Characterization of Competing Halogen- and Hydrogen-Bonding Motifs in Simple Mixed Dimers of HCN and HX (X = F, Cl, Br, and I)

Abstract

This work performs the first systematic comparison of hydrogen-and halogen-bonded configurations of the HCN/HX mixed dimer, where X = F, Cl, Br, and I. Eleven different minima have been characterized for these four heterogeneous dimers near the CCSD(T) complete basis set (CBS) limit. For each complex, two different hydrogen-bonded minima were identified: the global minimum where HX acts as the hydrogen bond donor and a local minimum where HX acts as the hydrogen bond acceptor. A halogenbonded local minimum was also identified for all but the fluorine mixed dimer. To the best of our knowledge, three of the minima are identified here for the first time. The hydrogen-and halogen-bonded local minima of each complex become more energetically competitive with the global minimum as the atomic radius of the halogen atom increases. CCSD(T) relative energies of the hydrogen-bonded local minima computed near the CBS limit decrease from 4.5 kcal mol −1 for HCN/HF to 2.9, 2.4, and 1.2 kcal mol −1 for X = Cl, Br, and I, respectively. Corresponding relative energies for the halogen-bonded local minima range from 4.0 kcal mol −1 for X = Cl to 2.7 kcal mol −1 for X = Br and to as little as 0.5 kcal mol −1 X = I. Harmonic vibrational frequency shifts reported here suggest that it may be feasible to differentiate between the various minima for X = Cl, Br, and I via spectroscopic analysis, as was the case for the HCN/HF dimer.

London Dispersion-Assisted Low-Temperature Gas Phase Synthesis of Hydrogen Bond-Inserted Complexes

“…5 Halogen bonding to the N end of HCN becomes increasingly competitive with hydrogen bonding on increasing the size of the halogen. 6 In aqueous solution, methyl halides have an increasing affinity toward porphyrins and other hosts. 7 In axial-equatorial equilibria of halogenated cyclohexanes, steric and London dispersion contributions compete with each other.…”

Characterization of non-covalent contacts in mono- and di-halo substituted acetaldehydes: probing the substitution effects of electron donating and withdrawing groups

“…The evaluation of the energies of non-covalent interactions is of importance in the literature. [24][25][26] Furthermore, a topological analysis of the electron density based on quantum theory of atoms in molecules (QTAIM) 27 and non-covalent interaction reduced density gradient (NCI-RDG) 28 isosurfaces has also been performed to indirectly evaluate the nature of these NCIs. The subtle changes in the geometrical and the associated electronic properties have been probed via the presence of different electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) or substituents in dimers of these molecules.…”

Hydrogen Bonding versus Halogen Bonding: Spectroscopic Investigation of Gas‐Phase Complexes Involving Bromide and Chloromethanes

“…[28,29] The binding strength of a halogen bond is also highly dependent on how readily electron density can be withdrawn from the halogen, an example of which being the halogen bonded HCI•••HCN dimer complex having a strength of 2.5 kJ mol À 1 , increasing to 11.3 kJ mol À 1 for the halogen bonded HI•••HCN complex. [30] Other types of interactions related to halogen bonding include chalcogen bonding, [31][32][33] and pnicogen bonding, [34][35][36] which in some cases have been shown to be similar in strength. [37,38] Halogen bonding interactions have been compared to hydrogen bonding previously, often with a focus on crystal structures or neutral gas-phase species.…”

“…[37,38] Halogen bonding interactions have been compared to hydrogen bonding previously, often with a focus on crystal structures or neutral gas-phase species. [30,[39][40][41][42] This study aims to expand these comparisons to hydrogen and halogen bonding with charged species, and how these interactions differ with respect to their neutral counterparts.…”

“…This highlights that directionality is an important factor when considering non‐covalent interactions [28,29] . The binding strength of a halogen bond is also highly dependent on how readily electron density can be withdrawn from the halogen, an example of which being the halogen bonded HCI⋅⋅⋅HCN dimer complex having a strength of 2.5 kJ mol −1 , increasing to 11.3 kJ mol −1 for the halogen bonded HI⋅⋅⋅HCN complex [30] . Other types of interactions related to halogen bonding include chalcogen bonding, [31–33] and pnicogen bonding, [34–36] which in some cases have been shown to be similar in strength [37,38] .…”