Structures and properties of halogen bonds between cyanide and dihalogen molecules

Abstract

A systematic theoretical study of halogen-bonded complexes R-C≡N...BrY(R=F,Cl,Br,C≡CH,CH==CH2,CH3,C2H5;Y=F,Cl,Br) was performed at the MP2/aug-cc-pVDZ level of theory.The nature and characteristics of the halogen bonds were studied by ab initio calculations and the quantum theory of "atoms in molecules"(QTAIM).Electrostatic potentials,equilibrium geometries,vibrational frequencies,and topological properties of the electron densities were investigated systematically.The results show that n-type halogen bonds are formed between RCN and BrY and that the studied halogen-bonding interactions are all "closed-shell" electrostatic interactions.Complex formation results in elongation of the Br-Y bond and a red-shift of its vibrational frequencies.The inductive effects of substituents on the cyanide significantly influence the complex geometries,strengths of the halogen-bonding interactions,topological properties of the electron densities,and atom basin integral properties.The electrostatic potentials correlate well with the strengths of the halogen-bonding interactions and the electron-density topological parameters(ρ(rc),▽2ρ(rc),Gc,Hc,-Gc/Vc).Charge transfers were observed from RCN to BrY in the formation of the halogen-bonded complexes.The energy,dipolar polarization,and atomic volume of the bromine atom all decrease upon complex formation.