Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

Abstract

The characteristics and structures of single-electron halogen bond complexes [H 3 C⋅⋅⋅Br-Y (Y = H, CCH, CN, NC, C 2 H 3 )] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H 3 C⋅⋅⋅Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH 3 (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a "three-electron bond". Due to the formation of the single-electron Br bond, the C-H bonds of the CH 3 radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.single-electron halogen bond, single-electron hydrogen bond, single-electron lithium bond, MP2, DFT, NBO, AIM

Theoretical characterization of single-electron iodine-bond weak interactions in CH3…I-Y(Y = BH2, H, CH3, C2H3, C2H, CN, NC) systems

“…Here, the C···I distances in the complexes of CH 3 ···I-H, CH 3 ···I-CH 3 , CH 3 ···I-CHCH 2 , CH 3 ···I-CCH, CH 3 ···I-CN and CH 3 ···I -NC obtained at the B3LYP/6-311++G** level are 0.3699, 0.3671, 0.3686, 0.3435, 0.3252 and 0.2917 nm, respectively, which are all less than the sum of the van der Waals radii of the carbon atom (0.170 nm) and the iodine atom (0.198 nm) [21]; this is part of the evidence for the existence of single-electron iodine-bond interactions. The C···I bond distances in the present study are shorter than the C···Br bond lengths reported for single-electron Br-bond systems in our previous study [11]. Furthermore, the bond angles among the three atoms involved in SEXBs are all close to 180°, and the two moieties exhibit "T" shapes in space.…”

“…The singleelectron halogen-bond (SEXB) interaction is one of these single-electron noncovalent interactions. However, only the single-electron bromine-bond has been studied [10][11][12], and neither experimental nor theoretical studies of the other SEXBs involving iodine have been reported. It is known that the iodine atom has more polarity and distortion than bromine atom.…”

How Do Distance and Solvent Affect Halogen Bonding Involving Negatively Charged Donors?

“…The NBO calculation has been deemed as a useful tool to analyze the noncovalent interactions. ,,− The second-order perturbation stabilization energy, E (2), is an important indicator to evaluate the strength of a noncovalent interaction, which was calculated using the same method as that used in ref . To get further insight into negative halogen bonding, NBO-based analysis was performed on the monomers and complexes at the M06-2 X /6-311++G­(d,p)/SDD level using the NBO program implemented in the Gaussian 09 package.…”

Single Electron Pnicogen Bonded Complexes

“…In view of the similarities between halogen bonding and lithium bonding with H-bonding, the existence of a single electron halogen bond − and a single electron lithium bond has been reported theoretically.…”