The C-I•••-O-N+ Halogen Bonds with Tetraiodoethylene and Aromatic N-Oxides

The nature of C-I center dot center dot center dot O--N+ interactions, the first of its kind, between nonfluorinated tetraiodoethylene halogen bond (XB) donor and pyridine N-oxides (PyNO) are studied by single-crystal X-ray diffraction and density functional theory (DFT) calculations. Despite the nonfluorinated nature of the C2I4, the I center dot center dot O halogen bond distances are similar to well-known perfluorohaloalkane/-arene donor-PyNO analogues. With C2I4, oxygens of the N-oxides adopt exclusively mu(2)-XB coordination in contrast to the versatile bonding modes observed with perfluorinated XB donors. The C2I4 as the XB donor forms with PyNO's one-dimensional chain polymer structures in which the C2I4 center dot center dot center dot(mu-PyNO)(2)center dot center dot center dot C2I4 segments manifest two bonding motifs, namely, side-by-side (vicinal di-iodo) and head-to-head (geminal di-iodo), due to the nearly symmetric square-planar structure of the C2I4. While the attractive nature between I and O atoms is mainly electrostatic, the narrow range of C center dot center dot center dot O bond parameters demonstrates that the jr-bond between four iodine atoms also plays an important role in enhancing the sigma-hole strength. DFT-Based monodentate XB interaction energies, Delta E-int, in 13 1:1 XB complexes vary between 31.9 and 46.5 kJ mol(-)(1), the strongest remarkably exceeding the value reported for I-I center dot center dot center dot O--N+ = 42.0 kJ mol(-)(1). In the case of C2I4.(pyridine N-oxide) [31.9 kJ mol(-1)], the monodentate XB energy is on a par with perfluorinated donor complexes, namely, CF3I. (pyridine N-oxide) [31.1 kJ moI(-1)] and C6F3I. (pyridine N-oxide) [32.3 kJ mol(-1)].