The Geometry and Nature of C─I···O─N Interactions in Perfluoroiodobenzene‐Pyridine N‐oxide Halogen‐Bonded Complexes

• Published in: Advanced science 2024-08, Vol.11 (30), p.e2403945-n/a
• Main Authors: Rautiainen, Juha Mikko, Valkonen, Arto, Lundell, Jan, Rissanen, Kari, Puttreddy, Rakesh
• Format: Article
• Language: English
• Subjects: Fluorine; halogen bond; Iodine; N‐oxide; perfluoroiodobenzene; sigma hole; Solvents; X‐ray structure
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.202403945

The N─Oxide oxygen in the 111 C─I···⁻O─N+ halogen bond (XB) complexes, formed by five perfluoroiodobenzene XB donors and 32 pyridine N‐oxides (PyNO) XB acceptors, exhibits three XB modes: bidentate, tridentate, and monodentate. Their C─I···O XB angles range from 148° to 180°, reflecting the iodine σ‐hole's structure‐guiding influence. The I···⁻O─N+ angles range from 87° to 152°. On the contrary, the I···⁻O─N+ angles have a narrower range from 107° to 125° in stronger monodentate N─I···⁻O─N+ XBs of N‐iodoimides and PyNOs. The C─I···⁻O─N+ systems exhibit a larger variation in I···⁻O─N+ angles due to weaker XB donor perfluoroiodoaromatics forming weak I···O XBs, which allows wider access to electron‐rich N‐O group regions. Density Functional Theory analysis shows that I···O interactions are attractive even when the I···⁻O─N+ angle is ≈80°. Correlation analysis of structural parameters showed that weak I···O XBs in perfluoroiodobenzene‐PyNO complexes affect the C─I bond via n(O)→σ*(C─I) donation less than the N─I bond via n(O)→σ*(N─I) donation in very strong I···O XBs of N‐iodoimide‐PyNO complexes. This implies that PyNOs' oxygen self‐tunes its XB acceptor property, dependent on the XB donor σ‐hole strength affecting the bonding denticity, geometry, and interaction energies. The analysis of 111 C–I···⁻O─N+ halogen‐bonded complexes formed by perfluoroiodobenzenes and pyridine N‐oxides has provided conclusive evidence that I···O halogen bonds are narrowly directional as per the halogen σ‐hole theory. The directionality observed from the N‐oxides viewpoint is significantly larger due to their N‐oxide oxygen atom's polydentate feature.