and the O of OH-, but one approaches either end of CN-. Unlike the H and halogen bonding units, as the number of ligands increases there is a tendency for chalcogen, pnicogen, tetrel, and triel-bonding ligands to form a cage around the central anion, with strong inter-ligand noncovalent bonds. There are a number of unusual features observed as well, including proton transfers from the ligands to the central anion, halogen atom sharing, linearization of normally highly bent YF2 molecules, F-sharing between tetrel atoms, and OH-⸳⸳F H-bonds. Triel-bonding ligands engage in the strongest binding but the patterns of the other types of ligands depend upon the particular central anion and the number of ligands involved

Halogen Bonds Formed Between Substituted Imidazoliums and N Bases of Varying N-Hybridization

Heterodimers are constructed containing imidazolium and its halogen-substituted derivatives as Lewis acid. N in its sp3, sp2 and sp hybridizations is taken as the electron-donating base. The halogen bond is strengthened in the Cl \u3c Br \u3c I order, with the H-bond generally similar in magnitude to the Br-bond. Methyl substitution on the N electron donor enhances the binding energy. Very little perturbation arises if the imidazolium is attached to a phenyl ring. The energetics are not sensitive to the hybridization of the N atom. More regular patterns appear in the individual phenomena. Charge transfer diminishes uniformly on going from amine to imine to nitrile, a pattern that is echoed by the elongation of the C-Z (Z=H, Cl, Br, I) bond in the Lewis acid. These trends are also evident in the Atoms in Molecules topography of the electron density. Molecular electrostatic potentials are not entirely consistent with energetics. Although I of the Lewis acid engages in a stronger bond than does H, it is the potential of the latter which is much more positive. The minimum on the potential of the base is most negative for the nitrile even though acetonitrile does not form the strongest bonds. Placing the systems in dichloromethane solvent reduces the binding energies but leaves intact most of the trends observed in vacuo; the same can be said of ∆G in solution

Systematic Elucidation of Factors that Influence the Strength of Tetrel Bonds

Quantum calculations are used to examine the properties of heterodimers formed by a series of tetrel-containing molecules with NH3 as universal Lewis base. TH4 was taken as a starting point, with T= C, Si, Ge, and Sn. The H atoms were replaced by various numbers of F atoms: TH3F, TF3H, and TF4 so as to monitor the effects of adding electron-withdrawing substituents. Unsubstituted TH4 molecules form the weakest tetrel bonds, only up to about 2 kcal/mol. The bond is strengthened when the H opposite NH3 is replaced by F, rising up to the 6-9 kcal/mol range. Another means of strengthening arises when the three peripheral H atoms of TH4 are replaced by F. The effect of the latter is heavily dependent on the nature of the T atom, and is particularly noticeable for larger tetrels. The two sorts of fluorination patterns are cooperative, in that their combination in TF4 yields by far the most powerful tetrel bonding agent. The tetrel bond is strengthened as the T atom moves further down the periodic table column. The strongest bond amounts to 25.5 kcal/mol for SnF4••NH3. A number of features correlate with the binding energy, but only roughly. These properties include the charge transfer, the AIM bond critical point electron density, the molecular electrostatic potential, and the stretch of the T-X covalent bond upon complex formation

Computational Study About Noncovalent Bonding Systems Involving Halogen, Chalcogen and Pnicogen Bonds

First terms used in this thesis are introduced and defined as follows. In the periodic table, the elements in the 17th column are named halogen including fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). The elements in the 16th column are named chalcogen including oxygen (O), sulfur (S), selenium (Se) and tellurium (Te). The elements in the 15th column are named pnicogen including nitrogen (N), phosphorus (P), arsenic (As) and antimony (Sb). After hydrogen bonds (B-H⋅⋅⋅B) are well studied and understood by scientists and researchers, halogen bonds (R-X⋅⋅⋅B) have drawn attention due to the similarities in bonding format and geometries. However, it is not straightforward to understand how the overall negative halogen atoms interact with the electronegative chemical group, which is usually a Lewis base until scientists proved the existence of the positive region surrounding the halogen atom X directly opposite the R group by Molecular Electrostatic Potential analysis. This thesis studied the detailed structural, geometric and spectroscopic features quantitatively by computational chemistry. The research studied the halogen transfer in symmetric (between two same molecules) and asymmetric systems (between two different molecules). In either case, the potential contains a single symmetric well for short halogen bond length and transferred to a double well when the distance was increased. Furthermore, the partial transfer calculations of halogen as bridging atom between two molecules suggests the degree of halogen transfer to form an ion pair is small even when a strong acid is combined with a strong base. Moreover, the thesis extended the application of Badger-Bauer rules from hydrogen bonds to halogen, chalcogen and pnicogen bonds. Badger-Bauer rules states the spectroscopic change were linearly related to the bond strength of hydrogen bonds. The theory extension will improve the understanding of bond strength of a specific bond in the complicated systems by detecting the spectroscopic change