An insight into characteristics of nonconventional hydrogen bonds in the complexes of haloforms with carbon monoxide

The interaction between X3CH (X=F, Cl, Br) and CO were investigated through ab initio methods. The stability of complexes and their nonconventional C-H···O hydrogen bond decreases as the C-H polarity in haloform declines in the order Br3CH > Cl3CH > F3CH. The C-H blue shift of C-H···O hydrogen bonds increases from F3CH···OC to Br3CH···OC due to the decreasing occupation at antibonding σ*(C-H) orbitals when X goes from F to Br. The formation of C-H···O hydrogen bonds in X3CH···OC are found at the intermolecular C···O distance from 2.9 to 3.7 Å. The C-H blue shift decreases as the intermolecular distance between monomers increases. Remarkably, the significant contribution of dispersion component is observed along with the decreasing C-H blue shift at the equilibrium C···O distance region of 3.3-3.7 Å. The SAPT2+ analysis reveals a dominant contribution of dispersion and electrostatic components to complex stabilization, with the dispersion term playing a larger role.