Electron Delocalization in Benzo(thia)oxazolothiazinium Heterocycles and Ability to the -Hole Tetrel Bond Formation

The characteristics of electron delocalization and the specific ability to form noncovalent interactions with triiodide anions are studied for the series of synthesized benzo(thia)oxazolothiazinium crystals. The S/O "switching" in the oxazolo/thiazolo fragment in heterocyclic cations does not lead to isostructural crystal packing. The points of interest in these structures are the types of noncovalent bonds and the "perpendicular" bond paths formed by the different sorts of carbon atoms in five- and six-membered cycles with the iodine atoms of oligoiodide anions located under and above the conjugated heterocyclic system. Periodic density functional theory (DFT) calculations have been used to estimate the broad spectrum of quantum chemical descriptors: electrostatic, exchange-correlation, fermionic one-electron potentials, and electron density topological characteristics. We demonstrate that the electron-deficient carbon atom bound with N, O(S), and S heteroatoms at the junction of (thia)oxazolo- and thiazinium cycles truly participates in the C center dot center dot center dot I pi-hole tetrel bond. The other bridged C atoms of the annulated benzene ring are also electron deficient in heterocyclic cations; however, they are characterized by too changeable electron delocalization in six-membered cycles in a crystalline environment.