Quantum Chemical Dissection of the Shortest P=O⋅⋅⋅I Halogen Bond: The Decisive Role of Crystal Packing Effects

Abstract

A supramolecular arrangement comprising a bridged triarylphoshine oxide and an aryl iodide is reported, featuring the shortest ever reported P=O⋅⋅⋅I halogen bond of 2.683(5) Å in the solid state. X-ray crystallographic analysis together with modern quantum chemical methods were enlisted to dissect the individual contributions that compelled this exceptionally short halogen bond, pointing out the decisive role of crystal packing effects.

Bridged triarylboranes, ‐silanes, ‐amines, and ‐phosphines as minimalistic heteroatom‐containing polycyclic aromatic hydrocarbons: Progress and challenges

“…The careful molecular design of this scaffold provided for the formation of a stable phosphine oxide radical anion, which could be studied by X‐ray crystallography for the first time. In addition, cocrystallization of the neutral phosphine oxide with an electron‐deficient aryl diiodide afforded a halogen‐bonded 2:1 complex featuring the shortest hitherto reported P═O···I distance in the solid state ( vide infra ) …”

“…The final dehydrative cyclization was achieved in polyphosphoric acid at 200 °C producing phosphine oxide 77 as a colorless microcrystalline powder. The unique structural situation in 77 results in an increased electron density at the phosphoryl oxygen as a result of the congested bowl‐shaped structure, which prompted us to test this compound as a halogen bond acceptor with 1,4‐diiodotetrafluorobenzene . Indeed, X‐ray crystallographic analysis suggested exceptionally strong halogen bonding interactions between the two constituents in the solid state (Figure B).…”

“…A, Preparation of trispirocyclic phosphine oxide 77 and B, halogen‐bonded 2:1 complex formed with 1,4‐diiodotetrafluorobenzene in the solid state; C, chemical one‐electron reduction to radical anion 77 •– , crystal structure of 77 •– [K⊂18‐crown‐6] + , and Mulliken spin densities from DFT calculations (blue: “–”, red: “+” spin density) together with the coupling constants from EPR measurements; adapted from Kivala and coworkers and with permission of Wiley‐VCH…”

Comparison of Various Means of Evaluating Molecular Electrostatic Potentials for Noncovalent Interactions

“…It is not only HBs that have been examined in the context of electrostatic attraction as a possible driving force but also a number of closely related interactions. The replacement of the bridging H atom by a halogen leads to the now well‐known halogen bond, which has striking similarities with the HB, despite the much larger shared atom. Halogen and HBs have comparable strength, strive toward linearity, can be decomposed into components of similar magnitude, and manifest the same sort of n→σ* charge transfer phenomenon.…”

Possible Case of Halogen Bond‐Driven Self‐Disproportionation of Enantiomers (SDE) via Achiral Chromatography

“…The results of the crystallographic study were quite remarkable, suggesting a possibility of a halogen bond between C=O groups and the ortho ‐bromine atoms in the racemic crystals. The presence of the halogen bond in the racemic crystal makes them more stable than the chiral crystal.…”