Using one halogen bond to change the nature of a second bond in ternary complexes with P center dot center dot center dot Cl and F center dot center dot center dot Cl halogen bonds

作者：Del Bene Janet E^*; Alkorta Ibon^*; Elguero Jose

来源：Faraday Discussions, 2017, 203: 29-45.

DOI：10.1039/c7fd00048k

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the effect of the presence of one halogen bond on the nature of the other in ternary complexes H2XP:ClF:ClH and H2XP:ClF:ClF, for X = F, Cl, H, NC, and CN. The P center dot center dot center dot Cl bonds remain chlorine-shared halogen bonds in the ternary complexes H2XP:ClF:ClH, although the degree of chlorine sharing increases relative to the corresponding binary complexes. The F center dot center dot center dot Cl bonds in the ternary complexes remain traditional halogen bonds. The binding energies of the complexes H2XP:ClF:ClH increase relative to the corresponding binary complexes, and nonadditivities of binding energies are synergistic. In contrast, the presence of two halogen bonds in the ternary complexes H2XP:ClF:ClF has a dramatic effect on the nature of these bonds in the four most strongly bound complexes. In these, chlorine transfer occurs across the P center dot center dot center dot Cl halogen bond to produce complexes represented as (H2XP-Cl)(+): (-)(F:ClF). In the ion-pair, the cation is also halogen bonded to the anion by a Cl center dot center dot center dot F- halogen bond, while the anion is stabilized by an F-center dot center dot center dot Cl halogen bond. The central ClF molecule no longer exists as a molecule. The binding energies of the ternary H2XP:ClF:ClF complexes are significantly greater than the binding energies of the H2XP:ClF:ClH complexes, and nonadditivities exhibit large synergistic effects. The Wiberg bond indexes for the complexes H2XP:ClF, H2XP:ClF:ClH, and H2XP:ClF:ClF, and the cations (H2XP-Cl)(+) reflect the changes in the P-Cl and Cl-F bonds. Similarly, EOM-CCSD spin-spin coupling constants are also consistent with the changes in these same bonds. In particular, (1x)J(P-Cl) in H2XP: ClF complexes becomes (1J)(P-Cl) in the ternary complexes with chlorine-transferred halogen bonds. A plot of these coupling constants shows a change in the curvature of the trendline as chlorine-shared halogen bonds in H2XP: ClF: ClH become chlorine-transferred halogen bonds in H2XP:ClF:ClF. (1x)J(F-Cl) coupling constants also reflect changes in the nature of F center dot center dot center dot Cl halogen bonds.

• 出版日期2017-10-1