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.
RESUMO
Seven pyridine iodine(I) sulfonate complexes were prepared and isolated at low temperatures and characterized by X-ray diffraction analysis. The inherently instable pyridine iodine(I) cations are stabilized by an oxygen of sulfonate anions via the Iâ â â O halogen bond. In these complexes, the iodine atom of the pyridine iodine(I) cation acts as an electron acceptor and the sulfonate oxygen as the electron donor. These complexes are stable enough in the crystalline state, yet decompose rapidly under ambient conditions, also being unstable in solution. The (pyridine)N-I bond lengths [2.140(3)-2.197(2)â Å] and the Iâ â â O halogen bonds [2.345(6)-2.227(3)â Å] are analogous to (imide)N-Iâ â â O-N-pyridine uncharged halogen-bonded complexes formed from N-haloimides and pyridine N-oxides, thus confirming the existence of elusive pyridine iodine(I) cation.