Hydrogen bonds and halogen bonds in complexes of carbones L→C←L as electron donors to HF and ClF, for L = CO, N2, HNC, PH3, and SH2

Abstract

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to determine the structures and binding energies of the carbone complexes in which the carbone L→C←L acts as an electron pair donor to one and two HF or ClF molecules, for L = CO, N₂, HNC, PH₃, and SH₂. The binding energies increase with respect to the ligand in the order CO < NN < CNH ≪ PH₃ < SH₂, and increase with respect to the acid in the order HF < 2 HF < ClF < 2 ClF. The complexes with the ligands CO, N₂ and PH₃ have C_2v symmetry while those with CNH and SH₂ have C_s symmetry, except for H₂S→C←SH₂:2HF which has C₂ symmetry and a unique structure among all of the carbone complexes. F–H and Cl–F stretching frequencies in the complexes decrease as the F–H and Cl–F distances, respectively, increase. EOM-CCSD spin–spin coupling constants ^2hJ(F–C) increase with decreasing F–C distance. Although the F–H⋯C hydrogen bonds gain some proton-shared character in the most tightly bound complexes, the hydrogen bonds remain traditional hydrogen bonds. ^1xJ(Cl–C) values indicate that the Cl⋯C halogen bonds have chlorine shared character even at the longest distances. ^1xJ(Cl–C) then increases as the Cl–C distance decreases, and reaches a maximum for chlorine-shared halogen bonds. As the Cl–C distance further decreases, the halogen bond becomes a chlorine-transferred halogen bond.