Directional tendencies of halogen and hydrogen bonds

Abstract

Halogen bonding, RAXÁÁÁB, and hydrogen bonding, RAHÁÁÁB, are electrostatically-driven noncovalent interactions of covalently-bonded halogens RAX and hydrogens RAH with negative sites B. A significant difference between halogen and hydrogen bonding is that the former is typically near-linear (the R-X-B angles are close to 180 ), whereas the latter is more likely to be nonlinear (R-H-B angles sometimes considerably less than 180). In this work, we have looked at the properties of several RABrÁÁÁB and RAHÁÁÁB complexes as functions of these angles. The differences in the directional tendencies in these interactions can be attributed to the presence of nonbonding valence electrons on the bromines, and their absence on hydrogen. We also found that for a given negative site, the halogen and hydrogen bonding interaction energies correlate very well with the positive electrostatic potentials created at it by RAX and RAH. This attests to the electrostatically-driven nature of these interactions. Overall, this study provides support for regarding both halogen and hydrogen bonding as subsets of r-hole interactions.

σ-Holes on Transition Metal Nanoclusters and Their Influence on the Local Lewis Acidity

“…Simultaneously a negative electrostatic potential is built up on F. Due to the spherical symmetry of the H 1s orbital, the corresponding σs-hole is diffused over the entire H end of the molecule. This explains the weak directionality of H-bond interactions, which often deviate significantly from 180° [8]. In the following we will show that common features of σs-holes are their diffuse and non-directional character.…”

“…Owing to the largely directional character of the pz orbitals, the σp-holes are highly localized in the direction of the σ-bond. Consequently, the halogen bond interactions are, in contrast to hydrogen bonds, found to be directional with A···X-R angles close to 180° [8].…”

“…As expected, the cubic Au 8 (singlet) display V S,max at the corner sites. Although the cubic structure is not stable for Au 8 , it relaxes to a structure with T d symmetry ( Figure 3) that still display V S,max at corner sites. It is worth noting at this point that the location of the σ s -holes of Au 8 at positions deviant from the extensions of the TM-TM bonds suggest that they may not be proper σ-holes; the V S,max are positioned at angles deviant from straight (180 • ) or right (90 • ) with respect to the σ-bonds of the cluster.…”

“…For Pt 8 , the nonet spin-state means that each atom has a magnetic moment of 1. The partially occupied orbitals of Pt 8 This gives rise to the triangular shaped V S,max at the corner atoms of the cubic O h Ir 8 nanocluster.…”

Electrostatic Potentials, Intralattice Attractive Forces and Crystal Densities of Nitrogen-Rich C,H,N,O Salts

“…The surfaces of 3 and 4 are completely negative, although with some local variation, which will be discussed later; the surface of the cation NH 4 + is completely positive ( and on the ammonia molecule (on which they vary from´40 to +24 kcal/mol [21]). It follows that the Coulombic attractions between the ions in the two salts will be much stronger than between the neutral molecules in the molecular solids 1 and 2.…”