RESUMO
The NâOxide oxygen in the 111 CâI···â»OâN+ 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 CâI···O XB angles range from 148° to 180°, reflecting the iodine σ-hole's structure-guiding influence. The I···â»OâN+ angles range from 87° to 152°. On the contrary, the I···â»OâN+ angles have a narrower range from 107° to 125° in stronger monodentate NâI···â»OâN+ XBs of N-iodoimides and PyNOs. The CâI···â»OâN+ systems exhibit a larger variation in I···â»OâN+ 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···â»OâN+ angle is ≈80°. Correlation analysis of structural parameters showed that weak I···O XBs in perfluoroiodobenzene-PyNO complexes affect the CâI bond via n(O)âσ*(CâI) donation less than the NâI bond via n(O)âσ*(NâI) 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.