π-Electron “Donor-Acceptor” Complexes B⋅⋅⋅ClF and the Existence of the “Chlorine Bond”

The Interaction of Water and Dibromine in the Gas Phase: An Investigation of the Complex H2O⋅⋅⋅Br2 by Rotational Spectroscopy and Ab Initio Calculations

“…This makes it clear that all of these complexes obey the rule originally put forward to account for the observed geometries of hydrogenbonded complexes B ¥¥¥ HX [44,45] and recently extended [4,5] to include complexes B ¥¥¥ XY involving dihalogen molecules. The rules require that the nucleophilic end d H of HX or d X of XY seeks the axis of a nonbonding or p-bonding electron pair carried by the electron-donor atom of B.…”

“…Similar conclusions have been reached for H 2 O ¥¥¥ HF [29] and H 2 O ¥¥¥ HCl, [21] strengthening the case for the halogen bond in B ¥¥¥ XY complexes, as recently postulated. [4,5] Experimental Section…”

Prereactive Complexes of Dihalogens XY with Lewis Bases B in the Gas Phase: A Systematic Case for the Halogen Analogue B⋅⋅⋅XY of the Hydrogen Bond B⋅⋅⋅HX

“…In view of the foregoing, it seems worthwhile to define a halogen bond [152] that is an analogue of the hydrogen bond. Thus, the halogen bond is predominantly electrostatic in origin and involves the interaction of unperturbed electric charge distributions of B and XY.…”

Thermodynamic and Spectroscopic Scales of Halogen‐Bond Basicity and Affinity

“…In addition to leading to geometries, rotational spectroscopy has also provided halogenbond stretching force constants (k σ ) for many dimers B· · ·X Y. For example, from the values of k σ for B· · ·ClF [48], the ranking of π and pseudo-π bases is benzene < 1,3-butadiene < allene < cyclopropane ≈ acetylene ≈ methylenecyclopropane < ethylene. Strictly, they measure the restoring force per unit infinitesimal displacement of the halogen bond.…”