Insight into the halogen-bond nature of noble gas-chlorine systems by molecular beam scattering experiments, ab initio calculations and charge displacement analysis

Abstract

A weak halogen bond, together with charge transfer from a noble gas to Cl2, characterizes the intermolecular interaction between a noble gas atom and Cl2 in a collinear configuration.

Complexes of helium with neutral molecules: Progress toward a quantitative scale of bonding character

“…We first compared our predicted geometries and interaction energies with the accurate values available from the literature for the majority of the presently investigated He(M) systems (the only previously unreported are the HeClR, R = CN, CCH, OH, SH, CH 3 , SiH 3 ). With respect to these benchmark data (listed in Table S3), typically obtained at the CCDS(T) or SAPT levels of theory with very large basis sets, the bond distances quoted in Figure , and the listed in Table feature a mean unsigned deviation (MUD), respectively, of 0.0908 a 0 , and 1.20 cm −1 .…”

“…When the CT takes place, it is convenient to come up with a definite numerical estimate, which can be done by taking the value of the CD curve at a specific point between the fragments. Based on previous studies, we choose to separate the fragments and to extract the CT at the so‐called isodensity boundary (IB), that is, at the point along z where the electron densities of the noninteracting fragments become equal.…”

“…The Ng(M) are, in particular, usually perceived as typical van der Waals molecules, held together by the favorable balance between dispersion and repulsion. The Ng, however, while generally resistant to share their electrons so to form true ionic or covalent bonds, sensibly respond to the polarization effects exerted by the ligands, and even the complexes with nonpolar molecules may include not only inductive, but also CT stabilizing components . In particular, searching for a mode to analyze this transition in the bonding character, we recently obtained evidence for a new quantitative index that is generally informative about the interactions occurring in noncovalent Ng complexes.…”

Noncovalent Complexes of the Noble‐Gas Atoms: Analyzing the Transition from Physical to Chemical Interactions

“…When the CT takes place, it is convenient to come up with a definite numerical estimate, which can be done by taking the value of the CD curve at a specific point between the fragments. According to our previous studies, we choose to separate the fragments and to extract the CT at the so‐called isodensity boundary, that is, at the point along z where the electron densities of the noninteracting fragments become equal.…”

“…The latter contribution is particularly relevant, as it marks the transition from a purely (or nearly purely) “physical” contact to a more specific “chemical” noncovalent bond. In particular, some of us recently ascertained that the CT plays a major role in the complexes of the Ng atoms, particularly He, Ne, and Ar, with H 2 O, NH 3 , CCl 4 , and Cl 2 . These systems could be, actually, assigned as remarkable examples of “nascent” hydrogen and halogen bonds.…”