Bifurcated Halogen Bonding Involving Diaryliodonium Cations as Iodine(III)-Based Double-σ-Hole Donors

Three diaryliodonium tetrachloroaurates(III), [(ArIAr2)-I-1][AuCl4] (Ar-1/Ar-2 = Ph/Ph (1), Ph/Mes (2), o-(C6H4)(2) (3)), were obtained as solids (62-80%) by the metathetical reaction of [(ArIAr2)-I-1](CF3CO2) and H[AuCl4]. In particular, the single-crystal X-ray diffraction studies of 1-3 revealed three-center bifurcated C-I center dot center dot center dot(Cl-Au-Cl) halogen bond (XB) and the more conventional interionic two-center C-I center dot center dot center dot Cl-Au XB. An XB with the iodine(III) center of a diaryliodonium cation can be formed even when angle(C-I center dot center dot center dot X) is much less than 180 degrees (decrease by 55 degrees in our experiments). A Cambridge Structural Database search and processing revealed other examples of bifurcated XBs involving diaryliodonium species. All recognized bifurcated XBs with diaryliodonium cations were classified and divided into two categories: bifurcated plus two-center and double-bifurcated structural types. The nature and energies of the XB interactions were studied by density functional theory (DFT) calculations and a topological analysis of the electron density distribution in the framework of the quantum theory of atoms in molecules (QTAIM) at the omega B97XD/DZP-DKH level of theory. The nature of all XB contacts is purely noncovalent, and the total energy of bifurcated XBs is generally ca. 50% higher than the energy of two-center XBs.

Automated summary

Three diaryliodonium tetrachloroaurates(III) were synthesized and their crystal structures revealed both three-center bifurcated halogen bonds and conventional two-center halogen bonds. Density functional theory calculations showed that the nature of these interactions is purely noncovalent, with the energies of bifurcated halogen bonds generally higher than those of two-center halogen bonds.