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

Three
diaryliodonium tetrachloroaurates­(III), [Ar1IAr2]­[AuCl4] (Ar1/Ar2 = Ph/Ph
(1), Ph/Mes (2), o-(C6H4)2 (3)), were obtained
as solids (62–80%) by the metathetical reaction of [Ar1IAr2]­(CF3CO2) and H­[AuCl4]. 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.