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

Three diaryliodonium tetrachloroaurates(III), [Ar 1 IAr 2 ][AuCl 4 ] (Ar 1 /Ar 2 = Ph/Ph ( 1 ), Ph/Mes ( 2 ), o -(C 6 H 4 ) 2 ( 3 )), were obtained as solids (62–80%) by the metathetical reaction of [Ar 1 IAr 2 ](CF 3 CO 2 ) and H[AuCl 4 ]. In particular, the single-crystal X-ray diffraction studies of 1 – 3 revealed three-center bifurcated C–I···( Cl –Au– Cl ) halogen bond (XB) and the more conventional interionic two-center C–I···Cl–Au XB. An XB with the iodine(III) center of a diaryliodonium cation can be formed even when ∠(C–I···X) is much less than 180° (decrease by 55° 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 ωB97XD/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.