The C-I···-O-N+Halogen Bonds with Tetraiodoethylene and Aromatic N-Oxides
Research output: Contribution to journal › Article › Scientific › peer-review
|Number of pages||8|
|Journal||Crystal Growth and Design|
|Publication status||Published - 5 Aug 2020|
|Publication type||A1 Journal article-refereed|
The nature of C-I···-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···O halogen bond distances are similar to well-known perfluorohaloalkane/-arene donor-PyNO analogues. With C2I4, oxygens of the N-oxides adopt exclusively μ2-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···(μ-PyNO)2···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···O bond parameters demonstrates that the ?-bond between four iodine atoms also plays an important role in enhancing the σ-hole strength. DFT-Based monodentate XB interaction energies, ?Eint, 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···-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 mol-1] and C6F5I·(pyridine N-oxide) [32.3 kJ mol-1].